WorldCat Identities

Simon, Pascal (1970-....; physicien)

Overview
Works: 22 works in 25 publications in 2 languages and 31 library holdings
Roles: Opponent, Other, Thesis advisor, Author
Publication Timeline
.
Most widely held works by Pascal Simon
LES PREMIERS SEMICONDUCTEURS MOLECULAIRES : LES DERIVES RADICALAIRES DES PHTALOCYANINES by Raymond Even( Book )

2 editions published in 1987 in French and held by 4 WorldCat member libraries worldwide

SYNTHESE DE COMPOSES PC::(2)LU, PC::(2)LN(LN = YB,TM,DY,ND) A L'ETAT DE GRANDE PURETE ET ETUDE DE LEURS PROPRIETES ELECTRIQUES INTRINSEQUES, AINSI QUE DE CELLES DE PCLI, SUR MONOCRISTAUX ET SUR COUCHES MINCES; MISE EN EVIDENCE DE LA POSSIBILITE DE DOPAGE DE PC::(2)LU AVEC DES COMPOSES ORGANIQUES DONNEURS ET ACCEPTEURS ET AVEC PCLI. ETUDE DE L'ABSORPTION OPTIQUE ET OBSERVATION DE BANDES DE TRANSFERT DE CHARGE INTRAMOLECULAIRE, CONFIRMEE PAR AILLEURS PAR RPE. POSSIBILITE D'APPLICATION DE COUCHES MINCES DE PCLU A LA DETECTION DE GAZ
DES SYSTEMES BIDIMENSIONNELS FRUSTRES AUX MODELES MINIMAUX COUPLES by Pascal Simon( Book )

2 editions published in 1998 in French and held by 3 WorldCat member libraries worldwide

LA PREMIERE PARTIE DE CETTE THESE EST CONSACREE A L'ETUDE D'UN MODELE XY, 2D FRUSTRE PAR DES INTERACTIONS COMPETITIVES. NOUS MONTRONS QUE LE DIAGRAMME DE PHASE DE CE MODELE POSSEDE DEUX REGIMES DIFFERENTS, UN REGIME FAIBLEMENT FRUSTRE, DANS LEQUEL LA TRANSITION EST DE TYPE XY NON-FRUSTRE, ET UN REGIME FORTEMENT FRUSTRE, DANS LEQUEL LA SYMETRIE EST DE TYPE Z(2) U(1). NOUS FAISONS UN BILAN DES PRINCIPAUX TRAVAUX SUR LES MODELES AVEC DES SYMETRIES SIMILAIRES ET DONNONS UN SCENARIO PLAUSIBLE POUVANT EXPLIQUER LE COMPORTEMENT CRITIQUE. DANS LA PARTIE II, NOUS ANALYSONS LES EFFETS DES FLUCTUATIONS THERMIQUES ET QUANTIQUES SUR UN MODELE FORTEMENT FRUSTRE : LE MODELE DE HEISENBERG ANTIFERROMAGNETIQUE SUR LE CACTUS DE HUSIMI. CE MODELE EST UNE SIMPLICATION DE SYSTEMES REALISABLES EXPERIMENTALEMENT COMME LES RESEAUX PYROCHLORE ET KAGOME. NOUS AVONS MONTRE QUE LES FLUCTUATIONS THERMIQUES LAISSENT INVARIANT LA DEGENERESCENCE CLASSIQUE CONTRAIREMENT AUX FLUCTUATIONS QUANTIQUES QUI SELECTIONNENT UN NOMBRE DISCRET D'ETATS FONDAMENTAUX. FINALEMENT, DANS LA PARTIE III, NOUS APPLIQUONS LES METHODES DE THEORIE CONFORME POUR ETUDIER DES MODELES CRITIQUES COUPLES, RELIES AUX THEORIES Z(2) U(1) INTRODUIT DANS LA PARTIE I. NOUS AVONS GENERALISE CETTE ANALYSE EN PRESENCE DE DESORDRE. PLUS PRECISEMENT, NOUS AVONS OBTENU LES FLOTS DE RENORMALISATION POUR DES MODELES DE POTTS A Q ETATS COUPLES (N SYSTEMES A Q = Q#1 COUPLES A M SYSTEMES A Q = Q#2), EN UTILISANT UNE EXPANSION EN = Q 2. NOUS AVONS OBTENU UNE RICHE VARIETE DE FLOTS. POUR M = 1, ET N 2, DE NOUVEAUX POINTS TRICRITIQUES ONT ETE OBTENU SUSCEPTIBLES D'EXPLIQUER CERTAINES DONNEES NUMERIQUES SUR LA THEORIE Z(2) U(1)
Effet Kondo dans une géométrie triterminale by Julien Salomez( Book )

2 editions published in 2006 in French and held by 2 WorldCat member libraries worldwide

In this manuscript, we are interested in a quantum dot connected to three reservoirs. The Kondo cloud essentially develops in the third reservoir which is strongly coupled to the quantum dot. The other two reservoirs are weakly coupled to the quantum dot and are used to probe the system by transport measurements. After modeling such a three-terminal geometry, we have calculated the conductance matrix at zero temperature by Fermi liquids theory. In the remaining of the manuscript, we focus on the case where the third reservoir has a finite size, which confers to its density of state a peaks structure. We have first studied the system by the perturbative renormalisation group and have evaluated the Kondo temperature, which is the main energy scale of the problem. Next, we have calculated the conductance matrix of the system at different temperatures. For temperatures much stronger than the Kondo temperature, we have used a perturbative approach. For temperatures much weaker than the Kondo temperature, we have used a Fermi liquid type theory. In the intermediate regime, we have used a numerical method called slave bosons mean field theory. In the latter regime, we have also performed a spectroscopic analysis of the dot density of states
Quantum coherent phenomena in disordered transition metal dichalcogenide monolayers by Stefan Ilic( )

1 edition published in 2019 in English and held by 2 WorldCat member libraries worldwide

Les monocouches de dichalcogénures de métaux de transition (TMDC) sont des matériaux bidimensionnels découverts récemment. Ils possèdent un fort couplage spin-orbite (SOC) intrinsèque qui agit comme un champ Zeeman effectif perpendiculaire, mais avec des orientations opposées dans chaque vallée située autour des points +K et -K de la zone Brillouin. En présence de désordre, ce SOC influence fortement les phénomènes quantiques cohérents dans les TMDC. Dans cette thèse, nous étudions deux de ces phénomènes : la supraconductivité et les corrections à la conductance dues aux interférences quantiques, telles que la localisation ou l'anti-localisation faible, ainsi que les fluctuations universelles de la conductance.Une supraconductivité a été identifiée expérimentalement dans plusieurs TMDC, aussi bien dans les régimes dopés n (MoS2, WS2) que p (NbSe2, TaS2). Dans ces matériaux, le SOC intrinsèque provoque un "appariement d'Ising" inhabituel des paires de Cooper. En effet, celles-ci sont formées avec des électrons provenant de vallées opposées, donc leurs spins sont figés perpendiculairement à la couche. Un champ magnétique appliqué parallèlement à la couche n'est donc pas efficace pour briser les paires de Cooper par l'effet paramagnétique, ce qui entraîne une augmentation considérable du champ critique dans le plan. C'est la signature principale de la supraconductivité d'Ising. Dans la première partie de ce travail, nous calculons le champ critique et la densité des états dans les TMDC supraconducteurs désordonnés. Nous montrons que la diffusion intra-vallée n'affecte pas ces propriétés. En revanche, elles dépendent fortement de la diffusion inter-vallée qui produit un mécanisme de brisure des paires de Cooper. Dans les supraconducteurs Ising dopés p, dans lesquels plusieurs bandes croisent le niveau de Fermi, nous identifions la diffusion inter-bande comme un autre mécanisme important de brisure des paires. Nous montrons qu'une faible diffusion inter-vallée ou inter-bande peut expliquer les observations expérimentales dans les supraconducteurs TMDC dopés n ou p, respectivement.Dans la deuxième partie de ce travail, nous calculons les corrections à la conductance dues aux interférences quantiques dans les TMDC métalliques. Leur mesure peut servir de sonde indépendante pour identifier la nature du SOC et du désordre. En raison de l'interaction entre la structure de la vallée et le SOC, ces matériaux présentent un riche comportement de localisation (ou anti-localisation) faible et des fluctuations universelles de la conductance, qui sont qualitativement différents des autres systèmes bidimensionnels, comme les métaux conventionnels ou le graphène. Nos résultats peuvent également être utilisés pour décrire les hétéro-structures graphène/TMDC, dans lesquelles le SOC est induit dans la couche de graphène. Nous discutons différents régimes de paramètres qui permettent d'interpréter des expériences récentes et d'évaluer l'intensité du SOC et du désordre. En outre, nous montrons qu'un champ Zeeman dans le plan peut être utilisé pour distinguer les contributions de différents types de SOC à la localisation ou l'anti-localisation faible
Yu-Shiba-Rusinov bound states versus topological edge states in Pb/Si(111) by Gerbold C Ménard( )

1 edition published in 2019 in English and held by 2 WorldCat member libraries worldwide

Supraconductivité et localisation dans des nanofils unidimensionnels d'InSb et d'InAs by Juan Carlos Estrada Saldaña( )

1 edition published in 2017 in English and held by 2 WorldCat member libraries worldwide

In my thesis, I studied low-temperature electronic transport in semiconductor nanowires coupled to superconductors, with the goal of understanding the requirements to observe Majorana bound states. Unexpectedly, I found dramatic examples of the pervasiveness of spatial localization of electrons even in seemingly ballistic one-dimensional (1D) nanowires. Localization could replicate signatures of one-dimensionality, helicity and Majorana bound states, casting a shadow of doubt on their interpretation.1D nanowires are expected to show plateaus of quantized conductance. Curiously, transport through an InAs nanowire hosting a single-level quantum dot showed that it could mimic the first two spin-resolved plateaus. A measurement of the Josephson supercurrent under magnetic field revealed the ground-state transitions of an electron occupying this level, confirming its localized nature.In the helical regime, a conductance dip is predicted to appear in each of the conductance plateaus. Surprisingly, InSb nanowire devices hosting a quantum dot conducting in parallel with a 1D channel reproduced this signature.The presence of Majorana bound states, in turn, should be revealed by a zero-bias peak (ZBP) in tunnel spectroscopy. In one of the two-path devices mentioned above, when the 1D path was closed, a zero-bias peak emerged inside the superconducting gap under a magnetic field parallel to the nanowire. This ZBP was related to trivial Andreev bound states from the quantum dot in parallel to the 1D channel. In a different experiment done in an InAs nanowire Josephson junction device hosting a quantum dot, a ZBP related to a Josephson supercurrent appeared inside of the superconducting gap as a result of a transition of the ground-state of the dot from a singlet to a doublet.In spite of localization, it was possible to extract some meaningful information about the 1D regime. The role of the gates was major in determining the degeneracy of the subbands in an InSb nanowire with two 1D conduction paths in parallel under magnetic field. Through a direct influence on their threshold voltages, orbital effects, and g-factors, the gate voltage could shift the energies of the subbands and lock them together. Via this mechanism, it was possible to observe a 2e^2/h plateau lasting until very large field without the appearance of a 1e^2/h plateau. The possible existence of two quantum wires in a single nanowire opens the door for novel helical and Majorana bound states of fractional nature.Altogether, these results point to the need of a better understanding of the physics of simpler few-gates short-channel InAs and InSb nanowire superconducting and normal-state devices, before committing to the utterly complex devices that should be fabricated to study and manipulate Majorana bound states, in which signatures of localization could be better hidden. These original results will be published in the coming months in four different articles
Time-resolved quantum nanoelectronics in electromagnetic environments by Benoît Rossignol( )

1 edition published in 2020 in English and held by 1 WorldCat member library worldwide

Quantum nanoelectronics is in a phase of great expansion, supported mainlyby the development of quantum computing. A high degree of precision isrequired to achieve current objectives, but on the other hand, the experi-ences are also more complex than ever. Nuremical tools seem necessary toachieve the required understanding while dealing with such complexity. Thetime scales involved are getting shorter and are getting closer to the intrinsicquantum time scales of the device, such as time of flight. Our group's pre-vious work has simulated time-dependent electron transport on a quantumscale. This thesis aims to improve the previous algorithms to obtain greateraccuracy and a better description of the systems by including the electronicenvironment. This work is divided into three main areas. First, we improveof numerical time-dependent simulation tools to take into account an elec-tronic environment in a self-consistent way. The new algorithm can achievearbitrary accuracy in a controlled way. Second, the new algorithm is used todemonstrate the existence of new physical phenomena. We study Josephsonjunctions in different environments to enhance the role of quasi-particles, theeffect of a very short pulse, and to study topological junction characteriza-tion techniques. Finally, various developments are being studied to integratethe phenomenon of decoherence and quantum noise into the simulations
Transport and spectral properties of low-dimensional superconductors in the presence of spin-dependent fields by Julie Baumard( )

1 edition published in 2019 in English and held by 1 WorldCat member library worldwide

The interplay between superconductivity and spin-dependent fields is known to lead to striking phenomena, like critical field enhancement, magnetoelectric effects and the appearance of Yu-Shiba-Rusinov bound states at magnetic impurities. In this thesis, we investigate these effects in low dimensional systems.We first demonstrate that the combination of both spin-orbit and Zeeman fields in superconducting one-dimensional systems leads to the appearance of an inhomogeneous phase at low magnetic field and high critical temperature. We show that the ground state corresponds to a zero-current state where the current stemming from spin-orbit coupling, called anomalous charge current, is exactly compensated by the current coming from the wave-vector of the superconducting order parameter. We also discuss how it is possible to predict the appearance of the anomalous current from symmetry arguments based on the SU(2)-covariant formalism.In a second part, we consider a type-II superconducting thin film in contact with a Néel skyrmion. The skyrmion induces spontaneous currents in the superconducting layer, which under the right condition generate a superconducting vortex in the absence of external magnetic fields. We compute the magnetic field and current distributions in the superconducting layer in the presence of the Néel skyrmion.In the last part of this thesis, we focus on the appearance of Yu-Shiba-Rusinov states in the superconducting crystal beta-Bi2Pd. We propose effective models in order to explain recent experimental results showing a double spatial oscillation of the local density of states at Shiba energy. We demonstrate that the minimal condition to reproduce this double oscillation is the presence of two superconducting channels connected via a hopping term or via a magnetic impurity. These effective models can be easily generalized to describe the spectrum of multiband superconductors with magnetic impurities
Josephson effect and high frequency emission in a carbon nanotube in the Kondo regime by Raphaëlle Delagrange( )

1 edition published in 2016 in English and held by 1 WorldCat member library worldwide

Edge states in Chern Insulators and Majorana fermions in topological superconductors by Doru Sticlet( )

1 edition published in 2012 in English and held by 1 WorldCat member library worldwide

De l'impureté Kondo aux états liés dans les supraconducteurs by Sébastien Guissart( )

1 edition published in 2016 in French and held by 1 WorldCat member library worldwide

In this thesis, I was mainly interested in the effects related to magnetic impurities in metals and superconductors.In the first chapter I will present the Kondo effect, this effect occurs when a magnetic impurity exhibits an antiferromagnetic coupling with the metal that it pollutes. The electrons then form, at a sufficiently low temperature, a cloud screening the magnetism of the impurity. The second chapter will focus on the states of Yu-Shiba-Rusinov products by magnetic impurities in a superconductor. In this case, the impurity locally breaks the superconducting order and a quantum state is created inside the gap.Some so-called topological materials may include quantum states protected at their edges against external perturbations. In the last two chapters, I will present the properties of topological superconductors and their edge states. In the third chapter I will present the different topological phases that can include a superconductor with a parameter of complex order mixing waves p and s in the presence of a Zeeman field.In the fourth and last chapter I will present a study of the states of edge that may include this type of superconductors
Collective localization transitions in interacting disordered and quasiperiodic Bose superfluids by Samuel Lellouch( )

1 edition published in 2014 in English and held by 1 WorldCat member library worldwide

In this thesis, we theoretically investigate the collective localization properties of weakly-Interacting Bose superfluids subjected to disordered or quasiperiodic potentials. While disorder has been recognized since Anderson to induce single-Particle localization, the interplay between disorder and interactions in quantum systems is today among the most challenging questions in the field, and underlies fascinating phase transitions and non-Trivial localization effetcs. Focusing on Bose gases in the weakly-Interacting regime for which the Bogoliubov theory proves a successful tool, we study the localization transitions of collective excitations in several contexts. First, in the case of a continuous true disorder, we develop a strong-Disorder formalism going beyond previous studies, providing us with a complete description of the localization behaviour of collective excitations in arbitrary dimension. A generic localization diagram is obtained and the transport of excitations in the disorder is microscopically interpreted. Secondly, we consider the case of one-Dimensional quasiperiodic potentials, which are known to display intermediate properties between periodic and disordered ones. We perform a numerical and analytical treatment of the localization problem of collective excitations, allowing us to quantitatively characterize and interpret the localization transition in terms of an effective multiharmonic problem. Finally, we set up the general inhomogeneous formalism to address such issues in multicomponent Bose gases, and enlighten the basic physic of such systems, which are known to exhibit their own specific features
Yu-Shiba-Rusinov states in superconductor-quantum dot transistors made by electromigration by Alvaro Garcia Corral( )

1 edition published in 2020 in English and held by 1 WorldCat member library worldwide

Une impureté magnétique intégrée dans un supraconducteur (SC) peut avoir un effet perturbateur sur la supraconductivité, réduisant localement l'énergie d'appariement des paires de Cooper et conduisant à la génération d'états sous-gap Yu-Shiba-Rusinov (YSR) autour d'elle.L'interaction d'échange entre le spin à l'impureté et les électrons au milieu favorise une configuration de singulet d'écrantage Kondo, tandis que les corrélations supraconductrices s'opposent à la formation d'un nuage d'écrantage, laissant l'impureté non-écrantée à l'état de doublet. L'état fondamental local (GS) du système est ensuite déterminé par l'interaction complexe entre les deux phénomènes, donnant lieu à des propriétés intrigantes qui ont fait l'objet d'un grand intérêt au cours de la dernière décennie.Les dispositifs hybrides mettant en contact des structures à boîte quantique (QD) avec des bornes supraconductrices offrent une plateforme idéale pour l'étude d'une telle concurrence, car les QD peuvent également montrer un caractère magnétique pour les occupations impaires. Dans cette thèse, nous étudions les propriétés de transport des QD colloïdaux (nanoparticules métalliques et fullerènes) mis en contact individuellement avec des bornes d'aluminium nues à travers des barrières tunnel faites par électromigration, dans une configuration de transistor. La combinaison d'une densité d'états fortement discrétisée dans des QD colloïdaux avec à net gap présent dans l'aluminium supraconducteur permet de mesurer les spectres YSR, apparaissant dans des jonctions SC-QD-SC affichant une grande asymétrie dans le couplage tunnel, avec une résolution sans précédent. La réponse du système SC-QD versus la tension de grille, le champ magnétique externe et la température a été caractérisée, identifiant le point de transition (QPT) dès la phase singulet-GS au doublet-GS. Une reprise frappante de la position du QPT est révélée à de faibles champs magnétiques, attribuée à la séparation Zeeman de l'état du doublet
Quantum transport in a correlated nanostructure coupled to a microwave cavity by Olesia Dmytruk( )

1 edition published in 2016 in English and held by 1 WorldCat member library worldwide

In this thesis, we study theoretically various physical properties of nanostructures that are coupledto microwave cavities. Cavity quantum electrodynamics (QED) with a quantum dot has been proven to be a powerful experimental technique that allows to study the latter by photonic measurements in addition to electronic transport measurements. In this thesis, we propose to use the cavity microwave field to extract additional information on the properties of quantum conductors: optical transmission coefficient gives direct access to electronic susceptibilities of these quantum conductors. We apply this general framework to different mesoscopic systems coupled to a superconducting microwave cavity, such as a tunnel junction, a quantum dot coupled to the leads, a topological wire and a superconducting ring. Cavity QED can be used to probe the finite frequency admittance of the quantum dot coupled to the microwave cavity via photonic measurements. Concerning the topological wire, we found that the cavity allows for determining the topological phase transition, the emergence of Majorana fermions, and also the parity of the ground state. For the superconducting ring, we propose to study the Josephson effect and the transition from the latter to the fractional Josephson effect, which is associated with the emergence of the Majorana fermions in the system, via the optical response of the cavity. The proposed framework allows to probe a broad range of nanostructures, including quantum dots and topological superconductors, in a non-invasive manner. Furthermore, it gives new information on the properties of these quantum conductors, which was not available in transport experiments
High frequency quantum noise of mesoscopic systems and current-phase relation of hybrid junctions by Julien Basset( )

1 edition published in 2011 in English and held by 1 WorldCat member library worldwide

Out-of-equilibrium dynamics in a quantum impurity model by Kemal Bidzhiev( )

1 edition published in 2019 in English and held by 1 WorldCat member library worldwide

Le domaine des problèmes quantiques à N-corps à l'équilibre et hors d'équilibre sont des sujets majeurs de la Physique et de la Physique de la matière condensée en particulier. Les propriétés d'équilibre de nombreux systèmes unidimensionnels en interaction sont bien comprises d'un point de vue théorique, des chaînes de spins aux théories quantiques des champs dans le continue. Ces progrès ont été rendus possibles par le développement de nombreuses techniques puissantes, comme, par exemple, l'ansatz de Bethe, le groupe de renormalisation, la bosonisation, les états produits de matrices ou la théorie des champs invariante conforme. Même si les propriétés à l'équilibre de nombreux modèles soient connues, ceci n'est en général pas suffisant pour décrire leurs comportements hors d'équilibre, et ces derniers restent moins explorés et beaucoup moins bien compris. Les modèles d'impuretés quantiques représentent certains des modèles à N-corps les plus simples. Mais malgré leur apparente simplicité ils peuvent capturer plusieurs phénomènes expérimentaux importants, de l'effet Kondo dans les métaux aux propriétés de transports dans les nanostructures, comme les points quantiques. Dans ce travail nous considérons un modèle d'impureté appelé "modèle de niveau résonnant en interaction" (IRLM). Ce modèle décrit des fermions sans spin se propageant dans deux fils semi-infinis qui sont couplés à un niveau résonant -- appelé point ou impureté quantique -- via un terme de saut et une répulsion Coulombienne. Nous nous intéressons aux situations hors d'équilibre où un courant de particules s'écoule à travers le point quantique, et étudions les propriétés de transport telles que le courant stationnaire (en fonction du voltage), la conductance différentielle, le courant réfléchi, le bruit du courant ou encore l'entropie d'intrication. Nous réalisons des simulations numériques de la dynamique du modèle avec la méthode du groupe de renormalisation de la matrice densité dépendent du temps (tDMRG), qui est basée sur une description des fonctions d'onde en terme d'états produits de matrices. Nous obtenons des résultats de grande précision concernant les courbes courant-voltage ou bruit-voltage de l'IRLM, dans un grand domaine de paramètres du modèle (voltage, force de l'interaction, amplitude de saut vers le dot, etc.). Ces résultats numériques sont analysés à la lumière de résultats exacts de théorie des champs hors d'équilibre qui ont été obtenus pour un modèle similaire à l'IRLM, le modèle de Sine-Gordon avec bord (BSG). Cette analyse est en particulier basée sur l'identification d'une échelle d'énergie Kondo et d'exposants décrivant les régimes de petit et grand voltage. Aux deux points particuliers où les modèles sont connus comme étant équivalents, nos résultats sont en accord parfait avec la solution exacte. En dehors de ces deux points particuliers nous trouvons que les courbes de transport de l'IRLM et du modèle BSG demeurent très proches, ce qui était inattendu et qui reste dans une certaine mesure inexpliqué
Spin polarisation and topological properties of Yu-Shiba-Rusinov states by Vardan Kaladzhyan( )

1 edition published in 2017 in English and held by 1 WorldCat member library worldwide

In this manuscript we first revisit the physics of Yu-Shiba-Rusinov subgap states, focusing on their spin polarisation. We start by showing theoretically that we can extract a considerable amount of information about the host superconductor, by analysing spin-polarised local density of states related to the presence of magnetic impurities. First, we demonstrate that the spin-orbit coupling in two-dimensional and one-dimensional systems, both superconducting and metallic, can be read-off directly and unambiguously via spin-resolved STM. We analyse the impurity-induced oscillations in the local density of states. In particular, we focus on the Fourier transform (FT) of the Friedel oscillations and we note that high-intensity FT features appear at a wave vector given by twice the inverse spin-orbit length. Second, in unconventional superconductors with both s-wave and p-wave pairing, by analysing the spin-resolved spectral structure of the Yu-Shiba-Rusinov states it is possible to determine the dominating pairing mechanism. Most strikingly, we demonstrate that a careful analysis of spin-polarised density of states allows not only to unambiguously characterise the degree of triplet pairing, but also to define the orientation of the triplet pairing vector, also known as the d-vector.Finally, we discuss two different ways of engineering and controlling topological phases with both scalar and magnetic impurities. We start with providing a microscopic theory of scalar impurity structures on chiral superconductors. We show that given a non-trivial chiral superconductor, the scalar impurities give rise to a complex hierarchy of distinct non-trivial phases with high Chern numbers. Second, we propose and study theoretically a new promising platform that we call 'dynamical Shiba chain', i.e. a chain of classical magnetic impurities in an s-wave superconductor with precessing spins. We have shown that it can be employed not only for engineering a topological superconducting phase, but most remarkably for controlling topological phase transitions by means of magnetisation texture dynamics.This manuscript is organised as follows. In the first part, the essential introductory information on superconductivity, Friedel oscillations and Yu-Shiba-Rusinov states is provided. The second part is dedicated to spin polarisation of Yu-Shiba-Rusinov states and the properties that could be extracted by means of spin-resolved STM measurements. In the last part, two setups proposed for topological phase engineering based on impurity-induced states are presented, followed by conclusions with a brief summary of the thesis achievements and further directions to pursue
Gaz bidimensionnels désordonnés : diffusion et transition superfluide by Baptiste Allard( )

1 edition published in 2012 in French and held by 1 WorldCat member library worldwide

This manuscript shows an experimental study of a disordered ultra-cold 87Rb gas confined in two dimensions.In the first part, we set up the experimental tools used to manipulate the confined gases. After a state of the art in ultracold 2D Bose gases, we describe our disorder-free experiment from which, by a comparison with quantum Monte-Carlo calculations and thanks to an accurate time-of-flight thermometry, we are able to quantify the emergence of coherence around the Berezinskii-Kosterlitz-Thouless superfluid phase transition. The second part is devoted to the effect of a micrometer-range optically generated disordered potential on the transport and coherence properties of the interacting 2D gas. This part follows the experimental road from the regime of classical transport, in which we have measured the energy dependence of the classical diffusion coefficient, to the regime of quantum transport we have just reached thanks to a last cooling step. On the road between those two regimes, we observe a shift towards lower entropy of the emergence of coherence close to the BKT transition as a response of an adiabatic addition of a moderate amount of disorder. It is strongly suppressed for an amount of disorder of the order of the cloud temperature. This work is a first step to an experimental study of the quantum transition to the Bose-Glass phase involving disorder and interaction
Phases désordonnées dans des gaz d'atomes froids de basse dimensionnalité by François Crépin( )

1 edition published in 2011 in French and held by 1 WorldCat member library worldwide

In this thesis we study two distinct problems related to the physics of quantum gases in one dimension. After writing a low-energy Hamiltonian, we address the question of localization by considering the pinning of density waves by weak disorder. Using the Renormalization Group and a variationnal method in replica space, we find that the phase diagram is adequately plotted as a function of two parameters: the strength of Bose-Bose and Bose-Fermi interactions. The position and properties of the various phases depend on an additional third parameter, the ratio of the phonon velocities of each component of the gas. Whatever the value of this ratio, we identify -- using the Renormalization Group and a variational calculation -- three types of phases, (i) a fully delocalized phase, that is a two-component Luttinger, (ii) a fully localized phase where both components are pinned by disorder and (iii) an intermediate phase where fermions are localized and bosons are superfluid. The second system is a two-leg ladder lattice of hardcore bosons. Three parameters control the physics: transverse and longitudinal tunneling and the filling. Using several analytical methods (perturbation theory, bosonization, RG) we give an interpretation of new numerical results obtained by our collaborators, namely on the Luttinger parameter of the symmetric mode. We deduce a phase diagram for weak disorder
Aspects topologiques des dérivés du graphène by Raphaël De gail( )

1 edition published in 2014 in French and held by 1 WorldCat member library worldwide

During the last few decades, condensed matter physics has witnessed a deep refoundation of its paradigms, through the discovery of many systems that the usual symmety classification à la Landau cannot handle properly. Although the first major breaktroughs were realized at the time of discovery of integer and fractional quantum Hall effects, only recently physicists have agreed that these peculiar phases of matter require neither a magnetic field nor low temperature. Those new states of matter cannot be caracterized by the geometric aspects of the model but rather by topological ones. The precise shape of the electronic spectrum is no longer relevant, but only particular features are, such as the presence or the absence of a gap. Similarly to the Landau classification scheme, one can achieve a construction through extensive use of topological groups. This is the realm of algebraic topology. Related generated topological invariants can hold a classification of non-trivial topological states, as well as of the accompanying transitions. This thesis focusses on peculiar topological features of two-dimesnsional electronic band structures. After a technical introduction to the underlying formalism, the first chapter is devoted to local topology, that is for a restricted piece of the first Brillouin zone, of band crossing points, also known as Dirac points. Special care is taken to classify these points and related transitions. The next chapter sheds some light on a particularly efficent way of measuring topology for two-dimensional electrons. This is achieved through measurements of Landau levels that are generated by a magnetic field applied perpendicular to a plane. Dirac points then generate zero Landau levels that are topologically stable, i.e. almost not influenced by perturbations at all. Distinctions between low and high magnetic fields will prove to be relevant, although very system-dependant. Through the several models studied, we particularly stress out the importance of the topological tool for condensed matter physics, past present... and future
 
moreShow More Titles
fewerShow Fewer Titles
Audience Level
0
Audience Level
1
  Kids General Special  
Audience level: 0.96 (from 0.81 for Collective ... to 0.99 for LES PREMIE ...)

Languages
English (13)

French (10)