4V+'*>,1(=% - Institut Néelneel.cnrs.fr/IMG/pdf/Brochure_2017-2018_WEB.pdf · 11 INSTITUT NEEL Grenoble Proposition de stage Master 1 - Année universitaire 2017-2018 Dilatation

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

Institut NEEL-CNRS 25, rue des Martyrs – Bâtiment - BP 166 – 38042 Grenoble cedex 9 – France

! +33 (0)4 76 88 74 68 ! +33 (0)4 76 88 12 30

L’Institut Néel est une unité propre du CNRS conventionnée avec l’Université Grenoble Alpes

2

3

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`)1,%AW24*'W(%,'%(+/,)(%A,%F-(),1%K=% a,%>0+(%(0+3-*),% 4-%5*,'>,'+,%[% 4V&'()*)+)%!W,48%-+%.0*'(% >*1)+,44,.,')% 7-1% 2,)),% 51023+1,% ,)% -+% )1->,1(% A,% '0)1,% (*),% 9,5% 999=',,4=2'1(=B1% Q% !V3W(*),Z% 7-(% [%20')-2),1%4,(%23,123,+1(%A,%4V&'()*)+)%!W,4%-B*'%A,%'0+(%1,'A1,%>*(*),=%

#)*,'',%HRSETUU#E%% % % % % % % % O*1,2),+1%&'()*)+)%!"#$%

S,7),.51, J<KL

Institut NEEL-CNRS 25, rue des Martyrs – Bâtiment - BP 166 – 38042 Grenoble cedex 9 – France

! +33 (0)4 76 88 74 68 ! +33 (0)4 76 88 12 30

L’Institut Néel est une unité propre du CNRS conventionnée avec l’Université Grenoble Alpes

4

5

6

7

INSTITUT NEEL Grenoble Proposition de stage Master 1 - Année universitaire 2017-2018

Table des matières Magnetic Separation: a new route for material recycling .......................................................... 9 Hydrures intermétalliques pour la conversion électrochimique ............................................... 10 Dilatation thermique des systèmes magnétiques à cages ......................................................... 11 Micro-anémomètrie thermique : caractérisation d’un prototype ultra-miniaturisé .................. 12 Turbulence Quantique : détecter les vortex superfluides ......................................................... 13 Cartographie thermique d’un écoulement ................................................................................ 14 Anémométrie à fibre optique .................................................................................................... 15 Mode de Higgs Supraconducteur ............................................................................................. 16

8

9

INSTITUT NEEL Grenoble

Proposition de stage Master 1 - Année universitaire 2017-2018

Magnetic Separation: a new route for material recycling

General Scope: The issue of so-called “critical” materials is crucial for the development of new technologies for energy (photovoltaic panels, magnets, batteries, etc...). In particular, rare earth (RE) elements are in the front line in Europe, because they combine both a very high supply risk together with a growing economic importance. In order to reduce the import pressure, it is necessary to develop a sustainable recycling process for Europe. To date, less than 1% of the rare earths are being recycled due to, amongst others, a lack of efficient and environmentally-friendly recycling technologies. In this subject, magnetic separation is presented as an alternative way to recycle RE-based scrap. As a physical separation method, magnetic sorting combines the advantage of being a robust, cost effective and environmentally-friendly technique. For magnetic separation purposes, HGMS devices (High Gradient Magnetic Separator) creating strong magnetic forces are developed at CNRS/Institut Néel. Your mission will be to conduct the experiments needed to demonstrate the recycling feasibility of various RE-based alloys. You will prepare powdered materials in view of the recycling process using various techniques based both on physics and chemistry, such as: dissolution, decomposition, milling, centrifugation, etc… You will perform tests of magnetic separation and finally characterize the final products (both from the magnetic and microstructural viewpoints) and exploit the results.

Research topic and facilities available You will benefit from the expertise of the TEMA group (Processing Elaboration Materials Applications, 6 persons) on the development of processes using intense magnetic fields, on the recycling processes as well as on the synthesis of alloys in various forms. Facilities available in the group include high superconducting magnets, various processing tools (induction cold crucible, furnaces, milling facilities, separation tools, etc…) and characterization devices (laser granulometry, ATD/TGA, microscopy, etc…). All common facilities from Institut Néel available as well (SEM, magnetic measurements, DRX, etc…) Possible collaboration and networking: This subject is part of the "Recup 'TR" project which deals with the recycling of Rare Earth elements contained in magnets and other Rare Earth based alloys. You will be involved with both academic and industrial contacts. Required skills: -Interest in the recycling and the valorization of by-products. -General curriculum with a specialty in Materials Science. -Autonomy, initiative and ability to work in a team and to adapt to a collaborative project, which includes partners from academic research and industry. -Knowledge in physicochemical processes and/or metallurgy is welcome. Starting date: Spring 2018 Contact: Sophie RIVOIRARD, Institut Néel - CNRS Phone:04 76 88 90 32 e-mail:[email protected] More information: http://neel.cnrs.fr, https://www.youtube.com/watch?v=QfLmRl44lG8.

10


Hydrures intermétalliques pour la conversion électrochimique

Cadre général : Matériaux pour le stockage et la conversion de l’énergie Ce nouvel axe de recherche transpose les matériaux de stockage de l’hydrogène vers les systèmes Li-ion. Des travaux menés il y a une dizaine d’années ont montré la possibilité d’utiliser des hydrures comme matériaux d’électrode négative pour batteries à ions lithium. La réaction idéale de conversion MHx + xLi+ + xe- ⇌ M + xLiH est possible pourvu que ΔGf(MHx)/x est plus grande que ΔGf(LiH). Les hydrures proposés à l’investigation ont déjà fait l’objet de nombreux travaux au sein de l’équipe (MgH2 allié aux métaux de transition ainsi que les solutions solides bcc. ). Un intérêt particulier sera porté aux pérovskites pseudo quaternaires du système NaMgH3.

Sujet exact, moyens disponibles : Le sujet proposé concerne la synthèse et la caractérisation structurale tandis que la caractérisation électrochimique est faite en collaboration au LRCS. L’objectif final est l’assemblage de ces matériaux avec des électrolytes solides en vue d’un objet modèle et prototype (type bouton). Interactions et collaborations éventuelles : LRCS Amiens (caractérisation électrochimique) groupe Ishikawa Hiroshima (électrolytes solides, assemblage) Formation / Compétences : Sciences des matériaux Diffraction des RX, DSC Période envisagée pour le début du stage : printemps 2018 Contact : Miraglia Salvatore Institut Néel - CNRS tél 04 76 88 79 42 mel [email protected] Plus d'informations sur : http://neel.cnrs.fr

11


Dilatation thermique des systèmes magnétiques à cages Cadre général : Les atome de terre-rare se caractérisent par une couche 4f incomplète, ce qui donne la possibilité d'y faire apparaître un moment magnétique et, également, des moments multipolaires électriques. Ces derniers traduisent l'asphéricité de la répartition des électrons 4f. Cette faculté de redistribution de la couche 4f intervient dans nombre de phénomènes importants dans les systèmes de terre-rares : champ cristallin, anisotropie magnétique, phénomènes magnétoélastiques. . . Si la terre-rare est dans un environnement très symétrique, la distribution 4f le sera également. Cependant, à basse température, la moindre déformation de son environnement aura un effet drastique sur la répartition des électrons 4f, abaissant l'énergie électrostatique de l'ensemble : on dit d'un tel système qu'il présente une instabilité Jahn-Teller. Sujet exact, moyens disponibles Certains composés de terre-rare adoptent des structures cristallographiques dans lesquelles l'atome magnétique dispose d'une latitude de déplacement élevée à l'intérieur d'une cage. Dans un tel environnement, le moyen d'expression le plus aisé de l'instabilité Jahn-Teller est un écart au centre de la cage (figure ci-dessus). Cela se manifesterait par une variation thermique caractéristique de la distribution de l'atome de terre-rare dans la cage. Parmi les conséquences de ce changement on attend, entre autres, un effet sur le volume du cristal à basse température. Pour mettre à l'épreuve ces prédictions, on se propose de mesurer la dilatation thermique de composés de terre-rare à cages, parmi les familles des hexaborures et skuterrudites remplies. Des mesures de chaleur spécifique y seront associées, puisque complémentaires : la levée de dégénérescence liée au décentrage a une répercussion directe sur l'entropie magnétique. Des approches par spectroscopie infrarouge sont également envisagées. L'analyse en mécanique quantique repose sur la modélisation du puits de potentiel de la cage, dont la forme évolue avec la température. Pour décrire les propriétés de dilatation ou magnétoélastiques, il faut le considérer comme élastiquement couplé à son environnement. Interactions et collaborations éventuelles : Au sein du département MCBT et plus particulièrement, l'équipe MAGSUP. Formation / Compétences :Connaissances de base en physique du solide et magnétisme. Aptitude au travail expérimental. Compétences en programmation, y compris labview, bienvenues. Période envisagée pour le début du stage : printemps 2018 Contact : Mehdi AMARA Institut Néel - CNRS tél 0476887913 mel [email protected] Plus d'informations sur : http://neel.cnrs.fr

Schéma illustrant l'abaissement de symétrie Jahn-

Teller par excentrage d'un ion terre-rare à l'intérieur d'une cage. Les niveaux d'énergie E4f du

fondamental sont séparés, tandis que le nuage électronique est redistribué.

12


Micro-anémomètrie thermique : caractérisation d’un prototype ultra-miniaturisé

Cadre général : La physique de la turbulence est étudiée depuis plus d’un siècle mais elle demeure un sujet ouvert. Au sein d’un écoulement turbulent, des tourbillons de tailles différentes interagissent. L’étude de ces interactions entre structures et la compréhension des caractéristiques des très petites échelles constitue un défi majeur qui nécessite la miniaturisation des sondes de mesure. Les capteurs doivent être suffisamment petits pour résoudre les plus petites structures tout en étant robustes et sensibles. Dans cet esprit, nous avons développé un nouveau principe d’anémomètre thermique nous permettant d’atteindre une résolution spatiale record de 5 microns. Il est maintenant important de caractériser sa réponse temporelle, spatiale, directionnelle,… et d’optimiser son fonctionnement.

Sujet, moyens disponibles :

Nous souhaitons accueillir un étudiant pour caractériser cette sonde. Pour cela, une soufflerie régulée en température sera utilisée pour produire un écoulement bien connu, la sonde étant montée sur une tête goniométrique. L’étudiant devra monter le banc de test, l’instrumenter et étudier la réponse dynamique de la sonde dans différentes configurations d’écoulement. Le traitement des données devra permettre de caractériser les performances de la sonde. Interactions et collaborations éventuelles : L’étudiant sera amené a interagir avec les équipes techniques du laboratoire, en particulier pour les questions de mécanique et électronique.

Formation / Compétences : Compétences développées: Instrumentation, Mesure, Métrologie, Hydrodynamique & Turbulence, Acquisition & Traitement du signal. Période envisagée pour le début du stage : indifférente. Durée de 2 mois. Contact : Roche Philippe, Institut Néel – CNRS/ Université Grenoble-Alpes [email protected] (04 76 88 11 52) http://hydro.cnrs.me

Anémomètre micro-fabriqué d’une résolution record de 5 microns

13


Turbulence Quantique : détecter les vortex superfluides Cadre général : En dessous de 2,17 K, l’hélium liquide acquiert des propriétés superfluides : il peut s’écouler sans viscosité et la vorticité de son champ de vitesse devient quantifiée. On s’attend donc à ce que sa turbulence, appelée « Turbulence Quantique », diffère de la turbulence « classique ».

D’après plusieurs études récentes, il semble que la principale différence soit concentrée au niveau des plus petits tourbillons présents dans ces deux types de turbulence. En effet, en l’absence d’une dissipation efficace, on s’attend à ce que les tourbillons superfluides s’accumulent aux petites échelles de l’écoulement.

L’objectif est de détecter et comprendre cette différence, grâce à un détecteur conçu à cet effet.


Dans le cadre du stage, l’étudiant caractérisera un capteur micro-fabriqué de densité de vortex quantiques. Ce capteur prend la forme d’une micro-cavité ouverte, traversée par l’écoulement. Dans cette cavité, une onde thermique (« onde de second son ») résonne et son facteur de qualité reflète en temps réel de la densité de vortex (cf plot). La dernière génération de capteurs présentant une forme originale à faible invasivité, elle sera caractérisée dans des écoulements d’hélium superfluide : cryostat de test en verre (photo), soufflerie TOUPIE… Interactions et collaborations éventuelles : Le projet s’inscrit dans le cadre de l’ANR EcouTurb, un projet d’étude des couches limites en turbulence quantique associant 5 laboratoires français relevant du CNRS, CEA, Université Grenoble Alpes, ENS-Lyon.

Formation / Compétences développés : Hydrodynamique & Turbulence quantique, Physique des basses températures & Cryogénie, Acquisition & Traitement du signal, Instrumentation & Mesures bas bruit Période envisagée pour le début du stage : indifférente – Durée de 2 mois Contact : Roche Philippe, Institut Néel – CNRS/Université Grenoble-Alpes [email protected] (04 76 88 11 52) http://hydro.cnrs.me

T

Cryostat pour tests dans du superfluide

1

Résonances de second son en présence d’écoulement (pointillés) et en l’absence

(ligne continue) d’écoulement

2

14


Cartographie thermique d’un écoulement Cadre général : Depuis sa première observation, il y a une quinzaine d’années par notre équipe, le « Régime Ultime de la convection » est devenu l’objet d’une riche polémique scientifique.

Ce régime transporte la chaleur bien plus efficacement que tout autre, et semble confirmer un modèle théorique vieux d’un demi siècle et prédisant l’existence d’un régime entièrement turbulent.

Toutefois, les conditions qui permettent le déclenchement de ce régime échappent toujours à la compréhension, malgré la mise en œuvre de moyens expérimentaux et numériques très importants dans une dizaine de pays.

Sujet, moyens disponibles : Dans le cadre du stage, l’étudiant travaillera sur un nouveau type de capteur permettant de mesurer simultanément la température en 8 points de l’espace formant un cube. Cela permet de d’estimer les 3 composantes du gradient de température de l’écoulement, et de remonter ainsi à une quantité déterminante dans le bilan thermique. C’est la première fois qu’un tel capteur est micro-fabriqué.

Le but sera de caractériser ce capteur (ses forces, ses limites), en le plaçant dans des écoulements d’air bien contrôlés. A l’issue du stage, des modifications de design du capteur seront proposées. Interactions et collaborations éventuelles : Le projet s’inscrit dans le cadre d’une collaboration avec l’Université d’Ilmenau, en Allemagne. Cette université dispose de la plus grande cellule de convection au monde.

Formation / Compétences : Compétences développées: Instrumentation & Mesures bas bruit, Hydrodynamique, Acquisition &

Traitement du signal. Période envisagée pour le début du stage : indifférente – durée de 2 mois Contact : Roche Philippe, Institut Néel – CNRS/ Université Grenoble-Alpes [email protected] (04 76 88 11 52) http://hydro.cnrs.me

C

Capteur micro-fabriqué permettant une mesure de température en 8 points de l’espace, chacun

disposé à un sommet d’un cube

15


Anémométrie à fibre optique Cadre général : La physique de la turbulence est étudiée depuis plus d’un siècle mais elle demeure un sujet ouvert. Au sein d’un écoulement turbulent, des tourbillons de tailles différentes interagissent. L’étude de ces interactions entre structures et la compréhension des caractéristiques des très petites échelles constitue un défi majeur qui nécessite la miniaturisation des sondes de mesure. Les capteurs doivent être suffisamment petits pour résoudre les plus petites structures tout en étant robustes et sensibles. Dans cet esprit, nous avons entrepris à l’Institut Néel le développement d’un anémomètre à fibre optique. Les premiers essais ont montré que le principe de fonctionnement de la sonde est valide (voir Figure). Un nouveau prototype est en cours de réalisation. Afin de permettre l’exploitation de la sonde, il est maintenant important de caractériser sa réponse dans un écoulement.

Fig. [à gauche] L’écoulement arrive par la gauche et défléchit la membrane. Son déplacement est mesuré par la fibre optique (d’après Watson et al.) [à droite] Capteur commercial à fibre (FISO).


Nous souhaitons accueillir un étudiant pour caractériser cette sonde. Pour cela, un écoulement d’air comprimé filtré et/ou d’eau sera utilisé pour produire un écoulement connu, la sonde étant montée sur une tête goniométrique. L’étudiant devra monter le banc de test et l’instrumenter. Il étudiera ensuite la réponse dynamique de la sonde en fonction de l’angle d’incidence. Le traitement des données devra permettre de caractériser les performances de la sonde. De ce travail dépendra la nouvelle génération de ce type de capteur. Interactions et collaborations éventuelles :L’anémomètre est développé au sein d’une collaboration interne à l’Institut Néel, entre des hydrodynamiciens et des opticiens. L’étudiant sera amené a interagir pleinement avec les différents acteurs de la collaboration. Il devra également collaborer avec les équipes techniques du laboratoire pour les questions de mécanique.

Formation / Compétences : Compétences développées: Optique fibrée, Instrumentation, Hydrodynamique & Turbulence, Acquisition & Traitement du signal. Période envisagée pour le début du stage : indifférente – durée 2 mois Contact : Roche Philippe, Institut Néel – CNRS/ Université Grenoble-Alpes [email protected] (04 76 88 11 52) http://hydro.cnrs.me (contacts alternatifs : Jochen Fick, [email protected] )

T

16


Mode de Higgs Supraconducteur Cadre général : Les supraconducteurs sont des matériaux aux propriétés étonnantes. Ils sont connus pour permettre de faire léviter un aimant, ou de léviter sur un aimant voire les deux (Cf. figure). Ils sont aussi le siège de propriétés quantiques à la pointe de la recherche actuelle. Notamment, une fois l’état de base de l’état supraconducteur atteint, les électrons supraconducteurs expérimentent deux types de fluctuations :

les fluctuations de la phase de l’état quantique globale de tous les électrons supraconducteurs (aussi appelé condensat) ou les fluctuations de l’amplitude de cet état (Cf. Fig). Ce dernier mode de fluctuations est analogue au boson de Higgs de la physique des particules. Comme celui-ci, bien qu’aussi un mode ‘textbook’, il est extrêmement difficile à observer car il ne se couple à aucune sonde. Ce stage a pour objet la recherche et l’étude d’un tel mode dans une série de composés supraconducteurs. Sujet exact, moyens disponibles : Dans la littérature, un seul cas d’observation de ce mode est reporté, il s’agit du composé NbSe2 dans lequel l’état supraconducteur coexiste avec un autre ordre électronique, nommé onde de densité de charge. Cette observation a été faite par spectroscopie Raman à travers l’observation d’un mode associé à l’onde de densité de charge. L’étudiant.e. aura pour objectif d’étudier une autre famille de composé dans laquelle la supraconductivité coexiste avec un autre type d’ordre électronique, mais qui pourrait aussi donner lieu à l’observation du mode de Higgs. Nous recherchons ainsi à définir une universalité de l’observabilité du mode de Higgs supraconducteur. Pour cela, il/elle réalisera des expériences de spectroscopie Raman en conditions extrèmes de température et/ou de haute pression. Interactions et collaborations éventuelles : Nous avons déjà une collaboration établie avec une théoricienne (Lara Benfatto, La Sapienza, Rome) sur ce sujet. Nous sommes en lien étroit avec nos collaborateurs synthétisant les cristaux. Et de façon générale, ce stage s’insère dans un projet ANR

Formation / Compétences : Physique de la Matière condensée, curiosité et goût pour les expériences délicates.

Période envisagée pour le début du stage : mars-mai 2018 Contact : Méasson Marie-aude Institut Néel - CNRS : [email protected] Plus d'informations sur : http://neel.cnrs.fr

SC

SC aimant

Energy libre de l’état supraconducteur en fonction de la partie réelle et imaginaire du paramètre d’ordre. Autour de la position d’équilibre, deux types de fluctuations existent. Les fluctuations de l’amplitude, ou mode de Higgs, est au cœur de cette proposition de stage.

17

18

19


Table des matières Magnetic Separation: a new route for material recycling ........................................................ 23 Coherent control of the spin of an individual magnetic atom with surface acoustic waves .... 24 Hybrid nanowires for topological quantum computing ........................................................... 25 Single photon sources based on quantum dot semiconductor nanowires ................................ 26 Artificial frustrated spin systems .............................................................................................. 27 Superconductivity in atomic-scale magnetic nanostructures ................................................... 28 Quantum electronic transport probed by thermoelectricity ...................................................... 29 Monochromatic on-demand single-electron source ................................................................. 30 Spin-orbitronics mediated by one-atom-thin graphene ............................................................ 31 Triplet photon generation in optical non linear waveguides .................................................... 32 Garnet nanocrystals for white LEDs ........................................................................................ 33 Recherche de la supraconductivité dans des bi-couches de graphène sous haute pression ..... 34 Étude de la compétition sous haute pression entre les ordres de charge et la supraconductivité dans les cuprates de mercure à haute température critique ...................................................... 35 Recherche de nouveaux supraconducteurs à haute température critique ................................. 36 Synthèse et caractérisation structurale de nouvelles ferrites de Ba/Bi ..................................... 37 Circuit-QED: amplification at the single-photon level ............................................................ 38 Quantum modeling of nano-structured solar cells ................................................................... 39 Coupling a single quantum dot to a mechanical oscillator ....................................................... 40 Quantum randomness: Energetic and entropic features ........................................................... 41 Bio-Activation of Mesoporous Silica Nanoparticles by selective DNA destructuration ......... 42 Magnetic fragmentation in the Nd-based pyrochlore compounds ........................................... 42 Chemical mapping at the sub-nm scale of ultraviolet µ-LEDs Cartographie chimique à l’échelle sub-nanométrique de dispositifs µ-LEDS pour UV ................................................. 44 Charge transport in organic semiconductors: atomistic investigation of dynamic disorder .... 45 Nonlinear optics with hybrid plasmonic nanostructures .......................................................... 46 Photon pair generation in hybrid nonlinear/plasmonic nanostructures .................................... 47 Graphene based superconducting quantum bit ......................................................................... 48 Theory of topological properties in microwave-irradiated Josephson junctions ..................... 49 Quantum Hall interferometry in high mobility Graphene ........................................................ 50 Dielectric properties of the Cooper-pair insulator .................................................................... 51 Dynamics of many-body systems in quantum electronics ....................................................... 52

20

Novel quantum interference experiments with ultra-short single electron charge pulses ........ 53 Quantum superpositions of causal relations ............................................................................. 54 Circuit-QED: amplification at the single-photon level ............................................................ 55 Confined nucleation and growth of molecular nanocrystals for biophotonics and advanced solid-state NMR ....................................................................................................................... 56 New generation of eco-efficient phosphors for white LED lighting. ....................................... 57 Spin Polarisation in Graphene Functionalized with 2D MolecularAssemblies ....................... 58 Non-linear phenomena in topological phases of matter ........................................................... 59 Interacting topological matter out of equilibrium .................................................................... 60 Spectroscopic study of free only optically trapped nanoparticles ............................................ 61 Charge detection by electrostatic force microscopy in quantum devices ................................ 62 Suspended graphene and nanotubes for low temperature opto-electronics ............................. 63 Physicochemical characterization and image synthesis methods to generate photorealistic pictures of ancient materials ..................................................................................................... 64 New generation of phosphors for LED lighting prepared by sol-gel method .......................... 65 Pressure as a way to control the coupling between magnetic and electric properties .............. 66 La pression comme contrôle du couplage entre propriétés magnétiques et électriques ........... 67 Impact du soufre sur le comportement des platinoïdes dans les fluides géologiques .............. 68 Epitaxial Superconducting Quantum NanoWiresTexte sur une page avec figures pour la totalité du sujet de Master 2 en explicitant : ............................................................................. 69 Superconducting qubits ............................................................................................................ 70 Theory and experiments on magnetic skyrmions ..................................................................... 71 Long range electron-electron interactions and charge frustration ............................................ 72 Fluctuations hydrodynamique en conditions extrêmes ............................................................ 73 Turbulence Quantique : étude expérimentale ........................................................................... 74 Convection naturelle aux nombres de Rayleigh extrêmes ....................................................... 75 Mesure de fluctuations de vitesse par anémométrie à fibre optique ........................................ 76 Thermal expansion in rare-earth cage systems ........................................................................ 77 Molecular spin devices for quantum processing ...................................................................... 78 Cavitation at the nanoscale ....................................................................................................... 79 Functionalization of suspended thermoelectric nano-generators ............................................. 80 Superconducting Higgs mode .................................................................................................. 81 Study of the physical properties of new unconventional bidimensional superconductors under extreme conditions of pressure ................................................................................................. 82 Search for new high critical temperature superconductors ...................................................... 83 Superconducting Josephson junctions based on Van der Waals Heterostructures .................. 84 Superfluidity of light dressed with excitons in nanostructured semiconductor microcavity ... 85 Nanofils ferromagnétiques d’alliage à mémoire de forme Ni-Mn-X (x=In, Ga) ..................... 86

21

TeraHertz waves generation from phase-matched difference frequency conversion in non linear crystals ............................................................................................................................ 87 Probing the superfluid density in dichalcogenides superconductors ....................................... 88 Investigation of magnetization processes in R-M intermetallic compounds………………... 89 From engineering a half-open Floquet qu-bit to thermodynamics of topological effects in multi-terminal Josephson junctions ..................................................................................... 90

22



23

Magnetic Separation: a new route for material recycling

General Scope: The issue of so-called “critical” materials is crucial for the development of new technologies for energy (photovoltaic panels, magnets, batteries, etc...). In particular, rare earth (RE) elements are in the front line in Europe, because they combine both a very high supply risk together with a growing economic importance. In order to reduce the import pressure, it is necessary to develop a sustainable recycling process for Europe. To date, less than 1% of the rare earths are being recycled due to, amongst others, a lack of efficient and environmentally-friendly recycling technologies. In this subject, magnetic separation is presented as an alternative way to recycle RE-based scrap. As a physical separation method, magnetic sorting combines the advantage of being a robust, cost effective and environmentally-friendly technique. For magnetic separation purposes, HGMS devices (High Gradient Magnetic Separator) creating strong magnetic forces are developed at CNRS/Institut Néel. Your mission will be to conduct the experiments needed to demonstrate the recycling feasibility of various RE-based alloys. You will prepare powdered materials in view of the recycling process using various techniques based both on physics and chemistry, such as: dissolution, decomposition, milling, centrifugation, etc… You will perform tests of magnetic separation and finally characterize the final products (both from the magnetic and microstructural viewpoints) and exploit the results.

Research topic and facilities available You will benefit from the expertise of the TEMA group (Processing Elaboration Materials Applications, 6 persons) on the development of processes using intense magnetic fields, on the recycling processes as well as on the synthesis of alloys in various forms. Facilities available in the group include high superconducting magnets, various processing tools (induction cold crucible, furnaces, milling facilities, separation tools, etc…) and characterization devices (laser granulometry, ATD/TGA, microscopy, etc…). All common facilities from Institut Néel available as well (SEM, magnetic measurements, DRX, etc…) Possible collaboration and networking: This subject is part of the "Recup 'TR" project which deals with the recycling of Rare Earth elements contained in magnets and other Rare Earth based alloys. You will be involved with both academic and industrial contacts. Possible extension as a PhD: possible (a project with financial support for a PhD is forecast). Required skills: -Interest in the recycling and the valorization of by-products. -General curriculum with a specialty in Materials Science. -Autonomy, initiative and ability to work in a team and to adapt to a collaborative project, which includes partners from academic research and industry. -Knowledge in physicochemical processes and/or metallurgy is welcome. Starting date: Spring 2018 Contact: Sophie RIVOIRARD, Institut Néel - CNRS Phone:04 76 88 90 32 e-mail : [email protected] More information : http://neel.cnrs.fr, https://www.youtube.com/watch?v=QfLmRl44lG8



24

Coherent control of the spin of an individual magnetic atom with surface acoustic waves

Context : Individual spins in semiconductor nano-structures are promising for the development of quantum information technologies. Spin based quantum systems typically rely on resonant magnetic field to drive coherent transitions between different spin states. Although such magnetic driving has been effective, developing alternative modes of control opens new routes for coupling disparate quantum states to form hybrid quantum systems. Particularly useful examples are electric fields, optical fields and mechanical lattice vibrations. The last of these represents direct spin-phonon coupling which garner fundamental interest as a potential mediator of long-range interaction between remote solid state spin qubits. Thanks to their expected long coherence time, localized spins on individual magnetic atoms in a semiconductor host are an interesting media for storing quantum information. We recently demonstrated that the spin of an individual chromium atom (Cr) inserted in a quantum dot (QD) can be used as an optically addressable spin qubit with large intrinsic spin to strain coupling. Detailed project and means available: We want to exploit the spin to strain coupling of Cr to perform coherent mechanical driving of the spin of the atom. Controlled dynamical strain will be applied on Cr-doped QDs using surface acoustic waves (SAW). SAW, phonon-like excitations bound to the surface of a solid, are widely used in modern electronic devices but are also proposed as efficient quantum bus enabling long-range coupling of a wide range of qubits. During the internship, we will develop SAW based devices on Cr-doped QD samples. Inter-digitated piezo-electric transducer working in the GHz range will be designed, realized and tested. Optical measurements and comparison with a model will permit to estimate the amplitude of the oscillating strain applied on individual QDs. The next step will be to combine SAW excitation with existing resonant optical pumping technique to probe the influence of pulsed oscillating strain on the Cr coherent dynamics. Controlling the area of strain pulses, we will perform Rabi oscillations on the {+1;-1} Cr spin qubit (see figure). Sequences of !/2 pulses will also be used for Ramsey types experiments for a mechanical determination of the coherence of the {+1;-1} qubit. Our system should allow studying a single spin in the sought-after "strong driving" regime ("Rabi>#qubit) and thereby shed new light on this exciting, but still under-explored area of quantum physics.

Collaboration and networking: This work, mainly experimental, will be realized in the framework of the «NanoPhysique et Semi-Conducteurs» group (CNRS / Institut Néel & CEA / INAC). The student will work in interaction with people in charge of the growth of samples at the INAC in collaboration with the University of Tsukuba. He/she will have access to technology platforms (Nanofab, PTA) for the nano-fabrication and will be also involved in the modeling of the spin dynamics in the studied nano-structures. This project is funded by the ANR contract “MechaSpin” starting at the beginning of 2018. This internship can be followed by a PhD thesis on the same topic. Required profile: Master 2 (or engineering degree) with good knowledge in solid state physics (electrical, optical, magnetic, mechanical properties), quantum mechanics, optics, electronics. Foreseen start for the internship: March 2018 Contact: Lucien BESOMBES, Institut Néel ; 04 56 38 71 58 ; [email protected]



25

Hybrid nanowires for topological quantum computing General Scope : One interesting and promising proposal for quantum computation relies on the so called topological protected quantum bits. Realizing such quantum bits depends on the ability to make materials that can host Majorana bound states. In 2012, signatures of such states were reported in one-dimensional semiconductors with high spin-orbit coupling, coupled to a superconductor [1]. Since then, nanostructured hybrid materials based on superconductor/semiconductor interfaces have received increased attention. Yet, controlled formation of topological protected states can only be realized if the superconductor/semiconductor interface is of high quality. Creating those interfaces in an epitaxial fashion would have many advantages, among them better transparency, controlled interface chemistry, higher current injection and lower disorder. However, combining crystalline metals and semiconductors is challenging because of the fundamental different properties of both families of materials. Recently, in-situ epitaxial growth of InAs/Al core-shell nanowires exhibited defect free and homogeneous interfaces [2]. The devices revealed a superconducting hard gap demonstrating the high potential of in-situ shell epitaxy. Here, we propose to develop novel interfaces using a higher critical field superconductor such as vanadium to reach the Majorana regime and to perform further topological experiments. [1] V. Mourik et al 2012 Science 336(6084) 1003[2] P. Krogstrup et al 2015 Nature materials 14 400 Research topic and facilities available: In this project, the student will carry out the growth of networks of hybrid nanowires in a III-V molecular beam epitaxy reactor in CEA. In particular, she/he will focus on InAs/V core/shell nanowire fabricated using templates developed in the cleanroom. The student will perform the characterization of the samples by SEM, EDX and/or TEM. Together with partner labs, she/he will participate in low temperature measurement campaigns using a dilution fridge, as well as perform high-end structural studies using advanced equipment and facilities. Possible collaboration and networking: University of Pittsburgh (S. Frolov, M. Hatridge, D. Pekker) University of California in Santa Barbara (C. Palmstrom) LAAS Toulouse (S. Plissard) CEA-INAC (J. Meyer, M. Houzet, S. De Franceschi) Possible extension as a PhD: yes Required skills: Motivated experimentalist Programming Starting date: beginning of 2018 Contact: Name: Moïra Hocevar Institut Néel - CNRS Phone: 04 78 38 35 13 e-mail: [email protected] More information: http://neel.cnrs.fr

(a)

(b) (c)

Description of the internship methodology. (a) Growth. InAs nanowires will be grown by the VLS mechanism using gold catalysts. Then a shell of V will be fabricated by switching the growth mode to 2D growth. (b) Morphology. SEM image of a sample of InAs/Al nanowires with polycrystalline Al shells. (c) Structure. TEM image of a hybrid Si/III-V core-shell nanowire.



26

Image of an InAs-on-GaAs nanowire taken by transmission electron microscope (scale bar 100 nm). The dark droplet at the top is the gold catalyst. Inset: image of a standing nanowire from the same sample taken by scanning electron micrograph (scale bar 200 nm, 30° tilt).

Single photon sources based on quantum dot semiconductor nanowires General Scope : Single-photon sources are key devices for emerging quantum technologies. They are a necessary building block for quantum-secure communication networks and for photonic quantum computing. In addition, a bright single-photon emitter has also potential applications in light flux metrology, as a new standard of luminous intensity (the so-called ‘quantum candela’). Despite an intense research effort, the community still lacks an efficient and reliable single-photon emitter operating in the telecom windows (centered between 1.3µm and 1.5µm). Most promising candidates are based on artificial atoms such as fluorescent atomic defects or quantum dots. In particular, semiconductor quantum dots are stable emitters that can be integrated on chip. Defining a quantum dot in a nanowire is very promising, as the light extraction efficiency reaches 90% and the quantum dot morphology can be controlled to the nanometer scale by fine tuning the growth parameters [1]. In our team, we focus on the fabrication and optical characterization of InGaAs quantum dots integrated in GaAs nanowires using the vapour liquid solid mechanism. We lately demonstrated that we can grow axial GaAs/InGaAs heterostructures in a nanowire without creating any crystalline defects [2]. [1] J Claudon et al 2010 Nature Photonics 4(3) 174 [2] D V Beznasyuk et al 2017 Nanotechnology 28 365602 Research topic and facilities available: In this project, the student will (1) grow quantum dot nanowires based on III-V compound semiconductors by molecular beam epitaxy reactor in CEA. The nanowires will be fabricated from Au nanoparticles ordered within a pattern designed by electron beam lithography in the cleanroom facility of Institut Néel. The nanowires will be studied by electron microscopy at the Advanced Nanocharacterization Platform in CEA. She/he will also (2) study the optical properties of these nanowires using micro photoluminescence at cryogenic temperatures. Possible collaboration and networking: CEA-INAC Grenoble (J. Claudon, J. Bleuze) ILM Lyon (P. Verlot) Philips Eindhoven (M. Verheijen) Possible extension as a PhD: yes Required skills: Motivated experimentalist Programming Starting date: beginning of 2018 Contact: Name: Moïra Hocevar Institut Néel - CNRS Phone: 04 78 38 35 13 e-mail: [email protected] More information: http://neel.cnrs.fr



27

Artificial frustrated spin systems General Scope : In physics as in chemistry, it is generally accepted that matter orders, like in a crystalline solid, when cooled at sufficiently low temperature. There also exist systems that remain disordered in the manner of a gas or a liquid, even at the lowest temperatures accessible experimentally. What is much more rare is a state of matter that would be both ordered and disordered everywhere in the system, i.e. that would be both solid and liquid for example. Such a phase, “liquid” and “solid” at the same time, has been observed recently in our group, in an artificial magnetic system made of elongated nanomagnets arranged as a lattice of equilateral triangles connected by their corners (kagome lattice) [1]. This unusual state of matter is distinctly different than the magnetic equivalent of a glass of water containing ice cubes, which would be, simply, a system presenting the coexistence of two physically separated phases, out of thermodynamic equilibrium. Here instead, we have demonstrated, in an artificial system, the magnetic equivalent of both liquid and crystalline phases at any time, without being phase separated [1]. More generally, artificial magnetic systems offer the opportunity to explore intriguing and fascinating phenomena in condensed matter physics and constitute a formidable playground to test experimentally many different theoretical predictions. For example, we also fabricated for the first time a peculiar disordered magnetic state on a square lattice that was predicted back in the sixties, but never observed experimentally [2]. This system is interesting as it is characterized by a finite entropy, even at zero temperature, thus (apparently) violating the third law of thermodynamics. Besides, excitations in this square system behave as classical analogues of magnetic monopoles, thus (apparently) contradicting what we learn from magnetostatics. We now would like to go a step further and investigate some of the exotic properties predicted in these two systems. Research topic and facilities available: The main objective of this internship is to explore possible new states of matter in kagome and square arrays of nanomagnets. Some properties have been predicted but never observed experimentally. The goal of this internship is to image these states and their associated properties in real space, using magnetic imaging techniques available in the lab. The student will be involved in the design of the artificial magnetic systems based on nanofabrication techniques also available in the lab.

(left) Schematics of the artificial square system we studied. (right) Topographic (top) and magnetic (bottom) images of an experimental realization of an artificial square system characterized by a finite entropy at low temperature and monopole-like excitations. From Ref. 2.

Possible collaboration and networking: The student will be working within the Micro- and Nano-Magnetism (MNM) team of the Néel Institute. He/she will collaborate closely with researchers of other groups (TMC) and work with the technical staff of the laboratory (MFM platform, Nanofab). [1] B. Canals et al., Nature Communications 7, 11446 (2016). [2] Y. Perrin, B. Canals and N. Rougemaille, Nature 540, 410 (2016). Possible extension as a PhD: This internship is meant to be followed by a PhD thesis (a 3 years funding is already available through an ANR project that will start in 2018). Required skills: nanosciences, nanophysics. condensed matter physics. Starting date: March 2018 Contact: Name: Rougemaille Nicolas - Institut Néel - CNRS Phone: 04 76 88 74 27, e-mail: [email protected], More information: http://neel.cnrs.fr



28

Superconductivity in atomic-scale magnetic nanostructures

Nanometer scale scatterers (a single atom, a molecule, a quantum dot or an atomic nanowire) can interact with a superconducting condensate via potential scattering and/or magnetic exchange coupling. This leads to bound states, at energies below the superconducting gap, with peculiar spatial and spectral properties [1]. In particular, these states can be topologically trivial (the case of so-called Shiba states) or not (predicted Majorana zero modes). The ability of electrons to tunnel between two conductors is extremely sensitive to both distance and density of states. This has made scanning tunneling microscopy/spectroscopy (STM/STS) an extremely sensitive and versatile tool to visualize atomic scale topographic features and variations in the local density of states. Using low temperature STM, we will investigate the signatures of magnetic interactions and possible topological superconductivity in a range of novel combinations of superconductors and magnetic nano-objects. By using superconducting tips, we will be able to combine at the same location tunneling experiments involving single electrons (standard tunneling spectroscopy) and Cooper pairs (Josephson current spectroscopy). This will be possible owing to the unique milliKelvin STM operation capability available in the Grenoble host group [2]. This project will be carried out using a low temperature STM operating at 100 mK, at Institut Néel [1]. Part of the experiments will be performed in the group of K. Franke (Berlin), in a low temperature STM with complementary capabilities [2]. The student’s work will encompass:

- Setting up a new ultra-high vacuum surface preparation chamber - Preparing magnetic nanostructures by self-assembly or single-atom manipulation - Performing low temperature scanning probe measurements - Theoretical analysis and interpretation

[1] Magnetic anisotropy in Shiba bound states across a quantum phase transition, N. Hatter, B. W. Heinrich, M. Ruby, J. I. Pascual, K. J. Franke, Nature Comm. 6, 8988 (2015). [2] Charge Puddles in Graphene Near the Dirac Point, S. Samaddar, I. Yudhistira, S. Adam, H. Courtois, and C. B. Winkelmann, Phys. Rev. Lett. 116, 126804 (2016). Interactions and collaborations This project will be carried out in tight collaboration with the group of K. Franke (Berlin) and complementary experiments will be carried out at both laboratories. Analysis and interpretation will benefit from strong local theoretical support in Grenoble and Berlin. Possible extension as a PhD: Yes Required skills: Master level (ongoing) or equivalent in Physics , with focus on condensed matter, quantum physics, or nanophysics. Starting date: beginning of 2018 Contact : [email protected], [email protected] Institut Néel - CNRS : 04 76 88 78 36, 04 76 88 11 51 Plus d'informations sur : http://neel.cnrs.fr/spip.php?rubrique49

Spatial map of a low-energy bound state around a Fe nanoisland on super-conducting Pb and sketch of STM experiment.



29

Quantum electronic transport probed by thermoelectricity The flow of heat at the microscopic level is a fundamentally important issue, in particular, if it can be converted into free energy via thermoelectric effects. While the understanding of quantum charge transport in nanoelectronic devices has reached a great level of maturity, heat transport and thermoelectricity experiments are lagging behind. Heat transport and thermo-electricity can nevertheless give insight to new phenomena that charge transport is blind to. In most macroscopic conductors, heat- and charge conductances are simply proportional. This is called the Wiedemann-Franz law. Our group recently demonstrated strong deviations (up to 300 %) from this law in a single-electron transistor (SET) at very low temperatures [1], due to the strong electron interactions in the SET. Building on these findings, we seek for novel signatures of electron interactions and quantum coherent effects in the thermoelectric properties of single quantum dot junctions. We will study the heat dissipation in the leads due to sequential and higher-order tunneling events. We will further determine the signatures of cotunneling and Kondo-correlations in the thermoelectric properties of a single quantum-dot junction. This project will be carried out using an existing dilution refrigerated ultra-low noise transport experiment operating below 30 mK at Institut Néel. Quantum dot junctions based on single molecules or metallic nanoparticles will be formed using the electromigration technique [2]. The graduate student’s work will encompass in particular:

- Cleanroom nanofabrication (e-beam lithography, thin film deposition, …) of devices - Very low temperature charge transport and thermoelectric measurements - Theoretical analysis and interpretation

[1] Thermal Conductance of a Single-Electron Transistor, B. Dutta, J. T. Peltonen, D. S. Antonenko, M. Meschke, M. A. Skvortsov, B. Kubala, J. König, C. B. Winkelmann, H. Courtois, and J. P. Pekola, Phys. Rev. Lett. 119, 077701 (2017). [2] Superconductivity in a single-C60 transistor, C. B. Winkelmann, N. Roch, W. Wernsdorfer, V. Bouchiat, and F. Balestro. Nature Physics 5, 876 (2009). Interactions and collaborations This project is supported by a European Research Network funding and will be carried out in tight collaboration with the group of J. Pekola (Helsinki). Analysis and interpretation will benefit from strong local theoretical support in Grenoble (D. Basko). Possible extension as a PhD: Yes Required skills: Master level (ongoing) or equivalent in Physics , with focus on condensed matter, quantum physics, or nanophysics. Starting date: beginning of 2018 Contact : [email protected], [email protected] Institut Néel - CNRS : 04 76 88 78 36, 04 76 88 11 51 Plus d'informations sur : http://neel.cnrs.fr/spip.php?rubrique49

Top: nanofabricated heat transport measurement device. The SET island is shown in yellow; local temperature probes are in cyan. Bottom left : SET charge conductance data as a function of bias and gate voltages, showing gate-controllable Coulomb blockade. Bottom right: heat transport through the SET is qualitatively similar to charge transport, but quantitatively very different.



30

Monochromatic on-demand single-electron source

When inserting a single quantum dot (QD, which can be a molecule or a nanoparticle) between two superconducting (S) contacts, the resulting device has fascinating electronic conduction properties, which reflect the coupling of discrete orbital quantum energy levels to superconductivity [1]. We have recently demonstrated the dynamical properties of such devices, which show up when the QD chemical potential is changing rapidly in time [2]. In particular, the probability and direction of tunneling of individual electrons can be very precisely tuned. With S-QD-S junctions, we have built a quantum metrological electron source producing a quantized current. Furthermore, the on-demand electrons can in principle be injected at very precisely determined energies. However, so far we have only indirect evidence of the monochromaticity (defined energy) of the single-electron source. The goal of this Master/PhD project is to couple the single-electron source to an on-chip superconducting bolometer. This will allow performing time-resolved detection of the heat released by individually injected electrons. Such bolometers consist of a superconducting resonator coupled to tunnel junction [3]. The resonator frequency strongly depends on the tunnel junction impedance, which itself depends on the local temperature. The dispersive resonator read-out allows thus for rapid detection of small energies.

This project will be carried out using an existing dilution-refrigerated ultra-low noise transport experiment operating at 50 mK at Institut Néel. The graduate student’s work will encompass:

- Cleanroom nanofabrication (e-beam lithography, thin film deposition, …) of devices - Setting up the resonator radio-frequency read-out (coaxial lines, filters, amplifiers, …) - Very low temperature dc and ac transport measurements - Theoretical analysis and interpretation

[1] Superconductivity in a single-C60 transistor, C. B. Winkelmann et al., Nature Physics 5, 876 (2009). [2] Single Quantum Level Electron Turnstile, D. M. T. van Zanten et al., Phys. Rev. Lett. 116, 166801 (2016). [3] Incomplete measurement of work in a dissipative two level system, K. L. Viisanen et al., New J. Phys. 17, 055014. Interactions and collaborations This project is supported by a European Research Network funding and will be carried out in tight collaboration with the group of J. Pekola (Helsinki). Analysis and interpretation will benefit from strong local theoretical support in Grenoble (D. Basko). Possible extension as a PhD: Yes Required skills: Master level (ongoing) or equivalent in Physics , with focus on condensed matter, quantum physics, or nanophysics. Starting date: beginning of 2018 Contact : [email protected], [email protected] Institut Néel - CNRS : 04 76 88 78 36, 04 76 88 11 51 Plus d'informations sur : http://neel.cnrs.fr/spip.php?rubrique49

(a) SEM image of superconducting break-junction, in which the QD is inserted. (b) Energy diagram of S-QD-S device showing possible electron tunneling events. (c) Current map of device. A trajectory of (VB,VG) along the line shown allows exactly one electron to be transferred across the device.



31

Spin-orbitronics mediated by one-atom-thin graphene General Scope : Next generation storage media will presumably rely on the manipulation of magnetisation with an electric current. IBM foresees so-called racetrack memories exploiting this effect, performing faster than current technology and with low energy consumption. The elementary bits of information in this emerging class of spintronic devices are carried by nanometer-sized magnetic objects — domain walls and skyrmions. These objects are in fact topological defects, whose chirality provides a channel where to encode information in a very robust way. To reach the smallest bit sizes (hence the highest storage density) and control chirality via the spin-orbit interaction, nanometer-thin magnetic current lines with magnetisation perpendicular to the line and specific lattice symmetry are needed. Graphene, the atomically-thin carbon crystal, is especially promising in these respects when top-contacted to a thin ferromagnet metal back-contacted with a heavy metal (see figure), as we and our collaborators have shown in the past 5 years.* Research topic and facilities available: The purpose of the internship is to implement, for the first time, high-quality sandwiched structures into lab-scale spintronics devices, consisting of nanometer-scale tracks flown by spin-polarised electrical currents. The sandwiches will be produced with atomically-sharp interfaces between graphene and metallic ultra-thin layers thanks to atomic and

molecular beam deposition. Nanofabrication techniques will be used to shape the devices. Magnetic imaging will serve to image the magnetic topological defects inside the tracks and understand their shape and interaction with other defects. The work will exploit state-of-the-art materials deposition machines and lithography, and will make use of optical and scanning probe magnetic microscopies.

Possible collaboration and networking: The work planned will benefit from existing collaborations with colleague theorists performing ab initio calculations in Grenoble. We expect that the devices that will be developed will then be investigated with high resolution magnetic microscopes exploiting the X-ray beams available at synchrotron facilities. Possible extension as a PhD: The internship is envisaged as the key prelude to more advanced works within a Ph.D project, to start in Fall 2018. Among other things, the Ph.D project will address the spatio-temporal evolution of the magnetic topological defects, with time-resolved and/or vectorial magnetic microscopy observations as central approaches. Unique instruments installed at synchrotron facilities and at LBNL Berkeley will be used for that purpose. Required skills: A solid background in condensed-matter physics is crucial. A personal interest for sophisticated instrumentation is recommended. Starting date: March, 2018 Contact: Name: Johann Coraux, Nicolas Rougemaille Institut Néel - CNRS Phone: +33 4 7688 1289 e-mail: [email protected] - [email protected] More information: http://neel.cnrs.fr * J. Coraux, N. Rougemaille & coworkers, Journal of Physical Chemistry Letters vol. 3, p. 2059 (2012); Applied Physics Letters vol. 101, p. 142403 (2012); Applied Physics Letters vol. 104, p. 101602 (2014); Carbon vol. 94, p. 554 (2015); Nano Letters vol. 16, p. 145 (2016); Scientific Reports vol. 6, p. 24783 (2016).



32

Triplet photon generation in optical non linear waveguides General Scope : This position concerns Triple Photons Generation (TPG). It is based on a third order nonlinear optical interaction is the most direct way to produce pure quantum states of light, called three-photons states.

These states exhibit three-body quantum entanglement and their statistics go beyond the usual Gaussian statistics relevant to coherent sources and optical parametric twin-photon generators, offering thus outstanding potential applications in the field of quantum information. Undoubtedly, three-photons states are new quantum tools to study the non-intuitive properties of quantum mechanics. In 2004, we made the first experimental demonstration of a pure TPG [Opt. Lett. 29, 2794-2796 (2004)], which means that the three photons were created from a single one, using a two-wave stimulation scheme in a phase-matched KTiOPO4 (KTP) bulk crystal. This pioneer work has opened new exciting opportunities in quantum optics. We made the classical and quantum theory of TPG [J. Opt. Soc. Am. B 25(1), 98 – 102 (2008) ; Phys. Rev. A, 85(4) 02389 1-12 (2012); invited conference at IEEE IPC San Diego 15 October 2014]. Research topic and facilities available: TPG was first performed in a bulk crystal, which was possible only by stimulated the process using two modes of the field. We have then proposed a novel approach for spontaneous TPG in a guided configuration based on a conventional glass fiber [Opt. Lett. 26(15), 3000-3002 (2011) ; Opt. Lett., 40(6), 982 (2015) ; invited conference at Non Linear Optics, Hawaii, 27 July 2015]. TPG can benefit from both strong confinement and long interaction length. This result is very important since it indicates that an optical waveguide can enable to achieve a spontaneous TPG, which is completely impossible using a bulk medium. However, because the phase matching is only possible in an optical fiber between two different modes of propagation with a poor spatial overlap, the efficiency of TPG is expected to be very poor (about one triplet/s in a 10 meters long fiber) The work that is proposed in the framework of this internship is to combine the benefit of the high non linearity of bulk crystals such as KTP and the long interaction length and the strong confinement of an optical waveguide [Opt. Exp., 24(9), 9932(2016)]. It will be based on a ridge waveguide cut in a KTP bulk crystal (typically, a section of 10x10 µm2 and a length of about two centimeters). After the first experiments that have been performed recently on second and third harmonic generation in ridge waveguides, we intend to begin TPG experiments in new ridges with new propagation direction. Possible collaboration and networking: Collaboration with : FemtoST (Besançon), Laboratoire de Physique et Nanostructures (Marcoussis), GAP (Université de Genève). Possible extension as a PhD: Yes Required skills: A background in laser optics, non-linear optics, quantum mechanics or quantum optics will be useful for the purpose of the project. Starting date: starting from february or march 2018 Contact: B. Boulanger ([email protected]), V. Boutou ([email protected]) Institut Néel - CNRS : tél 0476887807 / 0476887410 More information: http://neel.cnrs.fr



33

Garnet nanocrystals for white LEDs General Scope : Lighting accounts for about 20% of the global building electricity consumption. A typical wLED combines a blue LED chip (typically InGaN, emitting around 450 nm) with a micron-sized luminescent powder, called phosphor, encapsulated into an epoxy resin (Figure 1a). The commonly-used phosphor material is Y3Al5O12 doped Ce3+, labeled YAG:Ce, presenting a high internal luminescence quantum yield (iQY > 85%), a perfect photostability and good, though not perfect, spectroscopic properties (!exc = 450 nm and !em = 550 nm). Although wLEDs are commercially available, they present two main drawbacks: (1) due to the micron size of YAG:Ce, blue and yellow light beams can be backscattered towards the chip, which can thus be gradually deteriorated. As a consequence, the external quantum efficiency (EQE) of a wLED device is limited to ~ 70%. (2) LEDs provide a so-called “cold white light”, which can be detrimental for the eyes, due to the yellow-centered emission of YAG:Ce. To overcome these drawbacks, we are developing original nanometer-sized phosphors, which present an emission shifted towards the red range (Figure 1b). The proposed internship is part of this project. Research topic and facilities available: The goal of this project is to develop original garnet phases such as Ce-doped Y3Al5-xCrxO12 or Gd3Sc2Al3O12 at the nanoscale, using solvothermal processes. The challenge will be to control the particle size and their optical properties in terms of emission range, quantum yield and photostability. Sovothermal syntheses will be performed at the Institut Néel, where the equipment is available. The obtained materials will be fully characterized at the Institut Néel by XRD, electronic microscopy (SEM and TEM), luminescence and quantum yield measurements. Possible collaboration and networking: Time-resolved spectroscopy will be carried out at the Institut Lumière Matière (ILM, Lyon). Possible extension as a PhD: Yes Required skills: Good skills in Materials Sciences (chemical synthesis, characterization techniques: XRD, SEM) Starting date: March 2017 Contact: Name: Géraldine DANTELLE Institut Néel - CNRS Phone: 04 76 88 10 44 e-mail: [email protected] More information: http://neel.cnrs.fr

Figure 1: (a) Simplified scheme of a commercial LED (b) Proposed geometry for enhanced external efficiency and improved ageing properties.

"#$! "%$!



34

Recherche de la supraconductivité dans des bi-couches de graphène sous haute pression

Cadre général : La multiplication des études sur le graphène a ouvert la voie vers un grand nombre des nouvelles applications. Cependant très peu d'études expérimentales ont été réalisés sur ses propriétés électroniques lorsque il est placé sous haute pression. Il est vrai que étant extrêmement dur dans le plan basal, peu des changements sont attendus sur le graphène monocouche. Mais la physique des bi-couches sous pression risque d'être très riche. La liaison Van-der-Waals entre deux couches de graphène est très faible et doit être très sensible à la mise en pression. Un empilement symétrique du type A-A forcera une liaison inter-couches entre atomes de carbones. La bi-couche de carbone sera déformée vers une symétrie sp3, du type diamant ou silicène. Or des calculs théoriques récents [F. Liu et al., Phys.Rev. Lett. 111(2013)066804] prédissent une supraconductivité chirale dans des bi-couches de silicène, ainsi que d'autres propriétés supraconductrices anormales. La transformation sous pression vers une bi-couche "frippé" de type silicène risque d'être permanente et irréversible, conduissant à des réelles possibilités des nouvelles applications Sujet exact, moyens disponibles : Le sujet du stage consistera dans une première étape dans la fabrication de bi-couches de graphène, déjà mise au point dans l'Equipe HYBRIDE par V. Bouchiat, et leur adaptation pour son montage dans les cellules d'haute pression (déjà testée). Ensuite se feront des mesures de transport en fonction de la température jusqu'à 1K dans des cellules de pression pouvant atteindre les 30GPa avec M. Nunez-Regueiro de l'Equipe MagSup, d'une grande expérience dans l'étude des composés carbonés et supraconducteurs sous pression. Interactions et collaborations éventuelles : L'étudiant(e) sera amené(e) à collaborer avec des collègues des différentes équipes de l'IN.

Ce stage pourra se poursuivre par une thèse. Formation / Compétences : Une bonne connaissance de la physique de la matière condensée est souhaitée. Période envisagée pour le début du stage : Contact : Nom Prénom Nunez-Regueiro, Manuel ; [email protected] ; tél.: 0476887838 Bouchiat, Vincent ; [email protected] ; tél.: 0476881020 Institut Néel - CNRS Plus d'informations sur : http://neel.cnrs.fr



35

Étude de la compétition sous haute pression entre les ordres de charge et la supraconductivité dans les cuprates de mercure à haute température critique

Cadre général : L'origine de la interaction responsable de la supraconductivité à haute température critique (SHTC) continue à être un sujet extrêmement controversé. Depuis quelques années l'on a observé dans la plupart les familles de cuprates SHTC l'existence des ordres de charge (OC) en compétition avec la supraconductivité. Ils ont été observés dans la région sous-dopée du diagramme de phase des cuprates SHTC en coïncidence avec le, encore incompris, pseudo-gap. Ce fait semblait suggérer que leur étude pourrait apporter une nouvelle clé pour la compréhension du problème. En particulier, il est question de déterminer si ces ordres de OC sont intrinsèques a la physique des SHTC. Tout récemment nous nous sommes attaqués à l'étude des nouveaux monocristaux de haute qualité de cuprates de mercure, ceux même dont le record de température critique, Tc=166K à 26GPa, a été signalé par notre laboratoire (EPL72[2005]458). Étonnement, nous avons observé le OC sous une pression de 10GPa dans la région sur-dopée du diagramme de phase (voir figure; soumis Science). Dans cette région, le matériau est un liquide de Fermi normal et aucune propriété exceptionnelle, pouvant être reliée à la physique anomale des SHTC, n'est attendue. Ceci met en question l'hypothèse de l'importance du OC pour les SHTC. Cependant, il faut faire une étude complète des cristaux avec différents taux de dopage pour cerner clairement le comportement de ces matériaux sous haute pression. Cette étude est le sujet de ce stage pouvant être continué en thèse. !Sujet exact, moyens disponibles : Le candidat fera des mesures de résistance électrique sous haute pression en fonction de la température pour déterminer l'évolution des propriétés de transport et de la supraconductivité dans de monocristaux de cuprates de mercure Hg-1201 avec différents taux de dopage (en collaboration avec Dorothée Colson, Service de Physique de l'État Condensé DSM/IRAMIS/SPEC, CEA Saclay). De cette manière il pourra observer comment la concentration de porteurs affecte l'apparition du OC sous pression. Il participera à des mesures de diffraction par rayons X réalisées à l'ESRF sous les mêmes monocristaux en collaboration avec G. Garbarino. La corrélation entre le deux types de mesure aidera à déceler si le OC est en effet une propriété du pseudo-gap et essentielle a la SHTC, ou un phénomène indépendant du mécanisme de la SHTC. Interactions et collaborations éventuelles : L'étudiant(e) sera amené(e) à collaborer avec des collègues du laboratoire de fabrication des échantillons, ainsi qu'avec les responsables de la ligne haute pression de l'ESRF dans le cadre des expériences de diffraction X. Ce stage pourra se poursuivre par une thèse. Formation / Compétences : Une bonne connaissance de la physique de la matière condensée est souhaitée. Période envisagée pour le début du stage : Contact : Nom Prénom Nunez-Regueiro, Manuel ; [email protected] ; tél.: 0476887838 Institut Néel - CNRS Plus d'informations sur : http://neel.cnrs.fr



36

Recherche de nouveaux supraconducteurs à haute température critique Cadre général : La supraconductivité non-conventionnelle à haute température critique apparait lorsqu’un composé bidimensionnel ayant un ordre antiferromagnétique avec une température de Néel (TN) élevé et un faible moment magnétique est dopé. Ceci est le lié à la forte interaction d'échange, responsable de l'antiferromagnétisme mais aussi de la supraconductivité. En particulier c'est le cas des cuprates et des chalocgénures et arséniures de fer. Donc une stratégie raisonnable pour chercher des nouveaux supraconducteurs non-conventionnels à haute température critique est de sélectionner des matériaux présentant ces propriétés, les synthétiser et les doper. En particulier les composés au chrome sont connus pour avoir un antiferromagnétisme fort. Ceux ayant en plus une basse dimensionnalité sont difficiles à synthétiser, ce qui est un obstacle important, mais qui nous permet aussi d'être les parmi les premiers à les étudier pour comprendre leur physique. Celle-ci peut être très riche, indépendamment du fait de l’obtention de la supraconductivité ou non (effet Kondo Orbital dans CrSe2 [1]; Fluctuations quantiques à 600 K dans CrRe [2].) Même s’il y a quelques années, songer à trouver de la supraconductivité dans des composés au chrome rendait les experts sceptiques, sa découverte dans CrAs sous pression [3], permet maintenant d’élargir ce type d'étude. Sujet exact, moyens disponibles : Nous proposons en premier lieu d'essayer le dopage de composés type Ruddelsden-Popper Æn+1CrnO3n+1 (où Æ est un alcalino-terreux; voir figure). Nous avons déjà synthétisé les phases mères n=1, 2 et 3, et nous avons compris, grâce à des interactions entre expérimentateurs et théoriciens, leur physique. La synthèse de ces oxydes se fait à haute pression et haute température, en profitant de l’infrastructure très performante du laboratoire. Les propriétés cristallographique, électrique, magnétique, ainsi que la chaleur spécifique et l'expansion thermique seront sondés grâce aux différents appareils de caractérisation dont dispose l’Institut Néel. Des mesures sous très haute pression complèteront l’étude. Interactions et collaborations éventuelles : Des mesures utilisant la diffusion des neutrons (ILL) et ou des rayons X sur synchrotron (ESRF) seront aussi nécessaires à moyen terme pour comprendre l’ensemble des propriétés. D'autre part, ce sujet bénéficiera des interactions avec les théoriciens de l'Institut Néel ou de l'étranger. Ce stage pourra se poursuivre par une thèse (ou ce sujet est limité à un stage M2...): Oui. Formation / Compétences : Une bonne connaissance de la physique de la matière condensée est souhaitée. Période envisagée pour le début du stage : mars-avril 2017. Contact : Núñez-Regueiro, Manuel MCBT/Institut Néel - CNRS : tél 04 76 88 78 38 mel [email protected] Toulemonde, Pierre PLUM/Institut Néel - CNRS : tél 04 76 88 74 21 mel [email protected] Plus d'informations sur : http://neel.cnrs.fr [1] M. Núñez et al. Phys. Rev. B. 88 [2013] 245129. [2] D. Freitas et al. Phys. Rev. B. 92 [2015] 205123. [3] Wu Wei et al. Nature Comm.5 [2014] 5508.



37

Synthèse et caractérisation structurale de nouvelles ferrites de Ba/Bi Cadre général : Les matériaux multiferroiques possèdent la propriété unique de présenter simultanément plusieurs ordres ferroïques tels que les ordres ferromagnétiques (polarisation magnétique ou aimantation), ferroélectriques (polarisation électrique) et ferroélastiques (déformation mécanique). Les multiferroiques qui suscitent le plus d’intérêt sont les magnétoélectriques (ferroélectrique et ferromagnétique) et par extension les ferroélectriques et antiferromagnétiques. Peu de composés présentent de manière intrinsèque ces propriétés et la recherche de nouvelles phases couplée à l’étude de leurs propriétés est un vrai défi en matière condensée. Sujet exact, moyens disponibles : Le composé BiFeO3, ferroélectrique en dessous de 1100K et antiferromagnétique en dessous de 600K, fait partie de ceux les plus étudiés. Les composés au fer sont effectivement de bons candidats pour leurs propriétés magnétiques, et dans ce cadre nous envisageons d’explorer le diagramme pseudo ternaire BaO-BiO1.5-FeO1.5 dans sa partie riche en fer, qui a été pas ou peu explorée auparavant, afin d’en isoler de nouvelles phases à propriétés structurales et physiques originales. La technique d’élaboration des nouveaux matériaux utilisée sera la synthèse par voie solide, alliée à des techniques plus originales comme l’application de hautes pressions - hautes températures (presses gros volumes à l’Institut Néel). Ces méthodes de synthèse devraient ouvrir la voie à la découverte de nouvelles charpentes structurales. La caractérisation structurale fine sera une partie importante du stage et sera réalisée en combinant les méthodes de diffraction des rayons X sur poudre (affinements de Rietveld) et de Microscopie Electronique en Transmission (diffraction électronique et imagerie). Interactions et collaborations éventuelles : avec le personnel compétent en synthèse haute pression, et autres membres de l’équipe. Ce stage pourra se poursuivre par une thèse (ou ce sujet est limité à un stage M2...). Oui, par demande de bourse de thèse auprès de l’école doctorale Formation / Compétences : M2 dans le domaine des matériaux. Intérêts pour l’élaboration de nouveaux matériaux, la cristallographie et la diffraction des rayons X. Période envisagée pour le début du stage : à partir de janvier 2018 Contact : Lepoittevin Christophe Institut Néel - CNRS : 04 76 88 71 92 [email protected]



38

Circuit-QED: amplification at the single-photon level General Scope : During the last decade, it has been demonstrated that superconducting Josephson circuits behave as quantum bits and are very well suited to realize advanced quantum mechanical experiments. These circuits appear as artificial atoms whose properties are defined by their electronic characteristics (capacitance, inductance and tunnel barrier). Moreover, given their mesoscopic size, these quantum bits couple very strongly to electromagnetic radiations in the microwave range. Thus, it is now possible to perform quantum optics experiments using microwave photons and to unravel light-matter interactions using circuits. This field is dubbed circuit-QED (Quantum Electro-Dynamics). Measuring these microwave photons with very high quantum efficiency remains a tremendous challenge, since the energy conveyed by one single microwave photon is hundreds thousand times smaller than the one of usual optical photons. Yet signals at the single-photon level can be measured using Josephson parametric amplifiers [1]. In our team we are now using superconducting metamaterials (see figure) to engineer the next generation of parametric amplifiers [2]. These new devices allow us to explore the quantum limits of amplification as well as to perform quantum optics experiments. [1] Widely Tunable, Nondegenerate Three-Wave Mixing Microwave Device Operating near the Quantum Limit, N. Roch, et al. , Phys. Rev. Lett. 108, 147701 (2012). [2] L. Planat. , et al. , in preparation (2017). Research topic and facilities available: Our team has a strong experience in nanofabrication, microwave electronics and cryogenic equipment. First, the student will be in charge of the theoretical modeling of the superconducting parametric amplifier. She/He will then carry out the measurements of the device at very low temperature (30mK), using one of the three fully equipped dilution refrigerators of the team. The devices are fabricated in the clean room of the Neel Institute (Nanofab). If the candidate is interested in learning these fabrication techniques, she/he can be associated to this part of the project. Possible collaboration and networking: Our team is part of several national and international networks. For this specific project we are collaborating closely with Prof. K. Murch at Washington University in Saint-Louis, Missouri, USA, Prof. R. Vijay at TIFR, Mumbai, India, and Prof. I. Pop at KIT, Karlsruhe, Germany. This internship can be pursued toward a PhD Required skills: Master 2 or Engineering degree. We are seeking motivated students who want to take part to a state of the art experiment and put some efforts in the theoretical understanding of quantum effects in Josephson parametric amplifiers. Starting date: Flexible Contact: ROCH Nicolas Institut Néel - CNRS : phone: +33 4 56 38 71 77 email: [email protected] More information : http://neel.cnrs.fr & http://perso.neel.cnrs.fr/nicolas.roch

SEM image of a metamaterial-based Josephson parametric amplifier. The metamaterial is made of 70 SQUIDs as shown in the inset. From [2]



39

Quantum modeling of nano-structured solar cells General Scope : Nowadays, because of growing energy demand, exhaustion of oil resources, and global warming issues, the world is in need of alternative energy sources. Solar energy is one of the clean, renewable and available energy sources and great attention is given to new solar cells concepts based in particular on nanostructures or molecular systems. Research topic and facilities available: The development of new type of solar cells requires an accurate, reliable and comprehensive simulation of the designed structures. Theoretical modeling of such systems has been a challenging task for several years and we have developed a new simple non-equilibrium quantum formalism. This approach can be applied to two level models of photo-cells (see figure) and current efforts includes its application to more realistic models of molecular photocells or quantum dots. During its internship the student will learn basic aspects of the formalism which relies on the quantum scattering theory. He /she will participate to comprehensive simulation for simple models of nanosized solar cells. The student must be able to use Fortran codes. Computational ressources are available at Institut Néel.

Figure: Two level model. The photon is absorbed in the central part (molecule/ quantum dot) and creates an electron in the upper level and a hole in the lower level. The electron (hole) can be evacuated through the right (left) lead. The net result of the absorption of a photon is the transfer of an electron from the left to the right lead. Possible collaboration and networking: Currently, we have strong collaborations with scientific groups from Canada, USA and Iran. Possible extension as a PhD: The formalism developed in the team is new and opens an active area for many years. The student can continue this subject as a PhD thesis. Required skills: Quantum mechanics - Programming and analysis skills and having teamwork abilities. Starting date: March or April 2018 Contact : Mayou Didier Institut Néel - CNRS Phone : 04 76 88 74 66 email : [email protected] More information: http://neel.cnrs



40

Coupling a single quantum dot to a mechanical oscillator General Scope : Owing to the recent progress in nanotechnology and in ultra-sensitive motion detection methods, it becomes now possible to associate quantum systems such as superconducting qubits, spins, atoms or quantum dots to mechanical oscillators. The issue of these hybrid systems is to transfer the quantum properties of a two-level system to a mechanical oscillator, opening the possibility of storing quantum information on mechanical degrees of freedom. A few years ago, we have realized such an hybrid system made of a vibrating wire and a semi-conducting quantum dot1,2. The very large coupling between these two subsystems relies on mechanical strain (cf figure). The quantum dot undergoes periodic strain as the wire oscillates along its fundamental flexural mode at around 500 kHz. The alternatively tensile and compressive strain periodically alters the quantum dot energy levels and therefore the spectral position of the photoluminescence lines. Research topic and facilities available: We want to explore the reverse aspect of this coupling by investigating how the resonant optical excitation of a single quantum dot affects the motion of the oscillator. The first possibility is to set the wire in motion by exciting a quantum dot, realizing a nano-engine powered by a single quantum dot3. A second possibility is to measure non-destructively the quantum dot population via a mechanical read out.

The experiment consists in a microphotoluminescence set-up operating at a temperature of T=4K, and equipped with nanomechanical detection schemes.

References 1 I. Yeo, et al, Nature Nanotechnology 9, 106 (2014) 2 P.L. de Assis et al, Phys. Rev. Lett. 118, 117401 (2017) 3 A. Auffèves et M. Richard, Phys. Rev. A 90, 023818 (2014), Possible collaboration and networking : J. Claudon, J.M. Gérard, CEA/INAC Grenoble; A. Auffèves, O. Arcizet, Institut Néel; P.L. de Assis, Campinas, Brazil. Possible extension to a PhD: Yes Required skills: This experimental internship will deal with nano optics, nanomechanics and semi-conductor physics. Starting date: between January and April 2018 Contact: Name: Jean-Philippe Poizat Institut Néel - CNRS Phone: 04 56 38 71 65 e-mail: [email protected] information: http://neel.cnrs.fr/spip.php?rubrique47

Fig. a) Scanning electronic microscope image of the photonic “trumpet”. b)-c) Principle of the strain-mediated coupling.



41

Quantum randomness: Energetic and entropic features

Figure: The scenery of thermodynamics a) Classical thermodynamics. In heat engines, energy is extracted from thermal fluctuations induced by a hot source (dice kb) b) Quantum thermodynamics. In quantum engines, energy is extracted from quantum fluctuations induced by quantum measurement (dice hbar). Reciprocally, this framework allows deriving the energetic cost of quantum tasks performed under decoherence. General Scope: Thermodynamics is the art of randomness. It was originally developed to optimize heat engines, in other words, to efficiently turn the random thermal fluctuations experienced by hot gases into useful energy. On the other hand, quantum physics deals with systems whose states are so fragile that they can randomly fluctuate in the absence of any hot source, just because they are looked at, and measured. Such "quantum fluctuations" are usually seen as detritic. In particular, they can severely perturb the performances of the future quantum processors. However, as they alter the state of the system, quantum fluctuations can also provide energy and become a resource (Elouard et al, PRL 118, 260603 (2017); Elouard et al, npj QI 10.1038 (2017)). Research topic: We aim to transpose the tools of thermodynamics to the genuinely quantum situation where randomness is of quantum origin and induced by measurement. The candidate will contribute to design and optimize new kinds of engines extracting energy from quantum fluctuations in various experimental platforms (circuit QED, cavity QED, quantum photonics, optomechanics). On the practical side, she/he will set up tools to compute the power consumption of quantum processors. On the fundamental side, this research line sheds new light on the origin of randomness and irreversibility in the quantum regime. Possible collaboration and networking: The candidate will be part of the network Quantum Engineering Grenoble https://quantum.univ-grenoble-alpes.fr/. She/he will collaborate with top level experimental groups, as well as with theoretical partners in CQT-Singapore and the Federal University of Rio de Janeiro. Possible extension as a PhD: YESRequired skills: A good level in quantum mechanics, quantum optics and computational tools is required. Starting date: 2018 Contact: Name: Alexia Auffèves Institut Néel - CNRS Phone: +33 (0)4 76 88 79 27 e-mail:[email protected] More information: http://neel.cnrs.fr

Pure emitter dephasing : a resource for advanced solid-state single photon sources

Alexia Au↵eves

1, Jean-Michel Gerard

2, and Jean-Philippe Poizat

1

1CEA/CNRS/UJF Joint team ” Nanophysics and semiconductors ”,Institut Neel-CNRS,

BP 166, 25, rue des Martyrs, 38042 Grenoble Cedex 9, France and

2CEA/CNRS/UJF Joint team ” Nanophysics and semiconductors”,

CEA/INAC/SP2M, 17 rue des Martyrs, 38054 Grenoble, France

⇤

(Dated: September 21, 2015)

PACS numbers: 42.50.Ct; 42.50.Gy; 42.50.Pq ; 42.65.Hw

~ (1)

R (2)

U(t) = Trq[⇢q(t)Hq(t)] (3)

q = Trq[⇢q(t)Hq(t)] (4)

w = Trq[⇢q(t) ˙Hq(t)] (5)

Pe(t) = Trq

⇢q(t)

✓�z + 1

2

◆�(6)

Hq(t) = Trm[⇢m(t)(H0 + V )] =

h(⌫0 + �(t))

2

[�z + 1] (7)

�(t) = Trm[⇢m(t)gm(b + b†)] (8)

Hm(t) = Trq[⇢q(t)(Hm + V )] = h⌦b†b + hgmPe(t)(b + b†) (9)

Em(t) = h⌦Trm[⇢m(t)b†b] (10)

˙U =

h ˙�(t)

2

= w = � ˙Em (11)

w = � ˙Em (12)

!"#


Alexia Au↵eves



1





⇤

(Dated: November 10, 2015)


W (1)

ˆLµ (2)

� (3)

g2m/� (4)

w = Trq[⇢q(t) ˙Hq(t)] (5)

Pe(t) = Trq

⇢q(t)

✓�z + 1

2

◆�(6)

Hq(t) = Trm[⇢m(t)(H0 + V )] =

h(⌫0 + �(t))

2

[�z + 1] (7)

�(t) = Trm[⇢m(t)gm(b + b†)] (8)


Em(t) = h⌦Trm[⇢m(t)b†b] (10)

˙U =

h ˙�(t)

2

= w = � ˙Em (11)

w = � ˙Em (12)


Alexia Au↵eves



1





⇤



Q (1)

ˆLµ (2)

� (3)

g2m/� (4)

w = Trq[⇢q(t) ˙Hq(t)] (5)

Pe(t) = Trq

⇢q(t)

✓�z + 1

2

◆�(6)

Hq(t) = Trm[⇢m(t)(H0 + V )] =

h(⌫0 + �(t))

2

[�z + 1] (7)

�(t) = Trm[⇢m(t)gm(b + b†)] (8)


Em(t) = h⌦Trm[⇢m(t)b†b] (10)

˙U =

h ˙�(t)

2

= w = � ˙Em (11)

w = � ˙Em (12)


Alexia Au↵eves



1





⇤



~ (1)

L[⇢s] (2)

kb (3)

g2m/� (4)

w = Trq[⇢q(t) ˙Hq(t)] (5)

Pe(t) = Trq

⇢q(t)

✓�z + 1

2

◆�(6)

Hq(t) = Trm[⇢m(t)(H0 + V )] =

h(⌫0 + �(t))

2

[�z + 1] (7)

�(t) = Trm[⇢m(t)gm(b + b†)] (8)


Em(t) = h⌦Trm[⇢m(t)b†b] (10)

˙U =

h ˙�(t)

2

= w = � ˙Em (11)

w = � ˙Em (12)


Alexia Au↵eves



1





⇤



~ (1)

L[⇢s] (2)

kb (3)

g2m/� (4)

w = Trq[⇢q(t) ˙Hq(t)] (5)

Pe(t) = Trq

⇢q(t)

✓�z + 1

2

◆�(6)

Hq(t) = Trm[⇢m(t)(H0 + V )] =

h(⌫0 + �(t))

2

[�z + 1] (7)

�(t) = Trm[⇢m(t)gm(b + b†)] (8)


Em(t) = h⌦Trm[⇢m(t)b†b] (10)

˙U =

h ˙�(t)

2

= w = � ˙Em (11)

w = � ˙Em (12)


Alexia Au↵eves



1





⇤



~ (1)

L[⇢s] (2)

kb (3)

g2m/� (4)

w = Trq[⇢q(t) ˙Hq(t)] (5)

Pe(t) = Trq

⇢q(t)

✓�z + 1

2

◆�(6)

Hq(t) = Trm[⇢m(t)(H0 + V )] =

h(⌫0 + �(t))

2

[�z + 1] (7)

�(t) = Trm[⇢m(t)gm(b + b†)] (8)


Em(t) = h⌦Trm[⇢m(t)b†b] (10)

˙U =

h ˙�(t)

2

= w = � ˙Em (11)

w = � ˙Em (12)


Alexia Au↵eves



1





⇤



~ (1)

S (2)

U(t) = Trq[⇢q(t)Hq(t)] (3)

q = Trq[⇢q(t)Hq(t)] (4)

w = Trq[⇢q(t) ˙Hq(t)] (5)

Pe(t) = Trq

⇢q(t)

✓�z + 1

2

◆�(6)

Hq(t) = Trm[⇢m(t)(H0 + V )] =

h(⌫0 + �(t))

2

[�z + 1] (7)

�(t) = Trm[⇢m(t)gm(b + b†)] (8)


Em(t) = h⌦Trm[⇢m(t)b†b] (10)

˙U =

h ˙�(t)

2

= w = � ˙Em (11)

w = � ˙Em (12)


Alexia Au↵eves



1





⇤



O (1)

ˆLµ (2)

� (3)

g2m/� (4)

w = Trq[⇢q(t) ˙Hq(t)] (5)

Pe(t) = Trq

⇢q(t)

✓�z + 1

2

◆�(6)

Hq(t) = Trm[⇢m(t)(H0 + V )] =

h(⌫0 + �(t))

2

[�z + 1] (7)

�(t) = Trm[⇢m(t)gm(b + b†)] (8)


Em(t) = h⌦Trm[⇢m(t)b†b] (10)

˙U =

h ˙�(t)

2

= w = � ˙Em (11)

w = � ˙Em (12)

R

!"#W Q

kb

kbb

kkbb

W

O

S Q!"#


Alexia Au↵eves



1





⇤



O (1)

ˆLµ (2)

� (3)

g2m/� (4)

w = Trq[⇢q(t) ˙Hq(t)] (5)

Pe(t) = Trq

⇢q(t)

✓�z + 1

2

◆�(6)

Hq(t) = Trm[⇢m(t)(H0 + V )] =

h(⌫0 + �(t))

2

[�z + 1] (7)

�(t) = Trm[⇢m(t)gm(b + b†)] (8)


Em(t) = h⌦Trm[⇢m(t)b†b] (10)

˙U =

h ˙�(t)

2

= w = � ˙Em (11)

w = � ˙Em (12)

P

u

r

e

e

m

i

t

t

e

r

d

e

p

h

a

s

i

n

g

:

a

r

e

s

o

u

r

c

e

f

o

r

a

d

v

a

n

c

e

d

s

o

l

i

d

-

s

t

a

t

e

s

i

n

g

l

e

p

h

o

t

o

n

s

o

u

r

c

e

s

A

l

e

x

i

a

A

u

↵

`

e

v

e

s

1 ,

J

e

a

n

-

M

i

c

h

e

l

G

´

e

r

a

r

d

2 ,

a

n

d

J

e

a

n

-

P

h

i

l

i

p

p

e

P

o

i

z

a

t

1

1 C

E

A

/

C

N

R

S

/

U

J

F

J

o

i

n

t

t

e

a

m

”

N

a

n

o

p

h

y

s

i

c

s

a

n

d

s

e

m

i

c

o

n

d

u

c

t

o

r

s

”

,

I

n

s

t

i

t

u

t

N

´

e

e

l

-

C

N

R

S

,

B

P

1

6

6

,

2

5

,

r

u

e

d

e

s

M

a

r

t

y

r

s

,

3

8

0

4

2

G

r

e

n

o

b

l

e

C

e

d

e

x

9

,

F

r

a

n

c

e

a

n

d

2 C

E

A

/

C

N

R

S

/

U

J

F

J

o

i

n

t

t

e

a

m

”

N

a

n

o

p

h

y

s

i

c

s

a

n

d

s

e

m

i

c

o

n

d

u

c

t

o

r

s

”

,

C

E

A

/

I

N

A

C

/

S

P

2

M

,

1

7

r

u

e

d

e

s

M

a

r

t

y

r

s

,

3

8

0

5

4

G

r

e

n

o

b

l

e

,

F

r

a

n

c

e

⇤

(

D

a

t

e

d

:

N

o

v

e

m

b

e

r

1

0

,

2

0

1

5

)

PACS

num

ber

s:42

.50.

Ct;

42.5

0.G

y;42

.50.

Pq

;42

.65.

Hw

Q

(

1

)

Hs(

t)

(

2

)

�

(

3

)

g2 m/�

(

4

)

w=

T

r

q[

⇢ q(

t)˙Hq(

t)]

(

5

)

P e(

t)=

T

r

q

⇢ q(

t)✓ � z

+

1

2

◆�

(

6

)

Hq(

t)=

T

r

m[

⇢ m(

t)(

H0+

V)

]

=

h(⌫ 0

+

�(t))

2

[

� z+

1

]

(

7

)

�(t)

=

T

r

m[

⇢ m(

t)g m

(

b+

b† )

]

(

8

)

Hm

(

t)=

T

r

q[

⇢ q(

t)(

Hm

+

V)

]

=

h⌦b† b

+

hgm

P e(

t)(

b+

b† )

(

9

)

Em

(

t)=

h⌦T

r

m[

⇢ m(

t)b† b]

(

1

0

)

˙U=

h˙�(t)

2

=

w=

�˙Em

(

1

1

)

w=

�˙Em

(

1

2

)


Alexia Au↵eves



1





⇤



~ (1)

L[⇢s] (2)

kb (3)

g2m/� (4)

w = Trq[⇢q(t) ˙Hq(t)] (5)

Pe(t) = Trq

⇢q(t)

✓�z + 1

2

◆�(6)

Hq(t) = Trm[⇢m(t)(H0 + V )] =

h(⌫0 + �(t))

2

[�z + 1] (7)

�(t) = Trm[⇢m(t)gm(b + b†)] (8)


Em(t) = h⌦Trm[⇢m(t)b†b] (10)

˙U =

h ˙�(t)

2

= w = � ˙Em (11)

w = � ˙Em (12)


Alexia Au↵eves



1





⇤



~ (1)

L[⇢s] (2)

kb (3)

g2m/� (4)

w = Trq[⇢q(t) ˙Hq(t)] (5)

Pe(t) = Trq

⇢q(t)

✓�z + 1

2

◆�(6)

Hq(t) = Trm[⇢m(t)(H0 + V )] =

h(⌫0 + �(t))

2

[�z + 1] (7)

�(t) = Trm[⇢m(t)gm(b + b†)] (8)


Em(t) = h⌦Trm[⇢m(t)b†b] (10)

˙U =

h ˙�(t)

2

= w = � ˙Em (11)

w = � ˙Em (12)


Alexia Au↵eves



1





⇤



~ (1)

L[⇢s] (2)

kb (3)

g2m/� (4)

w = Trq[⇢q(t) ˙Hq(t)] (5)

Pe(t) = Trq

⇢q(t)

✓�z + 1

2

◆�(6)

Hq(t) = Trm[⇢m(t)(H0 + V )] =

h(⌫0 + �(t))

2

[�z + 1] (7)

�(t) = Trm[⇢m(t)gm(b + b†)] (8)


Em(t) = h⌦Trm[⇢m(t)b†b] (10)

˙U =

h ˙�(t)

2

= w = � ˙Em (11)

w = � ˙Em (12)


Alexia Au↵eves



1





⇤



~ (1)

S (2)

U(t) = Trq[⇢q(t)Hq(t)] (3)

q = Trq[⇢q(t)Hq(t)] (4)

w = Trq[⇢q(t) ˙Hq(t)] (5)

Pe(t) = Trq

⇢q(t)

✓�z + 1

2

◆�(6)

Hq(t) = Trm[⇢m(t)(H0 + V )] =

h(⌫0 + �(t))

2

[�z + 1] (7)

�(t) = Trm[⇢m(t)gm(b + b†)] (8)


Em(t) = h⌦Trm[⇢m(t)b†b] (10)

˙U =

h ˙�(t)

2

= w = � ˙Em (11)

w = � ˙Em (12)

!"#

O

Hs

Hs

H(

t)

(

2

)

~~ ~~~~~~~S


Alexia Au↵eves



1





⇤

(Dated: January 18, 2016)


BJ(✓) (1)

M (2)

⇤Electronic address: [email protected]



42

Bio-Activation of Mesoporous Silica Nanoparticles by selective DNA destructuration

Summary : This project aims at synthesizing mesoporous silica nanoparticles (MSNs) containing hosts in the pores and gated using DNA fragments. The cleavage of the DNA fragments by enzymes will allow the opening of the pores, thus the release in solution of the cargo. This will be applied for the detection of DNA-repairing enzymes. Detailed subject: Mesoporous silica nanoparticles (MSNs) constitute a family of nanoparticles (ca 100 nm in diameter) that is widely used for drug delivery owing to the rigidity of the matrix, the high porosity and the possible chemical modification of the surface. Interestingly, the pores (ca 2-3 nm in diameter) can be blocked when nanovalves are grafted, which destroy when a specific stimulus is applied. This has been exemplified with DNA fragments [1]. In this project, we wish to use the same principle for sensing DNA-repairing enzymes [2]. MSNs will be gated with DNA fragments containing lesions. When the repairing enzyme specific to the lesion is present, the pore-gating DNA will be cleaved and the contents of the pores will be expelled, leading to a measurable signal.

This project gathers the expertise of Didier Gasparutto (CEA/INAC/SyMMES) in the synthesis of DNA architectures, and of Xavier Cattoën (Inst Néel) in the synthesis and functionalization of mesoporous silica nanoparticles. [3] [1] Schlossbauer, et al, Angew. Chem. Int. Ed. 2010, 49, 4734 [2] G. Gines, C. Saint-Pierre, D. Gasparutto ; Biosensors & Bioelectronics (2014) 58, 81-84 [3] A. Noureddine, X. Cattoën, M. Wong Chi Man, Nanoscale 2015, 7, 11444–11452 Collaboration: Strong collaboration with Didier Gasparutto (CEA/INAC/SyMMES). This internship may be followed by a PhD thesis. Formation / Compétences : The student should have expertise in chemical synthesis and materials characterization, and a basic knowledge in biochemistry. Période envisagée pour le début du stage : 02/2017 Contact : Cattoën Xavier Institut Néel - CNRS : 04-76-88-10-42 [email protected] Plus d'informations sur : http://neel.cnrs.fr



43

Magnetic fragmentation in the Nd-based pyrochlore compounds General Scope: Geometric frustration arises in magnetic systems from the impossibility to minimize simultaneously all pair-wise exchange interactions (see the cartoon of Fig. 1). This results in the lack of conventional long range order and the stabilization of novel states of matter. Among those states, the “spin ice” state has attracted much attention over the last decades. It can be stabilized on the pyrochlore lattice (see Fig. 2), where the spins reside at the vertices of corner-sharing tetrahedra. The spin ice state is a correlated but disordered phase, characterized by a massive degeneracy. The magnetic degenerate configurations obey a local rule in each tetrahedron, the “ice-rule”, with 2 spins pointing towards the centers and 2 spins pointing outwards. Recently, a new phenomenon, called “magnetic fragmentation”, was discovered in these systems: provided certain conditions are satisfied, the magnetic moment fragments into an antiferromagnetic ordered part and a persistently fluctuating one, exhibiting correlations typical of the spin-ice. We have shown that this occurs in the Nd based material Nd2Zr2O7. The antiferromagnetic ordering arises below TN = 285 mK, and coexists with the ice-like correlations shown in Fig. 3.

Research topic and facilities available: The objective of this internship is to probe the robustness of the fragmented state by doping the system, replacing the Nd ion with the non-magnetic rare earth Y. The magnetic properties will be measured down to very low temperature (70 mK), using SQUID magnetometers equipped with dilution refrigerators developed at the Institut Néel. The student will gain knowledge in all the aspects of the experimental set-up, including cryogenic techniques and electronics. Neutron scattering measurements in Saclay will then be performed. This will allow us to determine the magnetic ground state stabilized at very low temperature in these systems. Possible collaboration and networking: collaboration with Sylvain Petit (LLB Saclay) Possible extension as a PhD: yes Required skills: Master 2 Physique Starting date: January 2018 Contact: Name: Elsa LHOTEL Institut Néel - CNRS Phone: 04.76.88.12.63 e-mail: [email protected] More information: http://neel.cnrs.fr/spip.php?rubrique11

Fig. 3: Ice-like pattern observed by inelastic neutron scattering at E=50µeV, at T=60mK. The red spots denote the Bragg peaks typical of the antiferromagnetic ordering.

Fig. 2: Pyrochlore

lattice

Fig. 1: Ising spins in antiferromagnetic

interactions in a triangle: the “?” illustrates that different degenerate

configurations are possible.

!"#!"#

!"#



44

Chemical mapping at the sub-nm scale of ultraviolet µ-LEDs

Cartographie chimique à l’échelle sub-nanométrique de dispositifs µ-LEDS pour UV

Context: The extension of the Light Emitted Diode (LED) technology towards the ultraviolet (UV) wavelength range is considered as a research priority to replace the use of highly-toxic mercury lamps in the domain of disinfection. Moreover, the development of an eco-friendly mercury-free UV technology would also open up a number of applications in the domains of health, agriculture, food production, and environment preservation. In this context, LEDs based on Aluminium Gallium Nitrides (AlGaN) semiconductors appear very promising candidates.

Objectives: The target of this study is the analysis of AlGaN layers and nanostructures (quantum wells and quantum dots) grown by Plasma Assisted Molecular Beam Epitaxy (PA-MBE), to correlate their optical performance with their structural arrangement and three-dimensional (3D) chemical composition at the nanometer scale. It is carried out in the framework of a close collaboration between two groups of complementary expertises: CEA-INAC/CNRS-Institut Néel joint team “Nanophysics and Semiconductors” (NPSC) (Eva Monroy and Catherine Bougerol) and CEA-LETI group of the Nano-Characterization Platform (PFNC) (Adeline Grenier). The precise tasks of the student will be the following: − He/she will be in charge of the optical characterization of the structures by photoluminescence

performed at NPSC facilities under the supervision of Eva Monroy. − He/she will analyse the samples by atom probe tomography (APT) for 3D nanoscale mapping of

alloy homogeneity and doping at PFNC facilities, under the supervision of Adeline Grenier. − He/she will work on the interpretation of the results by correlation of experimental studies with

theoretical calculations. − Besides these main tasks, he/she will also participate in the growth of a series of structures by

MBE, and in their structural characterization by transmission electron microscopy (TEM) under the supervision of Eva Monroy and Catherine Bougerol.

The host laboratories have extensive experience in the growth and characterization of AlGaN-based planar layers and nanostructures (quantum wells, quantum dots, nanowires). The protocol for APT characterization of such structures has also been validated a current PhD student.

− 5nm

Example of the 3D APT reconstruction of a Mg-doped GaN layer evidencing the nm scale clustering of Mg atoms (Mg atoms yellow/light grey, Ga atoms blue/dark grey) Possible extension as a PhD: The extension would take place in the framework of a collaboration with LETI-DOPT towards the development of UV LED. Required skills: This study requires high motivation for experimental research in the field of semiconductor devices and nanostructures. Starting date: Spring 2018 Contact: Catherine BOUGEROL, Institut Néel – CNRS, [email protected] More information: http://neel.cnrs.


45

Charge transport in organic semiconductors: atomistic investigation of dynamic disorder

General Scope : The multidisciplinary field of organic electronics proposes a new generation of lightweight, flexible and sustainable devices (e.g. transistors, light emitting diodes or solar cells) based on pi-conjugated molecules as active elements. The subject of the proposed internship is to use the most recent fundamental advances in the field to study charge transport in organic semiconductors, a phenomenon that is transversal to all domains of applications. Research topic and facilities available: The fundamental question of how electrons move in organic crystals has remained unanswered for several decades. Only in recent times the community started to acknowledge the central role of molecular thermal motion in these solids, that are kept together by non-covalent interactions : this so-called “dynamic disorder” confers to transport an original character that is general to the whole class of organic materials. Many aspects of the emerging microscopic theory are still to be explored. Key current challenges consist in the achievement of a quantitative agreement with experiments and in suggesting design principles for improving the performances. To this aim, the candidate will investigate the impact of dynamic disorder in realistic molecular systems by means of complementary atomistic computational techniques, including classical molecular dynamics, DFT electronic structure calculations and electrostatic models. Possible specific themes concern the assessment of the contribution to the dynamic disorder of intermolecular electrostatic interactions or of semiconductor-dielectic interfaces. The candidate will receive appropriate training for each task and will use computational ressources available at Institut Néel.

Figure: Left: a realistic model of the organic semiconductor pentacene on a SiOx dielectric substrate. Right: skecth of a hole wavepacket propagating under the effect of thermal dynamic fluctuations in a one-dimensional array of molecules. Scholarships: Foreign candidates may apply for financial support from IDEX-Uni. Grenoble Alpes. Possible collaboration and networking: Collaborations with groups in Europe and US are possible. Possible extension as a PhD: A follow-up PhD is welcomed (possible support from Ecole Doctorale, Lanef and Fondation Nanosciences PhD programs). Required skills: Strong motivation and interest for condensed matter physics and computational materials science. Basic knowledge of scientific computing and coding. Starting date: As soon as possible Contact: Gabriele D'Avino, Simone Fratini, Institut Néel - CNRS e-mail: [email protected] [email protected]


46

Nonlinear optics with hybrid plasmonic nanostructures General Scope: The race for ever more optimized electronic components is reaching its limits nowadays, in terms of computation speed, efficiency and miniaturization. In this context, alternatives to electronic-based technology are being investigated more and more actively, with important investments put in photonics and quantum information. With its collective, coherent and localized states coupling photons and electrons, plasmonics appears to be an interesting path for coherent data computing (transistor) or coupling (multiplexing) with nanometric sized components. Other fascinating elements are nonlinear optical materials (KTP, BBO...), whose optical properties (wave mixing, Kerr effect, nonlinear absorption, phase self-modulation...) make them ideal materials for nonlinear operations like the ones used for data operations. However, their miniaturization leads to a strong efficiency drop, thus needing optical cavities to circumvent the issue. Combining plasmonics nanostructures and nano-sized nonlinear crystals hence seems like a promising compact and efficient solution for this kind of applications. Research topic and facilities available: The objective of this internship is to explore the coupling between a nano-sized nonlinear crystal and a plasmonic (gold or aluminum) nano-antenna in a single hybrid nanostructure. The main work will be to investigate the effect of plasmonic resonances on the second harmonic or sum-frequency generation, two nonlinear processes where two photons (from a single or two laser beams) are converted into a single one. For this proposal, we will fabricate a set of individually designed hybrid structures using clean room techniques, before studying them by using an existing setup that has already demonstrated excellent specifications with nanometer-scale control of the nanostructure position, thanks to a particle tracking algorithm, and single photon sensitivity with ultra low-noise detectors. This project will be part of a wider research program, led by G. Bachelier, that has been granted by the ANR. Hence, all the necessary means will be available. Collaborations and networking: N. Chauvet, M. Ethis de Corny and G. Laurent (PhD, NOF), G. Nogues (NPSC), G. Dantelle (OPTIMA). Possible extension as a PhD: yes. Required skills: An experimentalist profile is targeted here. Though, a theoretical background in electromagnetism, nonlinear optics and/or programming skills in Matlab/Comsol will be welcome. Starting date: As soon as possible Contact: Guillaume Bachelier Institut Néel - CNRS Phone: +334 56 38 71 46 e-mail: [email protected]

Nicolas Chauvet Institut Néel - CNRS Phone: +334 76 88 70 61 e-mail: [email protected]

More information: http://neel.cnrs.fr

200 nm


47

Photon pair generation in hybrid nonlinear/plasmonic nanostructures

General Scope: Nonlinear nanophotonics is a great opportunity for opening new and promising paths toward a wide range of practical applications in sensors, quantum computers, cryptography devices... The main challenge is to enhance non-linear response of nanosized particles in order to integrate them in optical components. We have a particular interest in Spontaneous Parametric Down Conversion (SPDC) where a photon is split in two photons of smaller energy. We use metallic structures supporting localised surface plasmons (LSPs), i.e. collective oscillations of free electrons: when excited with a laser tuned at the LSP resonance wavelength, these structures exhibit a great near field enhancement that strongly amplifies nonlinear processes. Research topic and facilities available: The main objective is to achieve nanosize photons pair sources. Our team has developed an approach mixing analytical and numerical simulations to quantitatively model photon pair generation in composite structures made of plasmonic antennas coupled to a non linear crystal. The candidate will learn Finite Element Methods (with COMSOL Multiphysics) to model linear and non linear responses (photon pair generation, second harmonic generation) under realistic experimental configurations. He will investigate the relation between particle geometry and the SPDC rate. A later stage of the project is to perform Bell’s inequality test simulations to study photon entanglement at the nanoscale. This project is supported by an ANR grant (TWo photons generation In plasmonic Nanoantennas). Hence, all necessary means will be available. Possible collaboration and networking: A. Drezet (NOF), N. Chauvet and G. Laurent (PhD, NOF), G. Nogues (NPSC), G. Dantelle and B. Boulanger (Optima). Possible extension as a PhD: Yes Required skills: A theoretician profile is targeted. Nonlinear optics and/or programming skills in MATLAB/COMSOL will be welcome. Starting date: As soon as possible. Contact: Guillaume Bachelier Institut Néel - CNRS Phone: +334 56 38 71 46 e-mail: [email protected]

Guillaume Laurent Institut Néel - CNRS Phone: +334 76 88 74 72 e-mail: [email protected]

More information: http://neel.cnrs.fr

Figure 1: Left: SEM image of a 80nm KTP standing between two aluminum antennas. Right: scattered near field at the fundamental frequency computed by a finite element method.


48

Graphene based superconducting quantum bit General Scope: The future of nanoelectronics will be quantum. The downscaling in electronics has now reached a point where the size of the devices (less than 10 nm) means that their quantum behavior must be taken into account. While this might be seen by some industries as a major problem this also gives a real opportunity to imagine and build devices with new quantum functionalities. A key building block for future quantum electronics systems is the quantum bit. Such system has two possible states (0 and 1) that follow the laws of quantum mechanics. One example is that one might build any superposition of 0 and 1. This will have implications for building future quantum computers. Research topic and facilities available: In this work we want to build a new type of device to implement a quantum bit that would have strong advantages over other competing systems. The idea is to use the know-how that has been developed in the superconducting quantum bit community over the past 20 years and integrate in the core of the system a semiconducting material to bring novel electrical functionality to the device, in the form of a voltage-tunable energy. We will use graphene, a two-dimensional zero-band-gap semiconductor, because of the potential scalability of such approach. Such device is expected to behave as a quantum two-level system with an energy structure that can be tuned with an electric field (gate) thanks to graphene (see figure). A one atom-thick sheet of graphene will thus have to be integrated into a superconducting quantum bit design using nanofabrication techniques available at the Institute. Such sample will then be measured at very low temperature (20mK) in a dilution refrigerator using radiofrequency (1-10 GHz) techniques, which is already operating. After the demonstration of the electrical tunability, more advanced measurements will be carried out in the following PhD project: lifetime, coherence ,coherent manipulation...

Figure 2: Optical image of the first generation of graphene based superconducting qubit. The graphene link (Josephson junction), 200nm long, is not visible at this scale. On the right, the equivalent electrical circuit shows that this device will behave as an electrically tunable quantum two-level system. Possible collaboration and networking: The student will be part of the Hybrid team, which has a multidisciplinary expertise (growth, nanofabrication, electronic transport, spectroscopy...). The team has also several external collaborations worldwide (France, Germany, Canada). Possible extension as a PhD: Yes Required skills: The internship (and the PhD thesis) will require a solid background in solid state/condensed matter physics. The work will be mainly experimental. The candidate is expected to be strongly motivated to learn the associated techniques (nanofabrication in clean room, radiofrequency electronics, cryogenics...) and engage in an hands-on experimental work. Starting date: March 2018 Contact: Name: Julien Renard, Institut Néel - CNRS Phone: 0456387176 e-mail:[email protected] More information: http://neel.cnrs.fr


49

Theory of topological properties in microwave-irradiated Josephson junctions

General Scope: Josephson junctions usually connect two superconducting terminals by a weak link. Recently, junctions with three terminals (3TJ) have revealed a great potential in terms of multiple Cooper pair modes (quartets) and topological properties. Microwave irradiation with chirality is proposed as a versatile tool to induce such topological properties. In a 3TJ made of a quantum dot (with one or a few levels), topological transitions manifest in the low-energy behavior of the Andreev states that form within the junction. For a single-level dot, such a description is indeed equivalent to the physics of electrons in a generalized graphene lattice Research topic and facilities available: i) The topic of the internship is to investigate electronic transport probes of topological properties. Indeed, Berry phase and Berry curvature of the Andreev state wavefunctions can be accessed through transport measurements, applying suitable voltages. The interplay between this « topological current » and multiple Cooper pair transport will be studied. ii) The mapping between a 3TJ and graphene holds in the limit of an infinite superconducting gap. The superconducting wavefunction, depending on two phases, is mapped onto that of electrons on an honeycomb lattice, depending on two wavevectors. This description has to be modified to incorporate the superconductor quasiparticles at finite energy. Possible collaboration and networking: An ongoing collaboration exists with Instituto Balseiro (Argentina) on this topic. Possible extension as a PhD: The internship is opened on a PhD project. The general topic will be at the interface between superconducting Josephson junctions and cold atom condensates that can also form junctions and multijunctions. In a mapping of the latter on an equivalent graphene-like lattice, one can induce topological properties and probe them on edge states, that are more difficult to achieve in the superconducting equivalent. This project is developed in collaboration with LPMMC, Grenoble. Required skills: A good ability in quantum mechanics and training in superconductivity are required. Starting date: March 2018 Contact: Denis FEINBERG Institut Néel - CNRS Phone: 04 76 88 74 56 e-mail: [email protected] More information: http://neel.cnrs.fr


50

Quantum Hall interferometry in high mobility Graphene Graphene is a 2D material that has attracted a huge interest since its discovery in 2005. Its gapless linear band structure that mimics massless Dirac fermions has led to the discovery of a wealth of new exciting transport properties. Moreover, the possibility to engineer very high mobility graphene devices in which electrons can travel in a ballistic fashion makes graphene the perfect playground to investigate new quantum coherent phenomena and interaction effects in the integer and fractional quantum Hall regimes.

The goal of the internship is to study an electronic analogue of the optical Fabry-Pérot interferometer in the quantum Hall regime of graphene. In the quantum Hall effect, electron transport is confined in one-dimensional channels that propagate along the edges of the sample. The use of electrostatic gate electrodes enables the control of their path to modify the interference pattern, and also the realization of constrictions (quantum point contacts [1]) that act as semi-reflecting mirrors for electron wave packets. These two basics elements are the keys to engineer quantum Hall interferometers (see figures). During the internship, the student will learn the van-der Waals pick-up technique used to make high mobility graphene devices and carry out measurements on state-of-the-art devices to unveil quantum interferences. To enter the quantum Hall regime and study the physics of quantum Hall interferometers, low-noise quantum transport measurements will be performed at very low temperature (~10mK, dilution fridge) and high magnetic field (18T). The student will be involved at all levels, from the device fabrication process, to the transport measurements at very low temperature and high magnetic field, to the data analysis and interpretation. For the PhD perspective, efforts will be focused on two important objectives, namely investigating the nature of the fractional quantum Hall effect with interferometers, and the interplay between the quantum Hall effect and superconductivity. [1] K. Zimmermann et al, Gate-tunable transmission of quantum Hall edge channels in graphene quantum point contacts. Nature Communications 8:14983 (2017) Ce stage pourra se poursuivre par une thèse : Yes (PhD grant funded by a european project) Formation / Compétences : We look for highly motivated students with a strong background in condensed matter physics / quantum physics, and which are willing to address fundamental questions of advanced quantum solid-states physics. Période envisagée pour le début du stage : early 2018 Contact : Benjamin Sacépé Institut Néel – CNRS Quantum Nano-Electronics and Spectroscopy (QNES) team email: [email protected]; website: http://sacepe-quest.neel.cnrs.fr/ Tel: 0476881079


51

Dielectric properties of the Cooper-pair insulator

When a superconducting disordered thin film is subjected to an increase of disorder or to a strong magnetic field (B) it can undergo a transition to an insulating state. This transition is a quantum phase transition (driven by a change of a parameter of the Hamiltonian at T=0) between two antinomic ground states, the superconducting and insulating ground states. In recent years the insulator drew significant interest due to the body of experimental work that indicates that charge carriers in it are localized Cooper-pairs [1]. It is thus considered as a unique playground to investigate an interacting, many-body quantum system of localized Cooper-pairs in a disordered potential.

The transition to the so-called Cooper-pair insulator is easily tuned in experiments by applying a strong perpendicular magnetic field. The above figure shows a typical B-tuned transition from superconductor at B=0 to the Cooper-pair insulator at finite B with a diverging magnetoresistance resistance peak at the lowest temperature. The nature of the insulator in this magnetoresistance peak is the focus of our current research activities.

The goal of this Master project is to perform innovative high frequency measurements of the dielectric properties of the Cooper-pair insulator using state-of-the-art superconducting micro-wave resonators. The underlying physics to unveil is a possible signature of a new transition to a new insulating state with strictly zero conductivity at finite temperature (called many-body localized state) [2]. The student will participate in the design of RF superconducting resonators that serve to probe of the dielectric constant. She/He will prepare and characterize superconducting samples by magneto-transport measurements (down to 10mK and 18T), and start the first high frequency measurements of the dielectric constant. These initial measurements will give crucial information about the role of Coulomb interaction in the superconductor insulator transition.

[1] B. Sacépé et al. Localization of preformed Cooper pairs in disordered superconductors, Nature Physics 7, 132 (2011). http://arxiv.org/abs/1012.3630 [2] M. Ovadia et al. Evidence for a Finite Temperature Insulator. Nature Scientific Reports 5:13503 (2015) http://www.nature.com/articles/srep13503 Interactions et collaborations éventuelles : Superconducting resonators : Alessandro Monfardini, HELFA team. Landau Institute for Theoretical Physics (Moscow). Stuttgart University Ce stage pourra se poursuivre par une thèse : Yes Formation / Compétences : We look for highly motivated students with a strong background in condensed matter physics / quantum physics, and which are willing address fundamental questions of advanced solid-states physics. Période envisagée pour le début du stage : early 2018 Contact : Benjamin Sacépé Institut Néel – CNRS Quantum Nano-Electronics and Spectroscopy (QNES) team) email: [email protected]; website: http://sacepe-quest.neel.cnrs.fr/ Tel: 04 76 88 10 79


52

Dynamics of many-body systems in quantum electronics General Scope: Real time manipulation of simple quantum objects in electrical circuits has now become a routine task in the lab. The present frontier of research now aims at mastering driven many-body quantum systems, which asks for novel theoretical ideas. Our team has developed powerful many-body wave-functions techniques based on time-dependent many-body Schrödinger cats, that can tackle systems with exponentially large Hilbert space. Quantitative modeling of experiments involving complex architectures and large number of quantum degrees of freedom is becoming within reach. Research topic and facilities available: The internship will aim to compute equilibrium correlation functions of quantum open systems using the non-equilibrium techniques mentioned above. The model will be relevant to describe a superconducting qubit coupled to a transmission line, see Illustration below, with the goal of computing the many-body scattering matrix of photons impinging on the qubit. The numerical simulations will be performed on the 256 cores cluster at NEEL.

Possible collaboration and networking: The theoretical developments have been made through a network of collaborators at the Cavendish Lab, University of Manchester, University of Witwatersrand, and IIT Bombay, and in collaboration with the experimental team of Nicolas Roch at NEEL. Joint grants could allow the student to spend some of his research time abroad during his PhD. Possible extension as a PhD: Yes Required skills: Besides general knowledge in quantum mechanics, basics in superconductivity, solid state physics, and many-body methodology would be an asset. The student will be involved with both analytical and numerical calculations, and welcome to write his own code as part of his training. Starting date: The internship can start anytime during the academic year 2017/ 2018, but should last a minimum of 2 months (one-year Diplomarbeit is possible), with a base salary of 546 euros/month. Contact: Name: Serge Florens Institut Néel - CNRS Phone: +33-4-76-88-74-54 e-mail: [email protected]

Illustration 1: Experimental platform for many-body quantum optics. Superconducting qubit (left zoom) coupled to a transmission line made from 5000 resonators in series (few are shown in the right zoom).


53

Novel quantum interference experiments with ultra-short single electron charge pulses

General Scope: Interference experiments are at the heart of quantum mechanics and have lead to immense achievements over the last two decades, in particular in the field of quantum optics. Due to the tremendous progress in nanofabrication techniques, it is now possible to isolate and manipulate coherently single electrons, which opens the way to perform quantum optics like experiments with electrons [Hermelin et al., Nature 2011; Dubois et al., Nature 2013].At the same time nanoelectronics experiments are shifting towards frequencies in the GHz range and beyond. These frequencies are now becoming comparable to the internal characteristic time scales that set the quantum dynamics of the devices, resulting in new opportunities for studying the dynamical aspects of quantum mechanics. Research topic and facilities available: The aim of the proposed PhD subject is to develop unprecedented realization of quantum interference experiments (see figure) by manipulating and detecting electrons in a ballistic quantum conductor at the single electron level by using ultra-short electron wave packets. In order to generate such ultra short electron wave-packets, we will leverage on the progress made on THz photon production and use photon to electron conversion devices to engineer THz electronic charge pulses that can be used in quantum nanoelectronics. The ability to generate voltage pulses with a duration as short as one picosecond will allow to access completely new regimes of quantum physics by studying its real time dynamical effects.

Possible collaboration and networking: This project is realized in close collaboration with the nanoelectronics group in Saclay (C. Glattli), the THz laboratory of the Université de Savoie Mont-Blanc (J.F. Roux & J.L. Coutaz) and the theory group of CEA Grenoble (X. Waintal). Possible extension as a PhD: yes Required skills: The candidate should have a strong background in quantum mechanics and solid-state physics. Starting date: Spring 2018 Contact: Name: BAUERLE Christopher Institut Néel – CNRS, Grenoble Phone: 04 76 88 78 43 e-mail: [email protected] More information: http://neel.cnrs.fr


54

Quantum superpositions of causal relations General context : The study of causal relations has recently gained a lot of interest in the fields of quantum foundations and quantum information. The general objective is to investigate the possible causal relations between events that can exist in the quantum world, and see how they differ from classical relations.

For instance, just like quantum objects can be in a superposition of two incompatible states, one may wonder if there can be superpositions of causal relations: e.g., for the case of 2 events A and B, a situation of the kind “|A causes B> + |B causes A>”.

A framework was recently developed [1] to analyse quantum processes that are incompatible with a definite causal order (i.e., for which one cannot say that A acts before and causes what happens at B, or vice versa). Such processes are called causally non-separable; an example is the quantum switch [2] represented on the right. The framework also allows for processes that generate some new kind of noncausal correlations, which violate so-called causal inequalities; it remains however an open question, whether such processes can indeed be realised in practice. Research project: Building upon the above quantum switch, this project aims at investigating various new practical examples of quantum processes, to test their causal nonseparability and their potential ability to violate causal inequalities. The candidate will resort in particular to the useful analogy between causal nonseparability and entanglement, and between causal inequalities and Bell inequalities [3]. Some of the examples under investigation may not be described in the current form of the framework of [1], which will lead the candidate to propose possible ways to generalize the framework. Various types of “superpositions of causal relations” will be considered, which may involve more than 2 events. [1] O. Oreshkov, F. Costa, and #. Brukner, Nat. Commun. 3, 1092 (2012). [2] G. Chiribella et al., Phys. Rev. A 88, 022318 (2013); M. Araújo et al., Phys. Rev. Lett. 113, 250402 (2014). [3] M. Araújo et al., New J. Phys. 17, 102001 (2015); C. Branciard et al., New J. Phys. 18, 013008 (2016). Interactions and possible collaborations:

This project will be supervised by Cyril Branciard, and will be conducted in collaboration with the theory group of Alexia Auffèves. The candidate will benefit from interactions with the other group members and from their expertise in a large range of domains (quantum foundations, quantum information, quantum optics, cavity and circuit QED, quantum thermodynamics…). Interactions will also be possible with the group of Prof. Nicolas Gisin at the University of Geneva (Switzerland). This project may be followed by a PhD depending on funding opportunities.Training / Skills: A good knowledge of the formalism of quantum theory and a strong interest in fundamental physics, in particular in quantum foundations and quantum information, are required. Starting date: early 2018

Contact: Branciard Cyril Institut Néel – CNRS. tel: 04 56 38 70 60; e-mail: [email protected] information on http://neel.cnrs.fr

The quantum switch: the 2 polarizing beam splitters (PBS) transmit horizontally polarised photons and reflect vertically polarised ones; a |H> photon will thus go to A and then to B, while a |V> photon will go to B and then to A. A photon in a quantum superposition |H>+|V> will thus go to A then B, and B then A, in superposition.


55

Circuit-QED: amplification at the single-photon level General Scope: During the last decade, it has been demonstrated that superconducting Josephson circuits behave as quantum bits and are very well suited to realize advanced quantum mechanical experiments. These circuits appear as artificial atoms whose properties are defined by their electronic characteristics (capacitance, inductance and tunnel barrier). Moreover, given their mesoscopic size, these quantum bits couple very strongly to electromagnetic radiations in the microwave range. Thus, it is now possible to perform quantum optics experiments using microwave photons and to unravel light-matter interactions using circuits. This field is dubbed circuit-QED (Quantum Electro-Dynamics). Measuring these microwave photons with very high quantum efficiency remains a tremendous challenge, since the energy conveyed by one single microwave photon is hundreds thousand times smaller than the one of usual optical photons. Yet signals at the single-photon level can be measured using Josephson parametric amplifiers [1]. In our team we are now using superconducting metamaterials (see figure) to engineer the next generation of parametric amplifiers [2]. These new devices allow us to explore the quantum limits of amplification as well as to perform quantum optics experiments. [1] Widely Tunable, Nondegenerate Three-Wave Mixing Microwave Device Operating near the Quantum Limit, N. Roch, et al. , Phys. Rev. Lett. 108, 147701 (2012). [2] L. Planat. , et al. , in preparation (2017). Research topic and facilities available: Our team has a strong experience in nanofabrication, microwave electronics and cryogenic equipment. First, the student will be in charge of the theoretical modeling of the superconducting parametric amplifier. She/He will then carry out the measurements of the device at very low temperature (30mK), using one of the three fully equipped dilution refrigerators of the team. The devices are fabricated in the clean room of the Neel Institute (Nanofab). If the candidate is interested in learning these fabrication techniques, she/he can be associated to this part of the project. Possible collaboration and networking: Our team is part of several national and international networks. For this specific project we are collaborating closely with Prof. K. Murch at Washington University in Saint-Louis, Missouri, USA, Prof. R. Vijay at TIFR, Mumbai, India, and Prof. I. Pop at KIT, Karlsruhe, Germany. This internship can be pursued toward a PhD Required skills: Master 2 or Engineering degree. We are seeking motivated students who want to take part to a state of the art experiment and put some efforts in the theoretical understanding of quantum effects in Josephson parametric amplifiers. Starting date: Flexible

Contact: ROCH Nicolas Institut Néel - CNRS : phone: +33 4 56 38 71 77 email: [email protected] More information : http://neel.cnrs.fr & http://perso.neel.cnrs.fr/nicolas.roch

SEM image of a metamaterial-based Josephson parametric amplifier. The metamaterial is made of 70 SQUIDs as shown in the inset. From [2]


56

Confined nucleation and growth of molecular nanocrystals for biophotonics and advanced solid-state NMR

General Scope: We develop the synthesis of new tracers, highly fluorescent, for cerebral imaging based on two-photon fluorescence scanning microscopy: injection of these tracers into the blood circulation to visualize tumour micro-vascularisation of small animals. These tracers (20-100 nm) are based on molecular nanocrystals (NCs) constituted by a high number of molecules (105-106) allowing good photostability and high cross sections of absorption and fluorescence emissions leading to bright tracers to increase fluorescence contrasts and 3D imaging depths. On the other hand, the shaping of molecular NCs in solutions allow to enhance the sensitivity (by several orders of magnitude) and the resolution of a just emerging method of magnetic resonance spectroscopy called Magic Angle Spinning - Dynamic Nuclear Polarization (MAS-DNP), developed at CEA-INAC. This MAS-DNP spectroscopy will be used for 3D structure determinations (NMR crystallography) of many solid-state systems, which do not easily form large enough crystals (>100 mm) suitable for single crystal X-ray diffraction studies and cannot be easily isotopically enriched in 13C and 15N. Thus, such developments are highly relevant, especially for supramolecular systems, drugs, natural products, self-assembled peptides/nucleotides… etc. Research topic and facilities available: The objective will be to control the confined nucleation and growth of molecular NCs in droplets of organic solvents. For that, organic compounds will be dissolved in solvents miscible with water (alcohols, THF, dioxane…). The resulting solutions will be sprayed and suddenly dispersed in water. As water is generally a non-solvent for molecular phases, the corresponding NCs will grow when the solvent droplets will be gradually mixed in water. We recently made a step-forward in the control of this process by producing nanometer-sized crystals of progesterone (around 50 nm in diameter) as shown by scanning electron microscopy in the figure below. The goal is now to produce monodisperse initial droplets to obtain then narrow size distributions of NCs (50-100 nm) by optimizing the nanocrystallization reactor and confined nucleation conditions. The resulting NCs will be characterized by X-ray diffraction, electron microscopies (SEM and TEM), dynamic light scattering, Raman and fluorescence spectroscopies. This research is part of a highly challenging ERC (European Research Council) project on developments of MAS-DNP spectroscopy. Indeed, we believe that our generic process will be widely applicable for molecules exhibiting both a large solubility in solvents miscible with water and a negligible solubility in water, which is the case of a large number of organic compounds. Finally, we will plan to couple this confined nanocrystallization method in solutions to sol-gel chemistry, in order to prepare through a one-step process core-shell nanoparticles: fluorescent NCs surrounded by an amorphous silicate crust for medical imaging applications (highly fluorescent tracers).

Nanocrystals of progesterone obtained from a methanol solution, sprayed and injected in water.

Possible collaborations and networking: INAC-CEA, CHU-Grenoble, ENS Lyon… Possible extension as a PhD: Yes Required skills: Solid-state and physical chemistry, basic knowledge on physicochemical and structural characterizations of materials. Starting date: 2017-18 Contact : Alain Ibanez, Institut Néel, CNRS. Phone: 0476887805 e-mail: [email protected] More information: http://neel.cnrs.fr


57

New generation of eco-efficient phosphors for white LED lighting. General Scope: As lighting represent around 19% of global energy consumption, the development of white LEDs (wLEDs) is a huge challenge for energy saving. Commercial wLEDs combine a blue LED chip with a luminescent powder, called phosphor. Thus, by mixing the incident blue emission of the chip with the photoluminescence (PL) of the phosphor (yellow for the typical YAG:Ce phosphor), white lighting can be obtained. Phosphor is a key constituent of wLEDs for the cost (20 % of devices), emission quality, global efficiency and thermal stability. Currently used phosphors can produce high luminous efficiencies but are constituted by expensive and strategic elements and suffer of poor color quality leading to cold white lighting and low chromatic stability. At Institut Néel, we develop a new type of phosphors based on glassy aluminum borate micropowders. These patented phosphors allow to produce intense broadband emissions in the whole visible spectrum (see figure below), from carbon-related radicals trapped in the glassy grains. This open promising perspectives to produce confortable white light for eyes with excellent color rendering. Moreover these stable phosphors are constituted of non-toxic and abundant elements (low cost) for the development of eco-efficient wLEDs. Research topic and facilities available: Based on these promissing premilinary results, the firt goal of this thesis will be to optimize the elaboration of aluminum borate powders by soft chemistry. Their syntheses and chemical compositions will be adjusted by using the molecular precursor method (modified Pechini) varying the nature and relative amounts of precursors in the initial solutions leading to the formation of resins through metal complexations and polymerization (polyesterification) of organic-inorganic networks. Then, thermal treatments of resins (temperature, heating rates, nature of controlled atmosphere), which induce the generation of luminescent centers will be accurately studied involving microcalorimetry coupled with mass spectroscopy, X-ray diffraction, electron microscopies and PL properties. Thus, we expect to enhance the PL efficiency (external quantum yields) and to adjust the width and position of the PL band in the whole visible range to obtain high color rendering (warm white lighting). We will develop also the phosphor shaping (pellets or powders dispersed in resins) to obtain phosphor coating with highly PL efficiency, optimized light extraction and good spectral emission. Another important goal will be to understand the origin and role of emitting centers, which seems to be related to trapped carbogeneous species to optimize then the PL properties by coupling complementary technics: FTIR, UV-Vis spectroscopy, X-ray diffraction and also EPR, NMR in collaboration with INAC-CEA Grenoble.

Left) Broad PL emission of the phosphor (450 and 800 nm) and residual near UV incident radiation of the LED chip (365 nm excitation). Right) First lighting prototype involving a NUV-LED and the aluminum borate powder dispersed in a silicone matrix Possible collaboration and networking: Institut de Recherche Chimie-Paris; INAC-CEA Grenoble Led Engineering Development company Possible extension as a PhD: Yes Required skills: Good skills in materials science: Solid-state and physical chemistry, physicochemical and structural characterizations of materials. Starting date: 2017-18 Contact : Alain Ibanez, Institut Néel, CNRS. Phone: 0476887805 e-mail: [email protected] More information: http://neel.cnrs.fr


58

Spin Polarisation in Graphene Functionalized with 2D MolecularAssemblies

General Scope: Graphene has been widely used to fabricate field-effect transistors and sensors, and recently considered for spintronics. For that purpose, the spin of electrons needs to be manipulated without altering the advantageous high electron mobility. This can either be encoded in graphene itself, by increasing its spin-orbit interaction, or achieved by a proximity effect. These imply to bring foreign atoms, like heavy elements, close to graphene. We are investigating the electron transport through graphene functionalised with planar molecules enclosing such atoms. The ultimate objective is to produce intriguing topological electronic phases like quantum spin Hall states. Research topic and facilities available: Graphene is a platform where a wealth of molecular building blocks can be assembled to form truly 2D lattices of spins and heavy atoms. Organic chemists provide us with specifically-designed molecules (see figure) having a close contact to graphene but with a weak bonding to preserve graphene’s unique electronic properties. A central objective of the internship is to understand the subtle yet decisive influence of the molecular networks on these properties. We will probe the extent of the spin-orbit interaction with transport measurements at varying magnetic field and down to (very) low temperatures. We will exploit devices in the shape of cross-bars (see figure), i.e. with two overlapping graphene ribbons whose individual and cross transport will be investigated. In between the ribbons the molecules will be intercalated. The host group controls the synthesis and manipulation of high quality graphene cross-bars, and has developed optical spectroscopy (Raman) tools giving insights into charge transfers at the molecule-graphene interface. The host group also has access to the Néel Institute cleanrooms where the devices will be prepared. Very-low temperature magneto transport measurements will rely on the group’s helium dilution cryostats.

Molecular monolayer addressed between graphene electrodes. a) Scheme of a molecular assembly on graphene. b-c) Principles of the electron transport measurement in a 4-probed graphene crossbar : the geometry provides several measurements configurations.

Possible collaboration and networking: This internship takes part of a national-scale project involving Néel Institute, CEA-IRAMIS, Institut des Sciences Moléculaires. Magnetotransport experiments will be performed with LPS-Orsay. Possible extension as a PhD: Yes Required skills: A Master 2 level in Condensed Matter Physics or Nanosciences is required. The student will be involved in the nanofabrication and mesoscopic transport: motivation to learn these aspects is recommended. Starting date: October 2018 Contact: Name: Vincent BOUCHIAT Institut Néel - CNRS Phone: 04 56 38 70 74 e-mail: [email protected] More information: http://neel.cnrs.fr/spip.php?rubrique754


59

Non-linear phenomena in topological phases of matter

General Scope : Topological phases of matter present a fascinating platform to probe the intersection between high-energy physics, condensed matter and the mathematical field of topology. For instance, apparently simple properties like the electrical conductivity are determined by interesting but puzzling features of quantum field theory known as quantum anomalies. These surprising connection has enabled experimentalists and theorists in the field to investigate and extend phenomena previously restricted to the realm of particle physics, and to go beyond current knowledge in material science to predict novel and useful effects. Research topic and facilities available : The successful applicant will learn a broad number of techniques — including quantum field theory methods in condensed matter and high-energy physics — that will be applied to study non-linear responses of topological phases to external perturbations such as electromagnetic fields or strain. Possible collaboration and networking : Regular collaboration with local and international groups as well as close contact with experiments is foreseen. Locally, the unique environment at Néel Institut and the CNRS campus in Grenoble is ideal to pursue collaborations and experimental input to theory. Possible extension as a PhD: A succesful M2 candidate will be encouraged to pursue a PhD studying topological matter in topics related to the proposed project. It is possible that the successful applicant will spend short periods of time at University of California at Berkeley, and/or other places.

Required skills: We seek strongly motivated applicants able to work independently as well as to cooperate and communicate with other researchers and students. Together with the relevant qualifications, the applicant must be comfortable with concepts in quantum mechanics and solid state physics. Basic knowledge of many-body theory and/or high-energy physics, is desirable. Proficiency in english is required. Starting date: Spring 2018 Contact: Adolfo G. Grushin Institut Néel - CNRS Phone : 04 76 88 12 52 Mail : [email protected] More information: http://neel.cnrs.fr


60

Interacting topological matter out of equilibrium

General Scope : Topological phases of matter blend high-energy physics, condensed matter and the mathematical field of topology. Today a strong body of knowledge is established for interacting and non-interacting topological states in equilibrium, but there are many open questions regarding the interplay between dynamics and topology in the presence of strong electron-electron interactions. Research topic and facilities available : The successful applicant will develop a number of techniques focused, but not limited to numerical methods in condensed matter theory such as exact diagonalization and the density matrix renormalization group. These skills, together with knowledge of quantum field theory and other many-body aspects of condensed matter will be applied to the study of topological matter out of equilibrium with relevance to current experimental efforts. Possible collaboration and networking : Regular collaboration with local and international groups as well as contact with experiments is foreseen. Locally, the unique environment at Néel Institut and the CNRS campus in Grenoble is ideal to pursue collaborations and experimental input to theory. Possible extension as a PhD : A succesful M2 candidate will be encouraged to pursue a PhD studying topological matter in topics that are a natural continuation of the proposed project. The PhD will serve to broaden the skills and push the boundaries of theoretical knowledge with an abundance of state of the art techniques, both numerical and analytical. Required skills: We seek strongly motivated applicants able to work independently as well as to cooperate and communicate with other researchers and students. Together with the relevant qualifications, the applicant must be comfortable with concepts in quantum mechanics and solid state physics. Knowledge of many-body theory and programming skills such as Fortran, C, Python or Julia is desirable. Proficiency in english is required. Starting date: Spring 2018 Contact: Adolfo G. Grushin, Institut Néel - CNRS Phone : 04 76 88 12 52 Mail : [email protected] More information: http://neel.cnrs.fr


61

Spectroscopic study of free only optically trapped nanoparticles General Scope : Over the last years optical tweezers become a standard tool for non-invasive nano-manipulation in biology, chemistry, and soft-mater physics. In this context we have developed an original approach based on the use of optical fiber nano-tips and we demonstrated stable and reproducible optical trapping of micro- and nanoparticles. One major application of optical tweezers consists in the characterization of the optical properties of trapped particles, including emission spectra and optical lifetime measurements. The possibility to study free, only optically trapped particles, allows to reduce significantly any environmental influence. Moreover our specific tweezers geometry allows to capture the particle emission in three orthogonal directions, with sub-micron spatial resolution in one direction. Research topic and facilities available: The scope of the internship is to complete and optimize the spectroscopic device of our optical tweezers. Part of this task is the spectroscopic characterization of different nano-rod types of the NaYF4 family. This work will be done using the existing nano-optical fiber tweezers. First, the student has to realize optical particle trapping, including trapping stiffness measurements. In a second step, the optical properties will be studied using a spectrometer which is linked to a state-of the art EM-CCD camera. Special considerations will be given to the nano-rod emission anisotropy. To do son the fluorescence will ba captured with either the microscopy objective, one of the trapping fiber, or the third, orthogonal fiber tip. If feasible, parallel recording of at least two of these signals will be a appreciable. In a third step, she/ he will implement the emission lifetime measurement device, which is based on an elctro-optical modulator and a high speed photodiode. Finally, the obtained results will be interpreted in closed collaboration with the colleagues elaborating the particles. If available they will be compared to similar results obtained by co-focal microscopy. Possible collaboration and networking: The internship is part of the ongoing SpecTra project which is founded by the French National Research Agency (ANR). The work will be done in collabora-tion with the LPMC at Ecole Polytechnique for the nanoparticle elaboration and ICB at Dijon for theoretical considerations. Possible extension as a PhD: YES Required skills: Student should have skills in experimental work and have a background in optics and nanosciences. She/ he will get insight in the very busy domains of optical trapping and nanophysics . Starting date: free as a function of program Contact: Jochen Fick, Institut Néel - CNRS Phone: 04 76 88 10 86 e-mail: [email protected]

Nanorod trapping in our optical fiber nano-tweezres using two fiber tips. The third tip is used for the particle emission

capture.


62

Charge detection by electrostatic force microscopy in quantum devices Cadre général : Quantum point contacts (QPC) are quasi-one-dimensional channels defined by metallic gates in high-mobility semiconductor heterostructures. In addition to quantized conductance plateaus, Coulomb interactions in the channel lead to an anomalous feature below the first plateau called the “0.7 anomaly”. Despite intensive theoretical and experimental efforts during the last fifteen years, this feature still remains unexplained. To elucidate the complex interacting electron state responsible for this phenomenon, original experiments are necessary to provide new kind of information. We propose to use electrostatic force microscopy (EFM) to probe the most probable but still debated scenario of a spontaneous electron localization due the strong Coulomb interactions at low density. Combined with another technique called scanning gate microscope (SGM), we will unambiguously verify the presence of localized charges and answer this long-standing question on the most important quantum device.

Our scanning probe microscope uses a quartz tuning fork (TF) as force sensor and the sharp metallic tip from a commercial EFM cantilever. The force detection limit is in principle well below a single electron charge when the TF is at liquid helium temperature and if a cryogenic current amplifier is integrated in-situ with the TF. We will first start these EFM experiments with quantum dots (QD) where the Coulomb blockade phenomenon is well known, and then move to the puzzling case of QPC. The objective of the internship will be to optimize the force sensitivity of the EFM microscope down to a single electron charge using QD as test samples. The perspectives for a PhD thesis will be to carry out combined EFM and SGM experiments on QPC and to develop new experiments under large parallel magnetic field to probe the spin properties of the complex electron state in the QPC. Sujet exact : The master student will develop and operate the EFM and SGM experiments, combining cryogenics, electronics, and scanning probe microscopy. These complex experiments require good experimental skills and a high motivation. The devices are prepared by collaborators in Paris from high mobility GaAs/AlGaAs heterostructures. Interactions et collaborations éventuelles : Marc Sanquer (CEA, Grenoble) and Benoit Hackens (UCL, Belgium). Ce stage pourra se poursuivre par une thèse : A PhD thesis is possible if a funding is obtained. Formation / Compétences : Master in condensed matter physics and/or nanosciences. (Matière quantique, Nanophysique, etc...) Période envisagée pour le début du stage : February 2018 Contact : Hermann SellierInstitut Néel CNRS-UGA, office: D418, tel: 04 76 88 10 86 [email protected] http://www.neel.cnrs.fr/spip.php?article3282


63

Suspended graphene and nanotubes for low temperature opto-electronics General Scope: Molecular electronics provides new concepts for devices with unprecedented functionalities. Due to their low dimension, carbon nanotubes (CNTs) and graphene exhibit remarkable electronic, and optical properties allowing the transduction of optical information into an electrical one. However, their conductance is highly sensitive to their environment. For example grafting optically active molecules on nanotubes realizes an optically activated transistor. We suspend graphene and nanotubes to reach a regime of low coupling with substrate phonons and charges. This is expected to authorise the detecting of small signals for instance from molecules grafted on a single nanotube for optoelectronics at low temperature. Moreover it enables to observe, with electronic transport experiments and Raman spectroscopy, out-of-equilibrium heat transport. This regime is characterised by different temperatures of the phonons and electron baths. The electron-phonon coupling plays a major role in this regime but is not yet fully understood. It is crucial for applications to understand the nature of the coupling and whether it can be manipulated with the charge carrier density (which can be adjusted in our experiments). Research topic and facilities available:

The PhD aims at investigating the out-of-equilibrium regime in suspended nanotubes and graphene. The simplest geometry will be used at room temperature to start with: a two-laser setup will be used to heat the system while performing Raman spectroscopy at the same point (see figure). Raman imaging will provide information about spatial distribution of hot phonons and will allow inferring insights on the electron-phonon coupling, strain and heating in the system (1,2). The student will be in charge of the full spectroscopic characterization of the devices. She/He will fabricate the substrates and the development of the next substrates with electrical wiring. SimultaneousRaman spectroscopy and electron transportat the level of the single nano-object is almost unique and is highly promising. The setup in ambient conditions is fully operational. The student will participate to the development of a state-of-the-art setup operating at 10 K.

Références : (1) Cepellotti et al., Phonon hydrodynamics in two-dimensional materials. Nature Comm., 6. (2015). (2) Balandin et al., Thermal properties of graphene and nanostructured carbon materials, Nat. Mater. 10, 569 (2011). Possible collaboration and networking: The student will join the Hybrid team gathering experts in materials science, optical spectroscopy, condensed matter physics, mesoscopic transport. Close collaborations outside the lab molecular synthesis at DCM, St Martin d’Hères, photoluminescence spectroscopy at Laboratoire Pierre Aigrain, Paris, theoretical modelling at IMPMC, Paris. Possible extension as a PhD: YES Required skills: A master 2 level in Condensed Matter Physics or Nanosciences is required along with motivation for experimental work and cryogenic setup development Starting date: February/March, 2017 Contact: : Nedjma Bendiab, Laëtitia Marty Institut Néel - CNRS : [email protected] / [email protected] More information on : http://neel.cnrs.fr/spip.php?rubrique621

Figure 1: Schematic of a two lasers experiment.


64

Physicochemical characterization and image synthesis methods to generate photorealistic pictures of ancient materials

General Scope: This research topic is proposed within the framework of a cross disciplinary project which brings together research laboratories of the COMUE UGA studying ancient artworks. The main objective of this project is to use ancient materials as records of artistic habits and gestures and to investigate significant traces of the origin of the raw materials, manufacturing processes or degradation over time. This topic is more precisely at the interface between Material Science and Computing Science and aims to develop models integrating physicochemical data obtained for ancient materials to generate photorealistic pictures. Physicochemical analysis techniques will be first combined in order to obtain information allowing to precisely characterizing the interaction light/matter (exact nature of constituents, grain size and morphology, degree of structural ordering of the material, surface state, and heterogeneity of the material…). Case studies (modern materials mimicking ancient materials) will be used to optimize the analytical strategy and the algorithms, which will be lastly applied to historical samples.

Research topic and facilities available: This internship will be hosted by the Néel Institute (MRS team) in strong collaboration with the MAVERICK team (INRIA, LJK, INPG). Two tasks can be carried out according to the progress of the current projects. The M2 student will be in charge of obtaining analytical results allowing to generating pictures able to restitute: 1. Color changes of a mineral pigment when milled into powder. Hematite, Fe2O3, frequently used as red pigment, will be chosen as a case study. Powders will be milled at different grain sizes and then characterized by microcopy, spectroscopy and structural techniques. 2. Appearance of tin-based metallic decoration. This kind of decoration has been recently identified (often very degraded) on medieval sculptures (figure 1). Computer-generated pictures will have to take into account the nature of the degraded phases, their spatial organization and reproduce the appearance of the artwork for different degrees of degradation.

Figure 1. Observation by electron microscopy of a

micro-‐sample of metallic decoration (in 4, degraded tin leaf) on a wooden sculpture (Saint-‐

Jean, 1500, Le Bourget du Lac). Possible collaboration and networking: Cross-disciplinary project build on artworks and objects in the Alpine arc and bringing together research laboratories (EDYTEM, LUHCIE) and partners (ARC Nucléart, ESRF, cross border network Sculptures Alpes).

Possible extension as a PhD: yes if a funding source for a PhD thesis is obtained (research project grant or PhD contract awarded by the Physics Graduate School of Grenoble).

Required skills: - Master 2 de Recherche in physics, materials science, chemistry, or closely related science - A background in physicochemical analysis techniques (X-ray diffraction in particular) is desirable - Skills in algorithmic would be an advantage.

Starting date: February 2018

Contact: Name: BORDET Pierre / MARTINETTO Pauline, Institut Néel - CNRS Phone: 04 76 88 74 24/74 14, e-mail: pierre.bordet neel.cnrs.fr / @[email protected] More information: http://neel.cnrs.fr/spip.php?rubrique63


65

New generation of phosphors for LED lighting prepared by sol-gel method General Scope: Lighting by "white LEDs" has become a major challenge for energy saving. However, several problems need to be overcome, the most important are: cost, quality of the white photoluminescence emission and thermal stability. Currently, all devices used, or in development, involve rare earth ions whose main drawbacks are lighting with narrow emission bands with a significant blue component and also their high cost as they are highly strategic elements due to the monopoly of their production by China. At the Institut Néel, we develop a new type of phosphors based on vitreous powders to achieve white LEDs for solid lighting. The innovative character of these aluminum borate phosphors is to produce a broadband luminescence emission throughout the visible spectrum, from color centers (structural defects) in an amorphous matrix. In addition, these phosphors are made of non-toxic and abundant, no rare earth thus making them much less expensive. The project is the pursuit of original work (thesis and patent), which has been initiated in recent years. These phosphors are synthetized by two different “chimie douce” routes: - modified pechini method (polymeric precursors) - sol-gel method (alkoxide precursors); each method leading to a master topic. Research topic and facilities available: The aim of this stage are firstly: - Understanding the origin of the emitting centers, which are related to structural defects (oxygen radicals, carbon interstitials...) in order to optimize the luminescence properties. Recent results obtained by thermal analysis (TDA-TG) coupled with mass spectrometry and 13C NMR show residual carbon groups in luminescent powders. Nevertheless, one part of the residual carbons is pyrolytic carbon (aromatic carbon), which leads to partial re-absorption of the visible emitted luminescence, and thus induces a decrease of the emission intensity. Furthermore, structural studies show that the interconnected inorganic network obtained by sol-gel route retains organic moities up to high temperatures. The optimization of the synthesis of these phosphors will be performed by sol-gel route varying chemical factors. Different metals with lower coordination number and stoichiometric ratios of molecular precursors (allowing metal complexation and polymerization of organic-inorganic network) will be tested. The change of chemical composition should enable to adjust the width of the spectral emission of luminescent for better colorimetry. A study of the different parameters of thermal treatments (heating rates, the ranges of temperature, controlled atmosphere during treatment), which are at the origin of the presence of emitting centers should be clarify. Finally, the understanding of the origin and role of emitting centers and the structural characterizations and modeling of the amorphous phase will be implemented by coupled spectroscopic studies: FTIR, UV-Vis spectroscopy, EPR, NMR, X-ray diffraction and X-ray scattering.

Possible collaboration and networking: Institut de Recherche Chimie-Paris ; INAC-CEA Grenoble Possible extension as a PhD: Yes Required skills: Chemistry in solution, knowledge on physicochemical and structural characterizations of material Contact : Pr Gautier-Luneau Isabelle Institut Néel – CNRS Phone: 04 76 88 78 04 e-mail: [email protected] More information: http://neel.cnrs.fr


66

Pressure as a way to control the coupling between magnetic and electric properties

General Scope: The magneto-electric effect couples the magnetic and electric properties of a compound. It thus allows to control one type of property while acting on the other one. For instance, it is possible to modify a system polarisation using an applied magnetic field or to control the system magnetisatiob by the application of an electric field. These multifunctionnal compounds are called multiferroics and are attracting a lot of attention both in the field of fundamental research (one need to understand the fundamental mechanisms) and in the field of applied physics (for instance in microelectronics, componants design, data storage, spintronics, micro-wave componants, etc.). The magneto-electric compounds are few, the coupling often weak and working at below room temperature. It is thus of utter importance to understand the fundamental mechanism at the orgin of both the coupling and its amplitude. Recent work showed that the application of external contraints such as pressure may strongly modify the magneto-electric properties of a system. THis work opened numerous fundamental questions. Why? How? Can we control this effect? Does pressure acts only on the magneto-electric coupling amplitude or on its existence itself? etc...

Temperature–pressure phase diagram of the magnetic model of CuO. Nature Com. 4,

2511 (2013). Research topic and facilities available: The objective of the present theoretical intership will thus be to contribute to answer theses questions by the calculation of the magneto-electric coupling as a function of pressure on a typical system. The student will thus

• learn the theoretical foundations of themagneto-electric coupling calculation • learn the basis of electronic struture calculations • learn how to use the supercomputers accessible in the national computation centers • learn how to extract the important information from the calculation in order to built a model.

For this purpose the student will have access to national and local computer centers. Possible collaboration and networking: The student will collaborate with other theoreticians from the Neel Institut or the Laue Langevin Institut. According to the work progress she/he may collaborate with theoreticians working on the same coupounds and discuss with experimentalists performing polarisation measurements or magnetic structure determination. Possible can be extended as a PhD. Required skills: The student should have a good knowledge of quantum mechanics, as well as knowledge of computers usage. Starting date: between January and March 2018 Contact: Name: Lepetit Marie-Bernadette Institut Néel - CNRS Phone: +33 4 76 88 12 89e-mail: [email protected] More information: http://neel.cnrs.fr


67

La pression comme contrôle du couplage entre propriétés magnétiques et électriques

Cadre général : L'effet magnéto-électrique couple les propriétés magnétiques et électriques d'un matériau. Il permet donc de contrôler une propriété en agissant sur l'autre. Par exemple il est possible de modifier la polarisation d'un système par l'application d'un champ magnétique ou inversement l'aimantation par l'application d'un champ électrique. Ces systèmes multifonctionnels sont dits multiferroïques et attirent beaucoup d'attention tant dans le domaine de la recherche fondamentale (il faut comprendre), que dans celui des applications (micro-électronique, conception de composants, stockage de données, électronique de spin, composants micro-onde, etc.). Les composés magnéto-électriques sont peu nombreux, les couplages en général faibles et les domaines de températures où le couplage existe en général bien en dessous de la température ambiante. Il est donc crucial de comprendre tant les mécanismes microscopiques responsables de l'existence d'un couplage, que les raisons qui font que celui-ci est de grande amplitude à une température donnée. Des travaux récents montrent que l'application de contraintes extérieures peut notablement influer sur ces propriétés. C'est par exemple le cas de la pression.

Diagramme de phase temperature–pression pour le modèle de

CuO. Nature Com. 4, 251 (2013). Sujet exact, moyens disponibles : L'objectif de ce travail théorique sera donc de poser les jalons du calcul du couplage magnéto-électrique en fonction de la pression dans un cas modèle. L'étudiant devra donc

• s'initier au calcul aux bases théoriques sous tendant le calcul du couplage magnéto-électrique • s'initier aux techniques du calcul de structure électronique • apprendre à utiliser les super-calculateurs des grands centres de calcul nationaux • apprendre à extraire l'information pertinente des calculs et à la modéliser.

Pour cela l'étudiant aura accès aux centres de calcul intensifs régionaux et nationaux. Interactions et collaborations éventuelles : L'étudiant sera amené à travailler avec d'autres théoriciens de l'institut Néel ou du groupe de théorie de l'Institut Laue Langevin. Selon l'avancement de ses travaux il pourra aussi collaborer avec d'autres groupes de théoriciens travaillant sur la même famille de composés et discuter avec les expérimentateurs spécialistes des mesures de polarisation ou de structure magnétique. Ce stage pourra se poursuivre par une thèse Formation / Compétences : L'étudiant devra avoir une bonne connaissance de la mécanique quantique ainsi que des connaissances de base en informatique. Période envisagée pour le début du stage : entre janvier et mars 2018 Contact : Lepetit Marie-Bernadette Institut Néel - CNRS : tél 04 76 88 12 89 mel : [email protected]


68

Impact du soufre sur le comportement des platinoïdes dans les fluides géologiques

Cadre général : Le but du stage est de mieux quantifier le rôle des fluides hydrothermaux riches en soufre dans le transport de certains métaux critiques comme les Platinoïdes (PGE) et la formation de leurs dépôts économiques. La crise des métaux depuis la dernière décennie fait apparaître un besoin rapidement croissant en certains métaux de haute valeur technologique dont les ressources actuelles connues sont très limitées. Ce besoin a généré un intérêt croissant des scientifiques et industriels pour identifier de nouvelles sources de ces métaux appelés ‘critiques’ et de mieux les extraire de leurs minerais. La plupart des métaux critiques sont étroitement associés au soufre dans les minerais hydrothermaux et magmatiques, mais le rôle du soufre dans le transport de ces métaux par les fluides qui ont formé ces dépôts est très peu connu faute de données expérimentales et analytiques sur la phase fluide elle-même. En particulier, l’impact de nouvelles formes de soufre, les ions radicalaires trisulfure S3

- récemment découverts aux conditions des fluides métallifères, sur la mobilisation et le fractionnement des métaux chalcophiles demeure complètement inconnu. Sujet exact, moyens disponibles : Il s'agira d’élucider les relations des PGE avec le soufre en phase fluide HP-HT sur l’exemple du platine, via une approche combinée expérimentale, spectroscopique et de modélisation. En particulier, nous essayons de tester l’effet des ions radicalaires de soufre sur le transport du Pt par les fluides hydrothermaux. Des expériences de spectroscopie d’absorption X sur synchrotron (Grenoble) programmée en février 2018 permettra de mesurer la solubilité et la spéciation chimique (état redox, ligands) du platine en fonction de la composition du fluide, de la température et de la pression. A partir de ces données, une modélisation des interactions fluide-roches sera effectuée afin d’évaluer les phénomènes qui contrôlent le transport et la précipitation du platine par les fluides géologiques. Interactions et collaborations éventuelles : Depuis 5 ans, nous menons des études concertées visant à mieux comprendre le rôle des différentes formes chimiques de soufre sur les transferts des métaux et la formation de leurs ressources économiques. Le présent sujet de Master s’intègre dans ces études et sera mené dans le cadre du projet ANR RadicalS (http://www.get.obs-mip.fr/recherche/projet/radicalS) regroupant l’Institut Néel/ESRF (Grenoble), GET (Toulouse) et l’IMPMC/ENS (Paris). Des collaborations internationales sont envisagées avec l’Université de Toronto et l’Université de Potsdam. Ce stage pourra se poursuivre par une thèse sur un sujet plus étendu à partir d'octobre 2018. Formation / Compétences : Ce stage s’adresse à des candidats intéressés par les processus hydrothermaux en général et l'expérimentation. Les candidats devront avoir doivent de bonnes bases en physique et posséder de bonnes connaissances en chimie de la solution aqueuse. Période envisagée pour le début du stage : février-juillet 2018, la majeure partie de ce stage se déroulera à Toulouse au sein du GET. Contact : Hazemann J-Louis Institut Néel 04 76 88 74 07 [email protected], Pokrovski Gleb , [email protected]; tél.: 0561332618


69

Epitaxial Superconducting Quantum NanoWiresTexte sur une page avec figures pour la totalité du sujet de Master 2 en explicitant :

Scientific Context: During the last decade, it has been demonstrated that superconducting Josephson quantum circuits constitute ideal blocks to build quantum bits and to realize quantum mechanical experiments. These circuits appear as artificial atoms whose properties are fixed by electronics compounds (capacitance, inductance, tunnel barrier)[1]. Up to now only aluminum polycrystalline films were used to realize the superconducting quantum circuits. These films present poor structural and electrical properties (superconducting films in the dirty limit, amorphous tunnel barrier in the Josephson junctions, amorphous native oxide…), which could limit the quantum coherence in the experiments. High quality epitaxial thin films can overcome this limitation.

During the last years, through a collaboration between NEEL and SIMAP (B. Gilles team), we have successfully developed and characterized very high quality epitaxial superconducting films of rhenium. These films present very low density of defects and impurities leading, as example, to very long mean free path for the electrons and to the absence of native oxide[2]. This opens new possibilities to build superconducting quantum circuits based on nanowires. In our team we have developed original microwave quantum optics experiments coupling artificial atoms and microwave resonators[2] and we want to develop a novel generation of circuits based on such high quality material.

Figure: Epitaxial rhenium films with atomic terraces growth by MBE in SIMAP (B. Gilles).

[1] E. Dumur et al., “V-shaped superconducting artificial atom based on two inductively coupled transmons,” Phys. Rev. B, vol. 92, no. 2, Jul. 2015. [2] E. Dumur, et al, “Epitaxial rhenium microwave resonators”, IEEE on Applied Superconductivity, 26, 1501304, 2016.

Description, means available: The PhD student will fabricate and study novel superconducting quantum nano-circuits based on epitaxial rhenium films. In particular we plan to study ultra thin films (few nanometers thick) and superconducting nano-wires in which quantum fluctuations and nonlinearity effects could emerge. In addition he will characterize microwave coplanar waveguide resonators for circuit QED experiments. The epitaxial films will be grown in two Molecular Beam Epitaxy equipments in SIMAP and in NEEL. The nano-fabrication using lithography processes will be developed in NanoFab and PTA facilities. She/He will then carry out the dc and microwave measurements of the device at very low temperature to characterize and analyze the properties of the device. Our team has a strong experience in nanofabrication, microwave electronics, cryogenic equipment and superconducting qubit experiments. Interactions and collaborations: Our team is part of several national networks. We are strongly collaborating with Bruno Gilles in SIMAP for the epitaxial growth of rhenium thin films. This project is financially supported by the National French Funding Agency (ANR). The PhD student will also collaborate with other teams to build novel quantum devices based on epitaxial rhenium films. Education / Profile: Master 2 or Engineering degree. We are seeking highly motivated students who want to develop novel superconducting quantum circuits based on very high quality epitaxial films. Possible extension as a PhD: Yes. PhD Funding: Possible funding through the Grenoble Quantum Engineering PhD Calls(https://quantum.univ-grenoble-alpes.fr/) Contact: BUISSON Olivier and NAUD Cécile Institut Néel- CNRS : phone: +33 4 56 38 71 77 email: [email protected], [email protected] More informations on : http://neel.cnrs.fr



70

Superconducting qubits

Scientific Context: During the last decade, it has been demonstrated that superconducting Josephson quantum circuits constitute ideal blocks to build quantum bits and to realize quantum mechanical experiments. These circuits appear as artificial atoms whose properties are fixed by electronics compounds (capacitance, inductance, tunnel barrier) [1]. By adjusting and optimizing these parameters, we are able to build superconducting qubits with long coherence times and to manipulate its quantum state (Figure). Up to now the readout is still suffering from some limitations. We propose to study, develop and optimize a novel readout able to reach quantum non-demolition measurements with a high fidelity, as proposed theoretically [2].

Figure: Rabi oscillations of our superconducting qubit: its quantum state oscillates between its ground state |g> and first excited state |e> and can be controlled by fixing the waiting time.

[1] “V-shaped superconducting artificial atom based on two inductively coupled transmons,” E. Dumur et al., arXiv:1501.04892, Phys. Rev. B 92, 020515(R) (2015).

[2] “Ultrafast QND measurements based on diamond-shape artificial atom”, I. Diniz, E. Dumur, O. Buisson and A. Auffeves. Phys. Rev. A 87, 033837 (2013).

Description, means available: Our team has a strong experience in nanofabrication, microwave electronics, cryogenic equipment and superconducting qubit experiments. The student will fabricate the artificial atom through nanofabrication using lithography processes in NanoFab and PTA facilities. She/He will then carry out microwave measurements in the quantum limit of the device at very low temperature. All the microwave equipments as well as the dilution fridge are already installed. The student will participate to the understanding and improvement of the quantum non-demolition measurements Interactions and collaborations: Our “Quantum Coherence” team is part of several national networks. This project on superconducting qubits has just been financially supported by the National French Funding Agency (ANR) and the student will collaborate with Quantronics team in CEA-Saclay. Possible extension as a PhD: Yes. Required skills: Master 2 or Engineering degree. We are seeking highly motivated students on quantum mechanics who want to develop experiments on quantum bits. PhD Funding: Possible funding through the ANR project and the Grenoble Quantum Engineering PhD Calls(https://quantum.univ-grenoble-alpes.fr/)

Contact: BUISSON Olivier Institut Néel- CNRS : phone: +33 4 56 38 71 77 email: [email protected] More informations on : http://neel.cnrs.fr



71

Theory and experiments on magnetic skyrmions General Scope: Skyrmions, described originally by Skyrme1 in 1962, are topological solitons localized in space and which present particles-like properties: they have quantized topological charges, interact via attractive and repulsive forces, and can condense into ordered phases. The concept of skyrmions has spread over various branches of physics including condensed matter as for example the case of liquid crystals, quantum Hall magnets and Bose-Einstein condensates. In ferromagnets, skyrmions used to be called two-dimensional (2D) topological solitons or magnetic vortices and their existence has been predicted more than 40 years ago. However, due to several factors, their experimental observation is much more recent. The potentialities of these magnetic solitons to serve as information carriers in future technologies has driven a strong recent development of experimental and theoretical studies in this fiels[1,2]. [1] Topological properties and dynamics of magnetic skyrmions, N. Nagaosa (2013) [2] Focus on Magnetic Skyrmions, New Journal of Physics (2017)

Research topic and facilities available: In the Micro and Nanomagnetism Group from Institut Néel, we are specialized in theoretical modeling and experimental characterisations of magnetic nanostructures. We have developed in the past few years a strong expertise in the field of skyrmionics which makes us part of the world’s physics groups specialized in this subject as attested by our participation to several national and international research grants and conferences. In particular we have developed techniques to observe and control magnetic skyrmions[3.4] and we are using and developing numerical simulations based on micromagnetic and analytical theoretical models for skyrmions. The student will work on this very exciting and competitive framework on the latest advances on skyrmion modelisation and observation using techniques such as Magneto Optical Microscopy, Magnetic Force Microscopy and topological Hall effect. [3] Room-temperature chiral magnetic skyrmions, Nature Nanotechnology (2015) [4] The skyrmion switch, Nanoletters (2017) Possible extension as a PhD: Yes Contact: Name: Anne Bernand-Mantel, Laurent Ranno Institut Néel - CNRS e-mail: [email protected] More information: http://neel.cnrs.fr/spip.php?rubrique52&lang=en



72

Long range electron-electron interactions and charge frustration General Scope: In condensed matter, frustration --- the impossibility to satisfy certain physical constraints imposed to the elementary constituents --- leads to the emergence of original and often complex states: in magnetic systems, for instance, the frustration of spin-spin interactions can lead to spin liquid and spin glass phases, and to the appearance of collective excitations such as magnetic monopoles. Frustration is also responsible for the residual entropy of water ice at the absolute zero. While theoretical and experimental studies on the subject mostly focus on magnetic systems, charge frustration is also being explored, leading to the emergence of new phases and concepts: a charge glass phase has been recently observed experimentally in two-dimensional molecular conductors, and the quest for its quantum analogue --- the Pinball Liquid --- is underway.

Figure: an illustration of possible local constraints leading to spin (left) and charge (right) frustration.

Research topic and facilities available: During this internship, we propose to study theoretically electronic models with long range Coulomb interactions on low-dimensional frustrated lattices. The student will explore the emergence of collective excitations in strongly interacting electron systems as well as the possible realization of non-conventional quantum states. The models developed to this scope will be analyzed using appropriate many-body approaches, both analytical (perturbation theory in the strong coupling limit, random phase approximation) and numerical (extended dynamical mean field theory, exact diagonalization, classical and quantum MonteCarlo simulations). The student will have the opportunity of learning frequently used techniques in condensed matter theory, while at the same time getting acquainted with a currently expanding research topic. Possible collaboration and networking: Possible extension as a PhD: YES Required skills: Solid basis in condensed matter theory, scientific programming, strong motivation. Starting date: March 2018 Contact: Name: Simone Fratini / Arnaud Ralko Institut Néel - CNRS Phone: 0456387141 e-mail: [email protected] [email protected] More information: http://neel.cnrs.fr



73

Fluctuations hydrodynamique en conditions extrêmes Cadre général : De tous les fluides, l’hélium cryogénique est celui présentant la plus faible viscosité. Cette propriété est mise à profit en laboratoire pour produire des états turbulents très intenses, inaccessibles aux expériences traditionnelles. L’enjeu consiste à tester les théories de la turbulence dans des conditions optimales. Récemment, les expériences GReC et SHREK, ont permis d’atteindre en conditions de laboratoire des intensités turbulentes record (nombre de Reynolds > 107). Un dernier défit majeur consistait à inventer un anémomètre capable de résoudre les plus petites échelles de l’écoulement, soit quelques microns. Au terme de plusieurs années de développement, un premier capteur fonctionnel est désormais micro-fabriqué (cf photo).


Nous souhaitons recruter un étudiant (stage + thèse) qui participera aux futures campagnes de mesure et conduira l’analyse physique des données turbulentes. Concrètement, une partie du travail sera consacrée à l’instrumentation (micro-fabrication, électronique) et à la mise en œuvre de l’expérience (acquisition de données,…). L’autre partie sera consacrée à l’analyse des données, et en particulier aux tests des lois de turbulence à très haut nombre de Reynolds (statistique des fluctuations de vitesse et de température).

L’activité est basée à Grenoble, avec des séjours courts au CERN. Interactions et collaborations éventuelles : L’expérience GReC est menée en collaboration avec le CERN. L’expérience SHREK résulte d’une collaboration avec d’autres laboratoires français : LEGI, ENS-Lyon, SPEC et SBT/INAC (ANR Ecouturb).

Ce stage pourra se poursuivre par une thèse : Oui Formation / Compétences : Compétences développées: Instrumentation & Mesures bas bruit, Hydrodynamique & Turbulence, Physique des basses températures & Cryogénie, Nanotechnologie & Technique de microfabrication, Acquisition & Traitement du signal. Période envisagée pour le début du stage : indifférente Contact : Roche Philippe, Institut Néel – CNRS/ Université Grenoble-Alpes [email protected] (04 76 88 11 52)http://hydro.cnrs.me

T

Expérience GReC, situé au CERN Jet d’He à 5K de 1m de diamètre



74

Turbulence Quantique : étude expérimentale Cadre général : En dessous de 2,17 K, l’hélium liquide acquiert des propriétés superfluides : il peut s’écouler sans viscosité et la vorticité de son champ de vitesse devient quantifiée. On s’attend donc à ce que sa turbulence, appelée « Turbulence Quantique », diffère de la turbulence « classique ».

D’après plusieurs études récentes, il semble que la principale différence soit concentrée au niveau des plus petits tourbillons présents dans ces deux types de turbulence. En effet, en l’absence d’une dissipation efficace, on s’attend à ce que les tourbillons superfluides s’accumulent aux petites échelles de l’écoulement.

L’objectif est de détecter et comprendre cette différence, grâce à un détecteur conçu à cet effet.


Dans le cadre du stage et de la thèse, l’étudiant optimisera un capteur ultra-miniaturisé (<200 "m) de vortex quantiques, en tirant profit de l’environnement grenoblois en nano-technologies (nanofab, PTA/Minatec). Ce capteur sera ensuite exploité dans nos différents écoulements d’hélium superfluide. L’un de ces écoulements sera la soufflerie TOUPIE, spécialement construite pour répondre à cet objectif, et qui bien vient de bénéficier d’un upgrade pour atteindre des températures approchant 1K, un record pour une soufflerie cryogénique de grande taille. Un autre écoulement, alimenté par deux pâles contra-rotatives, est offert par l’expérience collaborative SHREK.

Interactions et collaborations éventuelles : Le projet s’inscrit dans le cadre du projet inter-laboratoires autour de l’expérience SHREK (projet ANR Ecouturb, (CEA/CNRS/ENSL/INP/UJF)), centré sur l’étude des couches limites superfluides.

Ce stage pourra se poursuivre par une thèse : Oui Formation / Compétences développés : Hydrodynamique & Turbulence quantique, Physique des basses températures & Cryogénie, Nanotechnologie & Technique de microfabrication, Acquisition & Traitement du signal, Instrumentation & Mesures bas bruit Période envisagée pour le début du stage : indifférente Contact : Roche Philippe, Institut Néel – CNRS/ Université Grenoble-Alpes [email protected] (04 76 88 11 52)http://hydro.cnrs.me

T

Tube de Pitot miniaturisé permettant la mesure de

fluctuations de vitesse superfluide

Tourbillons superfluides (simulation)



75

Convection naturelle aux nombres de Rayleigh extrêmes Cadre général : Depuis sa première observation, il y a une quinzaine d’années par notre équipe, le « Régime Ultime de la convection » est devenu l’objet d’une riche polémique scientifique.

Ce régime transporte la chaleur bien plus efficacement que tout autre, et semble confirmer un modèle théorique vieux d’un demi siècle et prédisant l’existence d’un régime entièrement turbulent.

Toutefois, les conditions qui permettent le déclenchement de ce régime échappent toujours à la compréhension, malgré la mise

en œuvre de moyens expérimentaux et numériques très importants dans une dizaine de pays.

Notre objectif est d’identifier la nature de l’instabilité favorisant la transition. Pour cela, nous tirons profit des propriétés uniques de l’hélium cryogénique pour atteindre des nombres de Rayleigh extrêmes.

Sujet, moyens disponibles : Dans le cadre du stage, l’étudiant travaillera sur une nouvelle cellule de convection dont la géométrie sphérique (boule de cuivre surchauffée, cf photo) permet de l’affranchir des fluctuations du « vent » présent dans les cellules traditionnelles de Rayleigh-Bénard.

Le but sera de se placer juste en dessous du régime ultime et d’identifier les évènements précurseurs annonçant la proximité avec la transition. Interactions et collaborations éventuelles : Le projet s’inscrit aussi dans le cadre d’une collaboration entre plusieurs laboratoires grenoblois sur les évènements extrêmes.

Ce stage pourra se poursuivre par une thèse : oui. Dans le cadre de la thèse, une camera mesurant les fluctuations de flux thermique sera développée en tirant profit des techniques de micro-fabrication. L’objectif sera d’identifier la nature du mécanisme de la transition vers le régime ultime de la convection. Formation / Compétences : Compétences développées: Instrumentation & Mesures bas bruit, Hydrodynamique & Turbulence,

Physique des basses températures & Cryogénie, Acquisition & Traitement du signal. Et durant la thèse : Nanotechnologie & Technique de micro-fabrication, Période envisagée pour le début du stage : indifférente Contact : Roche Philippe, Institut Néel – CNRS/ Université Grenoble-Alpes [email protected] (04 76 88 11 52) http://hydro.cnrs.me

C

Cellule de convection sphérique fonctionnant entre 4 K et 10 K



76

Mesure de fluctuations de vitesse par anémométrie à fibre optique Cadre général : La physique de la turbulence est étudiée depuis plus d’un siècle mais elle demeure un sujet ouvert. Au sein d’un écoulement turbulent, des tourbillons de tailles différentes interagissent. L’étude de ces interactions entre structures et la compréhension des caractéristiques des très petites échelles constitue un défi majeur qui nécessite la miniaturisation des sondes de mesure. Les capteurs doivent être suffisamment petits pour résoudre les plus petites structures tout en étant robustes et sensibles. Dans cet esprit, nous avons entrepris à l’Institut Néel le développement d’un anémomètre à fibre optique. Les premiers essais ont montré que le principe de fonctionnement de la sonde est valide (voir Figure). Un nouveau prototype est en cours de réalisation. Afin de permettre l’exploitation de la sonde, il est maintenant important de caractériser sa réponse dans un écoulement.

Fig. [à gauche] L’écoulement arrive par la gauche et défléchit la membrane. Son déplacement est mesuré par la fibre optique (d’après Watson et al.) [à droite] Capteur commercial à fibre (FISO).


Nous souhaitons accueillir un étudiant pour caractériser cette sonde. Pour cela, un écoulement d’air comprimé filtré sera utilisé pour produire un signal de turbulence connu, la sonde étant montée sur une tête goniométrique. L’étudiant devra monter le banc de test et l’instrumenter. Il étudiera ensuite la réponse dynamique de la sonde en fonction de l’angle d’incidence. Le traitement des données devra permettre de caractériser les performances de la sonde. De ce travail dépendra la nouvelle génération de ce type de capteur. Interactions et collaborations éventuelles : L’anémomètre est développé au sein d’une collaboration interne à l’Institut Néel, entre des hydrodynamiciens et des opticiens. L’étudiant sera amené a interagir pleinement avec les différents acteurs de la collaboration. Il devra également collaborer avec les équipes techniques du laboratoire pour les questions de mécanique.

Ce stage pourra se poursuivre par une thèse : OuiLa thèse tirera profit de ce type de capteur fibré, ainsi que d’un autre anémomètre à micro-film chaud, pour étudier les processus à petites échelles dans des écoulements turbulents extrêmement intenses d’hélium cryogénique, superfluide ou pas. Formation / Compétences : Compétences développées: Optique fibrée, Instrumentation, Hydrodynamique & Turbulence, Acquisition & Traitement du signal. Période envisagée pour le début du stage : indifférente Contact : Roche Philippe, Institut Néel – CNRS/ Université Grenoble-Alpes [email protected] (04 76 88 11 52) http://hydro.cnrs.me (contacts alternatifs : Jochen Fick, [email protected] )



77

Thermal expansion in rare-earth cage systems General Scope: Atoms from the lanthanide series are characterized by an unfilled 4f shell, resulting in their ability to carry a magnetic moment, as well as multipolar electric moments. The latters reflect the asphericity of the 4f electrons distribution. This possibility of a redistribution of the 4f shell electronic density is involved in many important phenomena that develop in rare-earth systems: crystal field scheme, magnetic anisotropy, magnetoelastic phenomena. . . If the rare-earth occupies a site of high point symmetry, the 4f distribution will be also highly symmetrical. However, at low temperature, the slightest distortion of its environment will have a drastic effect on the 4f distribution, lowering the electrostatic energy: the system is the siege of a Jahn-Teller instability. Research topic and facilities available: There exists rare-earth compounds in which the magnetic ion is enclosed in an oversized cage. In such an environment, the easiest way engaging the Jahn-Teller instability is a movement of the rare-earth out of the cage center (see figure above). This should result in a specific, low temperature, thermal variation of the rare-earth distribution inside the cage. Among other consequences, this will reflect on the crystal volume within the paramagnetic range. These predictions can be put to test by measuring the thermal expansion of cage compounds in the temperature range of interest, typically below 50 K. We thus propose to investigate the thermal expansion of some rare-earth compounds from the hexaborides and filled skuterrudites series. Specific heat measurements will be carried out as well, since they parallel the thermal expansion: the splitting of the rare-earth electronic ground state is directly related to the magnetic entropy. Infrared spectroscopy measurements are also considered. The main experimental effort will be focused on the thermal expansion measurement setup, which requires some refinements in order to achieve optimal sensitivity. On the theoretical side, the quantum mechanics treatment requires modelling of the cage potential well, with appropriate dynamic approximations. One has to describe how the shape of the potential well can change with the temperature. To describe the expansion and other magnetoelastic properties, the cage and its magnetic guest must be considered elastically coupled with their environment. Possible collaboration and networking: Collaboration within the institute in the MCBT department and MagSup team. Collaboration with Dr N. Shitsevalova (Ukraine) for the samples preparation. Possible extension as a PhD: Yes, but financial support to be found. Required skills: Basic academic knowledge in solid state physics and magnetism. Experimental skills as well as some computer programming experience (labview for setup control and other language for calculation/data analysis). Starting date: Spring 2018 Contact: Mehdi AMARA, Institut Néel - CNRS Phone: 0476887913 e-mail: [email protected] More information: http://neel.cnrs.fr

Illustrative scheme showing the Jahn-Teller

symmetry lowering for an off-center rare-earth in a cage. The 4f ground state of energy E4f is

split, while the 4f distribution reorganises.



78

Molecular spin devices for quantum processing General Scope: The realization of an operational quantum computer is one of the most ambitious technological goals of today’s scientists. In this regard, the basic building block is generally composed of a two-level quantum system (a quantum bit). It must be fully controllable and measurable, which requires a connection to the macroscopic world. In this context, solid state devices, which establish electrical connections to the qubit are of high interest. Among the different solid state concepts, spin based devices are very attractive since they already exhibit long coherence times.

Electrons possessing a spin 1/2 are conventionally thought as the natural carriers of quantum information, but alternative concepts make use of the outstanding properties of molecular magnets as building blocks for nanospintronics devices and quantum computing. Their spin benefit from longer coherence times compared to purely electronic spins. In this context, our team combines the different disciplines of spintronics, molecular electronics, and quantum information processing. In particular, we fabricate, characterize and study molecular spin-transistor in order to manipulate[1] and read-out an individual spin[2] to perform quantum operations[3]. [1] S. Thiele, F. Balestro, R. Ballou, S. Klyatskaya, M. Ruben, W. Wernsdorfer, Science 2014. [2] R. Vincent, S. Klyatskaya, M. Ruben, W. Wernsdorfer, F. Balestro. Nature 2012. [3] C. Godfrin, R. Ballou, S. Klyatskaya, M. Ruben, W. Wernsdorfer, F. Balestro, Phys. Rev. Lett. 2017. Research topic and facilities available: Nano-devices addressing single molecular spins will be designed and reliable methods for their realization and caracterization will be developed. Our team has a strong experience in molecular magnetism, nanofabrication, ultra-low noise transport measurements, microwave electronics and cryogenic equipment. We propose to use molecular spins as platform to perform multiqubit algorithms. Single molecular units are embedded in scalable electronic circuits and individual spin read out is performed by molecular (or carbon-based) quantum dots. The key experiment will be the demonstration of two qubit gate to complete the set of universal gates for scalable architectures. The student will fabricate the samples using the clean room facilities of the Néel Institut. She/he will carry out the measurements of the device at very low temperature (20mK), using one of the six fully equipped dilution refrigerators of the team, in order to create, characterize and manipulate single spin using spin based molecular quantum dot. Possible collaboration and networking: This multidisciplinary research field is based on years of collaborations with teams from different scientific and technical cultures (cleanroom, technicians, collaborations with chemists and theoreticians, ...), in the framework of European projects and different national and regional funding. Possible extension as a PhD: Yes Required skills: We are looking for a motivated student who is interested in experiments that are challenging from the experimental point of view. Starting date: Contact: BALESTRO Franck, Institut Néel - CNRS - UGA Phone: 04 76 88 79 15 e-mail: [email protected] More information: http://neel.cnrs.fr/spip.php?rubrique51



79

Cavitation at the nanoscale Keywords: statistical physics, porous materials, helium, low temperature, optics General Scope: Cavitation, i.e. the formation of a vapor bubble in a stretched liquid, is of fundamental interest. For decades, the consensus has been that, in bulk liquid, cavitation occurs via the stochastic formation of a bubble nucleus as described by the classical nucleation theory. We want to elucidate whether this also holds for liquids confined at the nanoscale. Research topic and available facilities: Cavitation takes place when liquids are in a metastable state below their saturated vapor pressure. It is possible to reach this state through active techniques such as ultrasonic waves or intense mechanical stirring. Alternately, natural evaporation in trees drives their sap to large negative pressures, eventually triggering adverse cavitation. This inspired a different route to study cavitation, namely the ‘synthetic tree’ concept (Cornell University): liquid is condensed in a cavity connected to a vapor reservoir through a narrow neck also filled with liquid. When pressure in the vapor reservoir is reduced, the liquid inside the cavity reaches a deep metastable state (see fig a).

Our project aims to develop this idea for nanometric-size cavities etched in alumina membranes. In collaboration with L. Cagnon (Neel), we already master the fabrication of individual nm-diameter cylindrical pores in such membranes (fig b), where they self-assemble in hexagonal arrays (fig c). To define the cavities, we are currently working to change the diameter of the pores during the growth process. The task of this intership will be to study the first samples using imaging and adsorption techniques (fig d). This preliminary step opens to a thesis where a combination of cryogenic and optical tools will be used to track the occurrence of cavitation as a function of the geometry of the cavities and the thermodynamic state of the fluid. The team Our team works at the crossroads of low temperature and statistical physics, focusing on porous materials. We use an original approach where the fluid of interest is helium, taking advantage of its unique properties compared to other fluids. Possible collaboration and networking This work is part of a new collaborating project supported by ANR. In this framework, the PhD student will participate to experiments using complementary techniques and fluids at Ecole Normale Supérieure (LPS-ENS, Paris) and Université Pierre et Marie Curie (INSP). Possible extension as a PhD: yes Required skills: the candidate should have a solid background in condensed matter, while a good knowledge in optics would be a plus. Skills (or motivation) in programming and numerical simulation would be appreciated. Starting date: from January to March 2018 Contact: Panayotis Spathis / Pierre-Etienne [email protected] / [email protected] For more information:

- on the ‘artificial tree’ concept : http://www.stroockgroup.org/home/research - on the fabrication process : http://neel.cnrs.fr/spip.php?article2056&lang=fr

on the team : http://neel.cnrs.fr/spip.php?rubrique162 or better: drop by the lab



80

Functionalization of suspended thermoelectric nano-generators General Scope: With the emergence of Industry 4.0, the possibility for wireless sensors to harvest small quantities of energy (100 "W – 1 mW) in their environment for becoming autonomous is attracting a lot of attention from both the scientific community and the economic world. Among different sources of energy, thermal energy presents the advantage to be available almost everywhere but in small quantities. To adress the challenge of thermal energy harvesting, we have developed a planar thermoelectric generator. It is made of suspended membranes which are very sensitive to small intermittent temperature gradient thank to their very low mass.

Research topic and facilities available: The expertise developed at the Institut Néel in the development of suspended sensors dedicated to thermal measurements at very low temperatures has been used to design a suspended thermoelectric nano-generator. The duplication of this thermoelectric nano-module thanks to standard clean room techniques enabled us to power sensors and to transmit the information using low power wireleess protocol (see figure 1). The main goal of the internship would be to use the suspended membranes as a support for the deposition of an active thin film giving to the device another features. It could magnetic materials for sensing magnetic fields variation and/or phase change material (PCM) for stocking energy and rereleasing it when the temperature of the device is going down a given value. Possible collaboration and networking: A start-up exploiting these patents is going to be created. Today, three companies (SNCF, Air Liquide and Schneider Electric) are working with us for applications of the energy harvesting system. The team is involved in French and European network of thermal engineering. Possible extension as a PhD: The internship could be followed by a PhD Required skills: A Master level in applied physics is required. Starting date: Spring 2018 Contact: Name: Dimitri Tainoff Institut Néel - CNRS Phone: 04 76 88 12 17 e-mail: [email protected] More information: http://neel.cnrs.fr

Figure 1 : SEM image of an individual micro-thermogenerator. The membrane is suspended and a functional material having phase transition will be deposited at its center to reach new properties. The micro-generator are then duplicated and integrated into small prototypes built in the frame of collaboration with industrial partners.



81

Fig. 1: Free energy of the superconducting state versus the superconducting order parameter (Re(!),Im(!)). There are two types of fundamental collective excitations. One, the amplitude Higgs mode, is the analogous of the Higgs boson.

Superconducting Higgs mode General Scope: When a spontaneous breaking of a continuous symmetry takes place, for instance when crossing the normal to superconducting transition, collective excitations of the order parameter emerge: They are the phase modes and the massive amplitude Higgs mode, as illustrated Fig.1. While the quest for the Higgs boson in particle physics has reached its goal and its prediction has been rewarded with the Nobel Prize, there is growing interest in the search for analogous excitation in quantum many body systems, notably in superconductors. Indeed, even if theoretically always here in any superconductors and even if presented as a textbook excitation, this ‘dark’ mode (like the Higgs boson in particle physics) remains very elusive. In principle, it does not couple to any external probe. Our purpose is to identify this Higgs mode in compounds where such excitation has been claimed to be present and to search for new Higgs mode in new compounds, in order to provide some textbook examples.

Research topic and facilities available:

The compounds where a superconducting Higgs mode has been claimed to be present are the ones where superconductivity coexists with another type of electronic order, such as charge density wave. In these systems, like in NbSe2 (see Fig. 2), the amplitude oscillations of the CDW order parameter (CDW mode) can be detected by Raman spectroscopy. When the system becomes superconductor, a new Raman peak emerges. It has been attributed to the Higgs mode. Still, this example is unique among all known compounds. The student will explore a new family of compounds. Our goal is to discuss the universality of the detection of such mode. The student will perform symmetry dependent electronic Raman scattering experiment at low temperature and under high pressure on a chosen family of superconductors.

Possible collaboration and networking:

We already have a close theoretical collaboration with Lara Benfatto (ISC/Roma) on this topic. Collaboration with samples’ growers is also established. Networking: ANR project.

Possible extension as a PhD: YES. This study will be done in the context of an ANR project.

Required skills: knowledge of condensed matter physics, curiosity, taste for delicate experiments.

Starting date: march-april 2018

Contact: Name: Marie-Aude MéassonInstitut Néel - CNRS Phone: 06 26 44 72 33 e-mail: [email protected]

Fig. 2 : Raman spectra of NbSe2, a compound which presents a charge-density-wave (CDW) mode and may present a superconducting Higgs mode below Tc~7K, as observed by Raman spectroscopy.



82

Study of the physical properties of new unconventional bidimensional superconductors under extreme conditions of pressure

General Scope : The mechanism of high Tc superconductivity remains an open question in condensed matter physics. Such superconductors show record Tc values of 135K for Cu based families and 55K for iron based arsenides and chalcogenides at ambient pressure. The electron-phonon coupling is too weak in these layered materials to explain their high Tc, other mechanism such as spins fluctuations has to be involved. The comparison of the physical properties of the different families helps to find the relevant parameters to reach high Tc superconductivity. In that sense, the use of high pressure (HP) to explore their phase diagram is a good way to probe the physics of the parent and superconducting phases. We actually use this approach in our laboratory to study FeSe (see fig. 1a). Research topic and facilities available : More recently, we were interested in systems were Fe2Se2 unit blocks are separated by A2MO2 (Ae=Ba,Sr,Ca or K and M=Co or Cu) (see fig. 1b) because increasing distance between Fe planes favors higher Tc. By extension we try currently to synthesize pure Fe- or pure Cu-based layered systems with A2CuO2Cu2As2 and A2FeO2Fe2As2 compositions. An intermediate system, Ba2Ti2Fe2As4O, where Fe2As2 layers are separated by Ti2O sheets, is also interesting because it shows two coexisting states: superconductivity in Fe planes and a charge or spin-density wave in Ti based sheets. During the internship, we will focus on one of these systems to characterize its physical properties at ambient pressure and study how they change under extreme condition of pressure. In particular we will combine structural (by x-ray diffraction in a diamond anvil cell), phonons (by Raman spectroscopy) and transport measurements (in a diamond Bridgman anvil apparatus) under HP.

(a) (b) (c) Fig.1 : (a) Pressure temperature phase diagram of FeSe (V. Svitlyk et al. Phy. Rev. B 96, 014520 (2017)); (b) and (c): Crystallographic structures of (Ba,K)2CuO2Fe2As2 (Dai et al. Chin. Phys. B 25, 077402 (2016)) and Ba2Ti2Fe2As4O (Wu et al. Phys.RB 89, 134522 (2014)).

Possible collaboration and networking : Since the discovery of superconductivity in iron-based compounds, an important knowledge of this family has been developed in our laboratory. The candidate will benefit of it and will have the opportunity to interact with several collaborators at NEEL Institute but also outside from Grenoble. Possible extension as a PhD : Yes (via a selection organized by the Physics Graduate School). Required skills : The candidate must have a good background in solid state physics, crystallography and material science. In addition he has to be motivated by working with high pressure experimental setups requiring precision and skill. Starting date : April 2017. Contact : TOULEMONDE Pierre and NUNEZ-REGUEIRO Manuel Institut Néel - CNRS : 04 76 88 74 21, [email protected]; 04 76 88 78 38, [email protected] More information : http://neel.cnrs.fr



83

Search for new high critical temperature superconductors General Scope: Unconventional superconductivity with high critical temperature (Tc) occurs by doping in two-dimensional (2D) compounds presenting an antiferromagnetic order with a high Néel temperature (TN) and a low magnetic moment. This is linked to the strong exchange interaction, responsible for antiferromagnetism but also for superconductivity. In particular, this is the case for cuprates and iron-based chalcogenides or arsenides. Thus a reasonable strategy for finding new nonconventional superconductors with high Tc is to select materials with these properties, synthesize them and chemically dope them. In particular chromium compounds are known to have strong antiferromagnetism. Those with a low dimensionality are difficult to synthesize, which is an important obstacle, but also allows us to be among the first to study them to understand their physics. This can be very rich, regardless of whether or not superconductivity is obtained (Kondo Orbital effect in CrSe2 [M. Núñez et al. Phys. Rev. B. 88 (2013)]; Quantum fluctuations at 600 K in CrRe [D. Freitas et al. Phys. Rev. B. 92 (2015)]). Even if few years ago, thinking about finding superconductivity in chromium compounds made experts sceptical, its discovery in CrAs under pressure [Wu Wei et al. Nature Comm. 5 (2014)], now allows to expand this type of study.

Research topic and facilities available: Firstly, we propose first to try the doping of the Ruddlesden-Popper Æn+1CrnO3n+1 series (where Æ is an alkaline earth, see figure). We have already synthesized the parent phases n = 1, 2 and 3, and we have understood their physics, thanks to a collaborative work between experimentalists and theoreticians [Jeanneau et al. PRL 118 (2017)]. The synthesis of these oxides requires high pressure and high temperature conditions, which are available in the high-performance infrastructure of Institut Néel. The crystallographic, electrical and magnetic properties, as well as the specific heat and the thermal expansion will be probed thanks to the various experimental setups available in our laboratory. Measurements under very high pressure will complete the study. Secondly, depending on the scientific context in 2018, a second family, i.e. new 2D hydrogenated iron based-germanides or silicides where superconductivity has been discovered at Tc = 8K in LaFeSiH recently (arxiv/condmat:1701.05010), could be studied during the internship. Possible collaboration and networking: Measurements using neutron scattering (ILL) and/or X-rays on synchrotron (ESRF) will also be required in the medium term to understand the full set of properties. On the other hand, this subject will benefit from interactions with the theoreticians of the laboratory or from abroad. Possible extension as a PhD : Yes (via a selection organized by the Physics Graduate School). Required skills : A good knowledge of the physics of condensed matter is desired.Starting date : April 2017. Contact : TOULEMONDE Pierre and NUNEZ-REGUEIRO Manuel Institut Néel - CNRS : 04 76 88 74 21, [email protected]; 04 76 88 78 38, [email protected] More information : http://neel.cnrs.fr



84

Superconducting Josephson junctions based on Van der Waals Heterostructures

General Scope: 2D systems forms an emerging class of materials which recent progresses in nanotechnology allow to isolate and electrically connect down to a single monatomic layer . As they only consist of two surfaces and have no real “interior” (i.e. no bulk) they are extremely sensitive to their environment and their interface with other materials must be carefully monitored in order to measure their pristine properties. Such device allow to study a wealth of physical phenomena with unprecedented control. Research topic and facilities available This Master project focuses on the production and study of quantum electron transport properties of 2D materials devices for which the conducting monolayer (Graphene or a 2D semiconductor) is encapsulated in between two layers of an insulating material (hexagonal Boron Nitride, BN), before being side-contacted with lateral electrodes and gated with a set of top electrodes. Such a sandwich-like structures is realized by micromanipulation, stamping and stacking. Efficient and reliable stamping is taking advantage of the strong Van-der-Waals interactions that exist in between the ultraflat and flexible layers. High mobility BN/graphene/BN heterostructures will be patterned pads and connected to superconducting electrodes. Metal gates patterned on the top BN layer will act as local gates that

define the device electrostatic potential. A typical device structure is shown in figure 1. These experiments will involve high frequency electrical transport at ultra-low temperatures (<30mK) and magnetic fields up to 6T . Mastering the generally this project encompasses the full range of studies for the observation of electronic quantum properties and optoelectronic phenomena at the interface of 2D materials. The following setups are already operating: Glove box for assembly and encapsulation of air-sensitive materials, two motorized micromanipulation stages coupled to optical microscope equiped with digital camera, cryogenic Probe station for rapid testing of the electronic properties, two dilution

fridges that enable the measurement of the quantum electronic properties down to 30mK Possible collaboration and networking: The master student will work in close supervision with the team members including the PhD student who will transmit his know-how for the assembly of the structures. This work is supported by several ANR grants built on national collaborative projects on heterojunctions. Possible extension as a PhD: A PhD position will be open in the direct continuation of this internship. This subject is elligible to several grant applications. Required skills: This intership requires investiment in hands-on experiments. Strong interest in experimental nanotechnology is alsorequired. Starting date: March 1st, 2018 Contact: Name: Vincent Bouchiat Institut Néel - CNRS Phone: 04 56 38 70 74 e-mail: [email protected] More information: http://neel.cnrs.fr



85

Superfluidity of light dressed with excitons in nanostructured semiconductor microcavity

General Scope: Exciton-polaritons are quasi-particles of hybrid light and electron-hole pair (i.e. "exciton") nature. They are laboratory objects which exists only in semiconductor nanostructure designed for this purpose. Experimentally, they can be created and observed with a high degree of accuracy by rather simple optical means. Moreover, polaritonic structures benefits from - and triggered - progress in semiconductor nanotechnology : their spatial environment can thus be tailored at will with an exquisite level of precision : waveguides, lattices, traps, in which their properties can sometime be tuned in-situ. The most striking aspect of polaritons is the fact that they constitute a unique experimental realization of a nonequilibrium quantum fluids [1]. "Nonequilibrium" refers here to the fact that polaritons are in a driven-dissipative regime resembling the dynamics of a laser. This exotic situation leads to a wealth of new physics like e.g. the nonequilibrium counterparts of Bose-Einstein condensation and superfluidity [2]

Research topic and facilities available: In this project the candidate will participate in the ongoing experimental research focused on the superfluid state of exciton-polaritons. The aim of this research is to understand this state when polaritons are confined in low dimensional and periodic potential. Possible collaboration and networking: This project involves several collaboration, in particular : Drs. J. Bloch and A. Amo in C2N-CNRS, Paris ; profs C. Schneider and S. Hofling, Würzburg university, Germany.

Required skills: The candidate must have a very good track record in quantum optics, and/or optoelectronics properties of semiconductor nanostructures, and/or ultra-cold atom physics. He/She is to carry out quantum optics experiments. Some good understanding of the principle of optical spectroscopy is required. Participation in the data analysis, and theoretical treatment will be required. Extension as a PhD project is possible. Starting date: early 2018 Contact: Name: RICHARD Maxime Institut Néel - CNRS e-mail: [email protected] More information: http://neel.cnrs.fr [1] "Quantum fluids of light", I. Carusotto and C. Ciuti Rev. Mod. Phys. 85, 299 (2013) [2] On condensation and superfluidity : J. Kasprzak et al., Nature 443, 409 (2006) ; A. Amo et al., Nat Phys, 5,

805 (2009)

Figure (credit: [1]) - polaritons (grayscale) flowing in a plane against against an obstacle (centre black spot). TRansition from the normal (left panel) to superfluid (right panel) state.



86

Nanofils ferromagnétiques d’alliage à mémoire de forme Ni-Mn-X (x=In, Ga)

Cadre général : L’objectif de ce stage porte sur l’élaboration et la caractérisation de nano-filaments ferromagnétiques à mémoire de forme de type Ni-Mn-X (X=In, Ga). Ces matériaux, dans le cas des monocristaux, présentent des déformations pouvant atteindre 10% sous l’action d’un champ magnétique. Cependant, la déformation induite par le champ magnétique est réduite à néant pour les poly-cristaux de part les contraintes engendrées par les joints de grain. Les propriétés de couplage mécanique-magnétique et thermique sont donc particulièrement délicates à étudier. Le développement d’applications de type micro-actionneurs ou micro-capteurs basées sur l’obtention de couches minces se trouve également bloqué par le caractère multi-variantes et multi-grains des films élaborés.

Sujet exact, moyens disponibles : Nous proposons d’élaborer des nano-fils de quelques dizaines de nanomètres de diamètres qui permettront d’envisager une croissance unidimensionnelle limitant le nombre de joints de grain. La croissance de tels matériaux sous forme nanométrique n’a pour le moment jamais été réalisée et constituerait une réelle avancée pour le développement de microsystèmes mais aussi pour la compréhension de propriétés de couplage de ces nouveaux composés. Nous envisageons au cours de ce stage d’utiliser les membranes d’alumine nano-poreuse fabriquées par un procédé de double anodisation bien maitrisé par le laboratoire. La croissance des nano-fils ferromagnétiques à mémoire de forme de type Ni-Mn-X sera ensuite réalisée par dépôt électrochimique. Il s’agira de trouver les conditions de dépôt permettant un contrôle de la composition. Cette dernière ayant une forte influence sur la température de Curie et sur la température de transformation de phase Martensite-Austénite. Pour une application basée sur la déformation induite par le champ magnétique à la température ambiante, on cherchera à obtenir une température de transformation de phase supérieure à 300K. Des études de la microstructure par MEB-FEG et TEM ainsi que par diffraction X devront être réalisées en parallèle aux caractérisations des propriétés magnétiques (VSM-SQUID) et électriques %(T, H). Ce stage pourra se poursuivre par une thèse : oui Formation / Compétences : Physique et nanophysique, physique des matériaux et nanostructures, électrochimie. Le candidat devra avoir des bases solides en physique du solide et cristallographie ainsi qu’un goût prononcé pour l’expérimentation. Des connaissances en électrochimie seront tout particulièrement appréciées mais pas forcément nécessaires. Période envisagée pour le début du stage : février-mars 2018 Contact : Laurent CAGNON (1), Daniel BOURGAULT (2)

(1) Institut Néel – Département Nanosciences – Tél : 04 76 88 12 37 Mél : [email protected]

(2) Institut Néel – Département MCBT – Tél : 04 76 88 90 31 Mél : [email protected]

Plus d'information sur : http://neel.cnrs.fr

100nm

MET sur film Ni-Mn-Ga



87

TeraHertz waves generation from phase-matched difference frequency conversion in non linear crystals

General Scope: The scope of this internship is the implementation of a source emitting high power coherent Tera Hertz (THz) light that is tunable in the frequency range 100 GHz - 20 THz i.e. in the wavelength range 3000 µm - 15 µm. It is of prime importance for many applications as spectroscopy, biomedical imaging and telecommunications for example. The generation of THz light has been provided by antenna, Quantum Cascade Lasers (QCL) and the generation of parametric light. We selected this last technical solution that has the advantage to generate the most powerful and tunable Thz waves. Our experimental setup is under progress. It uses phase-matched difference frequency generation (DFG) between two wavelengths interacting collinearly in non linear crystals from a nonlinear quadratic process. Research topic and facilities available: [1] Optics Letter 38 (6) 2013. [2] Optics Express, 21(23) 2013.

We are using two incoming monochromatic beams emitted by two 5 nanosecond-pulsewidth and 10 Hz-repetition rate Optical parametric Oscillators (OPOs). The OPOs are identical, tunable between 1.4 "m and 4.4 "m.and synchronously pumped by the same pump beam. But their energy, wavelength and polarization are completely independent [1,2]. The internship will consist first in adding second harmonic generation (SHG) stages to convert the tunability range of the two OPOs between 0.7 "m and 2.2 "m, and in generating THz from phase-matched DFG in the selected non linear crystals.

The non linear crystals will be selected from the recording of their transmission spectra in polarized light. The possible value of the generated THz wavelength that is directly linked to that of the two incoming vavelengths (i.e. by energy conservation), will be limited by the THz transparency range of the nonlinear crystals. The samples will be cut as slabs oriented in order to take advantage of their highest nonlinear coefficient and to generate THz from DFG under phase-matching conditions. The determination of these data is provided by a unique method we implemented several years ago in our research team. Possible collaboration and networking : Collaboration with IMEP-LAHC (Chambéry), Tera-photonics laboratory, RIKEN Sendai in Japan, and State Key Laboratory of Crystal Materials and Institute of Crystal Materials, Shandong University, Jinan in China. Starting date: starting from february or march 2018 Possible extension as a PhD: Yes Required skills: A background in laser optics and non-linear optics will be appreciated. Contacts: Patricia Segonds ([email protected]) and Benoit Boulanger ([email protected]) Institut Néel CNRS : tél 0476887807. For more information : http://neel.cnrs.fr



88

Probing the superfluid density in dichalcogenides superconductors General Scope: Superconductivity is a macroscopic manifestation of the quantum coherence of electrons. The ability to probe the superfluid condensate is a key step to understand the mechanisms responsible for superconductivity. Very successful models have allowed a deep understanding of these mechanisms in pure compounds and many alloys. But the debate is completely open about the origin of superconductivity in materials with strong electronic correlations which can induce different kind of ground states. Consequently, in these systems, the link between the different electronic phases has to be clarified. The use of an external parameter such as pressure or the thickness of the sample can allow us to tune the ground state and modify the different energies scales. Among different systems, the transition metal dichalcogenides are very promising.

Research topic and facilities available: We will probe the superconducting properties by measuring simultaneity the magnetic penetration depth λ and the thermodynamic field associated : the lower critical field. This is very fundamental and directly related to the electron density forming the superfluid condensate but also to the superconducting gap. Moreover, the temperature dependence reflects the existence of possible nodes in the superconducting gap, a consequence of broken symmetry induced in the superconducting state. We will compare the results obtained to different models.

Possible collaboration and networking: We will use an original experimental set-up with world wide performances. We will work at very low temperature very close to the absolute 0K. The candidate will have the opportunity to interact with several collaborators at Neel institute and out the laboratory. Possible extension as a PhD: Yes Required skills: The candidate will have a strong background in solid state physics, electromagnetism and quantum mechanics. Starting date: Contact: Name: Rodière Pierre Institut Néel - CNRS Phone: +33 (0)4 76 88 10 26 e-mail: [email protected] More information: http://neel.cnrs.fr

Different kind of layer of dichalcogenides.



89

Investigation of magnetization processes in R-M intermetallic compounds General scope : The R-M phases based on rare-earth (R) and transition metals (M) are fascinating materials from both applied and fundamental viewpoints. Indeed, R-M have led to the first modern magnets like Sm-Co (SmCo5 and Sm2Co17 type) and latter to the high performance Nd-Fe-B magnets. Other examples are the (Dy,Tb)Fe2 type Terfenol ® alloys which are by far the best magnetostrictive materials to date and are widely used in sensors and actuators leading to many applications (Sonar). Other R-M alloys have also contributed to the development of various techniques such as magneto-optic recording on thin films (Gd-Co). Some compounds are now also considered for new applications such as spintronic devices (Gd-Co), magnetic refrigeration using magnetocaloric materials (LaFeSi, RCo2..). The R-M compounds are however complex materials and need fundamental studies to master their magnetic properties and optimize their performances. Indeed, they are combining two types of magnetism, the localized magnetic moment originating from the inner 4f electronic shells of the R element with the delocalized magnetic moments carried by the itinerant 3d electrons of the M transition metals. Depending upon the atomic concentration one can thus play with different origin of the magnetization. From a fundamental point of view, the R-M compounds are ideal systems to probe solid state magnetism since they are presenting a wide range of unusual magnetic behaviour. Research to be carried out : Among the interesting magnetization process that attracted our attention, we can cite magnetization reversal in hard magnetic materials exhibiting promising magnetic properties for permanent magnet applications. We also recently discovered the occurence of ultrasharp magnetization behaviour in LaFe12B6 see Figure. This manifest itself by unexpected giant metamagnetic transitions consisting of a succession of extremely sharp magnetization steps separated by plateaus. This behavior has been found at low temperature in LaFe12B6. This unprecedent behaviour for a purely 3d itinerant electron system needs to be further investigated since it presents many remarkable properties. For instance, under certain combinations of the external parameters (temperature and magnetic field), the time dependence of the magnetization displays an unusual step-like feature. However, the origin

and the underlying mechanism involved in such unusual magnetization process have to be clarified. The internship will include synthesis of polycrystalline samples, measurements of their physical properties (structural and magnetic) and analysis of the observed behavior. This will be done in close interaction with the researchers using equipments already available.

Ongoing collaborations : In the frame of this research work, different collaborations are already established in particular with the Institute Laue Langevin, as well as Czech collaborators specialists of magnetic measurements at high pressure. This will be an added value to the project. This internship is aimed to be followed by a Ph. Thesis Formation / skills : Master 2 in Solid State Physics or Nanophysics or Engineer in Materials sciences Starting period foreseen : February or march 2018 Contact : Pr. Olivier ISNARD, Département PLUM Institut Néel - CNRS : tél 04 76 88 11 46 email [email protected] see also : http://neel.cnrs.fr

-‐10 -‐8 -‐6 -‐4 -‐2 0 2 4 6 8 10-‐20

-‐15

-‐10

-‐5

0

5

10

15

20

M (µ

B/f.

u.)

µ0H (T)

LaFe12B6

2 K

C

D

A

E

B



90

From engineering a half-open Floquet qu-bit to thermodynamics of topological effects in multi-terminal Josephson junctions

General Scope: Many experimental and theoretical works in the field of quantum nanoelectronics aim at manipulating simple systems with small numbers of degrees of freedom. Several implementations have been realized, on the basis of Josephson junctions. Those qu-bits are the building block of the complex architectures used to realize a quantum computer. The phase drop phi across a two-terminal Josephson junction is linear as a function of time : dphi/dt=2eV/hbar, where V is the bias voltage. Voltage biasing a superconductor-quantum dot superconductor Josephson junction produces a driven two-level system with time-periodic Hamiltonian in the limit where the superconducting gap is much larger than all other energy scales. Thus, the description becomes especially simple in this limit of infinite gap. Two theoretical proposals have been made recently, which aim at using a Josephson junction as a simulator of some effects appearing in band theory. Superconducting phase variable between 0 and 2pi plays the role of wave-vector in the Brillouin zone : 1. The first proposal in our group consists in using a three-terminal Josephson junction in order to simulate the wave-function of an electron in the presence of electric field, and in a periodic potential. The time periodicity of the Josephson Hamiltonian plays the role of the potential of the crystal lattice, which is periodic in space. The physics is then related to Bloch oscillations and to Wannier-Stark resonances. It is possible to fabricate on this basis a two-level system in Floquet space, namely, a qu-bit sharing some features of open systems, and others of closed systems. 2. The second proposal by Nazarov and co-workers consists in using a four-terminal Josephson junction in order to produce nontrivial topology analogous to conductance quantization in the integer quantum Hall effect. The goal of the interrnship is to carry out semi-classics in one of the simplest situations, in order to interpret available numerical data. The goal of the PhD thesis is to propose a scheme allowing to optimize coherence time using backaction, to develop a quantum thermodynamics viewpoint, to develop analytical calculations based on semi-classics and to account for interactions. Collaborations are with Benoît Douçot (Jussieu, Paris), with the group of mathematical physics of Institut Fourier (Alain Joye and Frédéric Faure), and with Jean-Guy Caputo (applied mathematics). Required skills: The candidate should either be motivated by numerical calculations or by more theoretical developments, or by both. Starting date : Anytime during academic year 2017-2018. Contact: Dr. Régis Mélin, Institut Néel-CNRS, Grenoble, e-mail : [email protected] Phone: 04-76-88-11-88. Web site : http://perso.neel.cnrs.fr/regis.melin/ More information : A ten pages detailed project is available upon request

NOTES

NOTES

Documents

4V+'*>,1(=% - Institut Néelneel.cnrs.fr/IMG/pdf/Brochure_2017-2018_WEB.pdf · 11 INSTITUT NEEL Grenoble Proposition de stage Master 1 - Année universitaire 2017-2018 Dilatation