Дисертації з теми "Effets topologiques"
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Mallet, François. "Cohérence quantique, diffusion magnétique et effets topologiques." Grenoble 1, 2006. https://theses.hal.science/tel-00546850.
In this thesis are reported experimental results centered on the thematic of the electronic quantum coherence at very low temperatures, obtained by very precise measurements of the quantum correction to the classical electronic transport in metallic nanostructures. We have first studied the coherence effects in network of metallic one-dimensional wires. We have shown the influence on the coherence itself of the diffusion dimensionality. By going from a macroscopic conductor to a purely mesoscopic one, we measured a crossover in the scaling of the quantum corrections amplitudes when the phase coherence length exceed the typical size of the system. This has allowed us to really precise what the ensemble averaging is in Mesoscopic Physics. In the second part of this work, we have shown the temperature dependence of the phase coherence length in metallic wire with magnetic impurities. These samples were fabricated in a very new and controlled way, by using a new technics with a focus ion beam. We have measured a universal behavior over 2 decades in temperature for the dephasing due to one magnetic impurity. This was the direct prove that this added decoherence belongs to the physics of the generic many body problem named « Kondo Physics ». We have finally shown that the measured dephasing rate was in excellent agreement with recent theoretical calculations based one the numerical renormalization group technics. More precisely we have shown that the magnetic impurities screening induces a linear desaturation of the phase coherence time above 0,1 TK
Bauchy, Mathieu, and Matthieu Micoulaut. "Contraintes topologiques et rigidité dans les verres." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2012. http://tel.archives-ouvertes.fr/tel-00805762.
Shevtsov, Oleksii. "Contribution à la théorie du transport quantique : isolants topologiques à base de graphène et phénomènes à fréquence finie." Phd thesis, Université de Grenoble, 2012. http://tel.archives-ouvertes.fr/tel-00770160.
Harman-Clarke, Adam. "Contraintes Topologiques et Ordre dans les Systèmes Modèle pour le Magnétisme Frustré." Thesis, Lyon, École normale supérieure, 2011. http://www.theses.fr/2011ENSL0659.
In this thesis a series of model frustrated magnets have been investigated. Their common parent is the spin ice model, which is transformed into the kagome ice and square ice models in two-dimensions, and an Ising spin chain model in one-dimension. These models have been examined with particular interest in the spin ordering transitions induced by constraints on the system: a topological constraint leads, under appropriate conditions, to the Kasteleyn transition in kagome ice and a lattice freezing transition is observed in square ice which is due to a ferromagnetic ordering transition in an Ising chain induced solely by finite size effects. In all cases detailed Monte Carlo computational simulations have been carried out and compared with theoretical expressions to determine the characteristics of these transitions. In order to correctly simulate the kagome ice model a loop update algorithm has been developed which is compatible with the topological constraints in the system and permits the simulation to remain strictly on the groundstate manifold within the appropriate topological sector of the phase space. A thorough survey of the thermodynamic and neutron scattering response of the kagome ice model influenced by an arbitrary in-plane field has led to a deeper understanding of the Kasteleyn transition, and a computational model that can predict neutron scattering patterns for kagome ice materials under any experimental conditions. This model has also been shown to exhibit quantised thermodynamic properties under appropriate conditions and should provide a fertile testing ground for future work on the consequences of topological constraints and topological phase transitions. A combined investigation into the square ice and Ising chain models has revealed ordering behaviour within the lattice that may be decoupled from underlying ferro- magnetic ordering and is particularly relevant to magnetic nanoarrays
Badiane, Mouhamadou Driss. "Propriétés hors équilibre des jonctions Josephson multi-terminales et topologiques." Thesis, Grenoble, 2013. http://www.theses.fr/2013GRENY057.
This PhD thesis manuscript deals with the non equilibrium transport properties of superconducting meso-scopic systems. This study declines in two shutters : i) signatures of Majorana fermions in topological Josephsonjunctions and ii) current-current correlations in three-terminal Josephson junctions.Majorana fermions appears at the boundaries of topological superconductors. When two topological su-perconductors are connected to form a Josephson junction, the zero-energy Majorana bound states localizedon either side of the junction form an Andreev bound state. As this current carrying state is 4π-periodic inthe superconducting phase difference, it was speculated that, at finite dc bias voltage, the junction exhibits afractional Josephson effect. We show that any finite phase velocity induces a dynamic coupling between thebound state and the continuum of states above the superconducting gap amplitude. This intrinsic couplingprovides an unavoidable mechanism that alters the fractional Josephson effect. We discuss, in terms of thecircuit parameters, signatures of the fractional Josephson effect that could be relevant for current experimen-tal investigations : the even-odd effect in Shapiro steps and the emergence of a peak at fractional Josephsonfrequency in the current noise spectrum. Furthermore, other manifestations of the Majorana bound states onthe subgap current-voltage characteristic are discussed.In a second step, we discuss the dissipative current fluctuations in three terminal Josephson junctions. Weshow that, current-current cross correlations can be positive and amplified in a coherent regime. This findingopens the possibility for further investigations on quantum entanglement in those systems
Repellin, Cécile. "Numerical study of fractional topological insulators." Thesis, Paris, Ecole normale supérieure, 2015. http://www.theses.fr/2015ENSU0028/document.
Topological insulators are band insulators which are fundamentally different from atomic insulators. Only a non-local quantity called topological invariant can distinguish these two phases. The quantum Hall effect is the first example of a topological insulator, but the same phase can arise in the absence of a magnetic field, and is called a Chern insulator. In the presence of strong interactions, topological insulators may host exotic excitations called anyons. The fractional quantum Hall effect is the only experimentally realized example of such phase. In this manuscript, we study the conditions of emergence of different types of fractional topological insulators, using numerical simulations. We first look at the fractional quantum Hall effect on the torus. We introduce a new projective construction of exotic quantum Hall states that complements the existing construction. We study the low energy excitations on the torus of two of the most emblematic quantum Hall states, the Laughlin and Moore-Read states. We propose and validate model wave functions to describe them. We apply this knowledge to characterize the excitations of the Laughlin state in Chern insulators. We show the stability of other fractional quantum Hall states in Chern insulators, the composite fermion, Halperin and NASS states. We explore the physics of fractional phases with no equivalent in a quantum Hall system, using two different strategies: first by choosing a model with a higher value of the topological invariant, second by adding time-reversal symmetry, which changes the nature of the topological invariant
Adroguer, Pierre. "Propriétés de transport électronique des isolants topologiques." Phd thesis, Ecole normale supérieure de lyon - ENS LYON, 2013. http://tel.archives-ouvertes.fr/tel-00832048.
Thomas, Candice. "Strained HgTe/CdTe topological insulators, toward spintronic applications." Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAY090/document.
With graphene-like transport properties governed by massless Dirac fermions and a topological protection preventing from backscattering phenomena, topological insulators, characterized by an insulating bulk and conducting surfaces, are of main interest to build low power consumption electronic building-blocks of primary importance for future electronics.Indeed, the absence of disorder, the generation of dissipation-less spin-polarized current or even the possibility to generate pure spin current without magnetic materials are some of the promises of these new materials.The objective of this PhD thesis has been to experimentally demonstrate the eligibility of HgTe three dimensional topological insulator system for applications and especially for spintronics.To do so, strong efforts have been dedicated to the improvement of the growth process by molecular beam epitaxy.Chemical composition, strain, defect density and sharpness of the HgTe interfaces have been identified as the major parameters of study and improvement to ensure HgTe inverted band structure, bulk gap opening and to emphasize the resulting topological surface state electronic properties. Verification of the topological nature of this system has then been performed using low temperature magneto-transport measurements of Hall bars designed with various HgTe thicknesses. It is worth noting that the high desorption rate of Hg has made the nanofabrication process more complex and required the development of a low temperature process adapted to this constraint. While the thicker samples have evidenced very complex transport signatures that need to be further investigated and understood, the thickness reduction has led to the suppression of any additional contributions, such as bulk or even side surfaces, and the demonstration of quantum Hall effect with vanishing resistance. Consequently, we have managed to demonstrate direct evidences of Dirac fermions by temperature dependent analysis of the quantum Hall effect. The next step has been to use the topological properties and especially the locking predicted between momentum and spin to test the HgTe potential for spintronics. Spin pumping experiments have demonstrated the power of these topological structures for spin injection and detection. Moreover, the implementation of HgTe into simple p-n junction has also been investigated to realize a first spin-based logic element
Le, calvez Kévin. "Signatures of a 4pi periodic Andreev bound state in topological Josephson junctions." Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAY099/document.
Three dimensional topological insulators (3D TI) are a new state of matter composedof an electrically insulating bulk covered by metallic surface states. Theoretically, a topo-logical Josephson junction composed of these surface states can host an Andreev Boundstate (ABS) that has twice the periodicity of the conventional 2p periodic ABSs. The4p periodic ABS is expected to be the building block of topological quantum computing.Therefore, we study the dynamic of this particular ABS by performing Shapiro measure-ment on Josephson junctions built with bismuth based 3D TI.To identify the e?ects of a 4p periodic ABS in a Shapiro measurement, we use a phe-nomenological model that simulates the voltage-current characteristics of a TJJ. We predicttwo signatures of the 4p periodic ABS and estimate their robustness against Joule heatingand thermally activated quasiparticle poisoning of the 4p periodic mode.We study the Josephson junctions dynamics by performing Shapiro measurements onjunctions built on Bi2Se3. We observe the two previously anticipated signatures, whichare the non-conventional appearance order of the Shapiro steps and the remaining of asupercurrent at the closing of the Shapiro step n = 0. They prove the presence of a 4pperiodic ABS.We also study the topological insulator BiSbTeSe2 that we have grown by using themelting growth method. By superconducting interferometric measurements, we show asuperconducting surface transport without bulk electronic conduction
Vistoli, Lorenzo. "Topological and electronic properties of electron-doped manganite thin films." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS113.
Oxide thin films feature a wide range of physical phenomena and rich phase diagrams tunable by strain and interface engineering. CaMnO3, in particular, is extremely sensitive to both doping and strain and, when grown with compressive strain, transitions from an insulating and antiferromagnetic state to a metallic and weakly ferromagnetic state at only 2% Ce doping.We used a combination of angle-resolved photoemission spectroscopy, magnetotransport, and density functional theory to study the electronic properties of this material. We observed the existence of two separate charge carriers, light electrons and heavy polarons, whose physical nature differs because of drastically different couplings to phonons. We ascribe these differences to a different relative band filling due to correlations, which enhance greatly the coupling to phonons of the heavy polarons band. Magnetotransport experiments reveal that the polaron band dominates transport despite its lower mobility.Compressive strain also gives rise to a strong magnetic anisotropy which stabilizes magnetic bubbles that accompany a topological Hall effect. This suggests that these bubbles have topological character, i.e. are skyrmion bubbles. The topological Hall effect diverges as the manganite approaches the metal-insulator transition at low dopings. We used a recently developed theory in order to interpret this behavior, and we conclude that correlations may come into play, enhancing the effective mass of the carriers, and in turn the topological Hall effect.As this manganite is highly sensitive to changes in doping and carrier density, we grew BiFeO3/(Ca,Ce)MnO3 ferroelectric field-effect transistors. Upon switching the ferroelectric polarization of the BiFeO3 top layer, we could not observe any sizable changes in the properties of the underlying manganite layers. We used transmission electron microscopy to study the properties of these bilayers with an atomic resolution, and we observed that polarization pinning at the BiFeO3/(Ca,Ce)MnO3 impedes a complete switch of the polarization and so reduces the operational capabilities of these devices. Nevertheless, we could detect modifications of the electronic properties of the manganite induced by polarization reversal at the atomic scale
Bouvier, Clément. "Preuves expérimentales d'un transport de surface sur un isolant topologique 3D HgTe/CdTe sus contrainte." Thesis, Grenoble, 2013. http://www.theses.fr/2013GRENY078/document.
This report deal with caracterisation of magnetotransport in HgTe/CdTe structures bulk strained in that a topological surface transport is predicted. This new kind of material is a 3D topological insulator.In this thesis, I will explain what means 3D/2D topological insulator before focusing on II-VI system lijke HgTe/CdTe.Next, I will discuss about growing conditions performed in CEA/Leti and then material caracterisation by X-ray. Surfaces band structures were also, observed by ARPES, underligned in the report.A third part deal with Hall bars design and conception in order to emphasize topological behavior of these surfaces.The last part shows the results obtained on these Hall bars with magnetotransport at low and high magnetic field. Ambipolaire behaviour, non trivial Berry phase, weak antilocalization and the interger quantum hall effect in HgTe/CdTe structures are studied and a possible interpretation of these results are given
Charlebois, Serge. "Étude expérimentale des excitations topologiques de l'effet Hall quantique à [nu] = 1 dans les hétérostructures semiconductrices à double puits quantique." Sherbrooke : Université de Sherbrooke, 2002.
Soussi, Fahd. "Effets de textures cristallographique, morphologique et topologique sur la conduction effective d'un milieu hétérogène." Metz, 1992. http://docnum.univ-lorraine.fr/public/UPV-M/Theses/1992/Soussi.Fahd.SMZ9238.pdf.
A new self consistent approach theory is formulated in the case of the electrical conductivity in the polycrystal. A self consistent approach is developed, where each grain is assumed to be a single ellipsoidal inclusion in a homogeneous equivalent medium. An interaction formula is derived and the electrical conductivity is calculated by resolving a linear system of equations. Applications to morphological and crystallographic effect are considered. We discuss in some details the contribution of our approach to the study of electrical conductivity of a composite medium constituded, for example, by spherical inclusions of conductivity k1 in a matrix of conductivity k2
SOUSSI, FAHD Molinari Alain. "EFFETS DE TEXTURES CRISTALLOGRAPHIQUE, MORPHOLOGIQUE ET TOPOLOGIQUE SUR LA CONDUCTION EFFECTIVE D'UN MILIEU HETEROGENE /." [S.l.] : [s.n.], 1992. ftp://ftp.scd.univ-metz.fr/pub/Theses/1992/Soussi.Fahd.SMZ9238.pdf.
Amaouch, Mohamed. "Applications des approches topologiques ELF et QTAIM dans un contexte quasirelativiste à 2 composantes." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066496/document.
This thesis deals with the aplication of topological approaches of the chemical bonding by means of analysing properties of density-based functions like Electron Localization Function (ELF) and the Quantum Theory of Atoms in Molecumes (QTAIM) to systems involving heavy elements such as 6p elements or actinides . It is divided into two main parts: (i) the evaluation of the spin-orbit coupling (SOC) effects on the electronic structure by means of combination of the QTAIM and ELF topological analyses in the field of quasirelativistic quantum calculations, and (ii) the rationalization of structural distorsions on molecules containing heavy atoms, and the role of the SOC on these distorsions. We were able to emphasize different situations for which SOC has strong, moderate or tiny influence on the chemical bonding, depending on the chemical environnement on which the heavy element is involved. In the second part of this thesis we tested our approach consisting of ELF/QTAIM interbasin repulsion energy analysis in connection with the molecular geometry of the system, in the spirit of the VSEPR and LCP models
Palin, Victor. "Heusler compounds for spin-orbitronics : exploration of topological effects and magnetic anisotropy engineering." Electronic Thesis or Diss., Université de Lorraine, 2023. http://www.theses.fr/2023LORR0031.
Over the last decades, the needs in storage capacity as shot up with computing development. The energy crisis that we are going through in the 21th century requires to develop new fundamental materials for data storage. It was with this purpose that physicist develop new ways to store information in order to reduce device’s scale, energy consumption and manufacturing cost while memories’ size and information’s speed has shot up. The research conducted in this thesis make use of two different ways to improve data storage:- The first one is by using emerging materials in science, called topological insulator, that host peculiar spin texture predicted to generate very high spin-to-charge interconversion. This non-trivial state of matter can be complex to stabilize and image. This is the goal of the first part of this thesis where topological insulators coming from the half-Heusler family are engineered by molecular beam epitaxy. Structural characterization are carried out by X-ray and electronic diffraction along with scanning tunneling microscopy and transmission electron microscopy that confirm an epitaxial growth in the desired structure predicted to host a non-trivial topology. Angle resolved photoemission spectroscopy is performed and reveals the presence of linear states around the Γ point of the Brillouin zone. Nonetheless, the complex Fermi surfaces imaged do not allow to draw clear conclusions on the non-trivial nature of both alloys. Transport measurements were performed to test the potential interconversion efficiency of our compounds and spin Seebeck experiments revealed a spin-to-charge conversion two to three times higher in our TIs compared to a Pt control sample.- The second way chosen to improve conventional magnetic memories is by playing with magnetic anisotropy. Here again, Heusler family offers a vast variety of compounds allowing to fulfill this goal. The Mn3Z family compounds has attracted a lot of attention owing to their tetragonalized unit cell that allows to stabilize perpendicular magnetic anisotropy (PMA) even in a thin film geometry. In this thesis, we investigate Mn(100-x)Ga(x) and Mn(100-x)Ge(x) alloys and manage to stabilize them in their D0(22) structure that offers PMA. A peculiar zoom is then done on Mn3Ge-based stacks composed of a second Heusler alloy with remarkable properties, the Co2MnZ’ family (Z' = Si, Ge). Co2MnZ’ compounds have a half-metallic behavior making them very suitable for spin transfer torque related applications due to their low magnetic damping and full spin polarization at the Fermi level. Here we develop Mn3Ge/Co2MnZ' heterostructures (bilayers and superlattices) and manage to grow both compounds in the desired structures. The overall system is perpendicularly magnetized (thanks to Mn3Ge), terminated with a half-metal magnet (thanks to Co2MnZ') and the thicknesses used for both layers allow to tune the magnetic properties and obtained 100% of remanence
Razo, López Luis Alberto. "Localisation des ondes électromagnétiques au-delà d'Anderson : rôle des corrélations, des symétries et de la topologie." Electronic Thesis or Diss., Université Côte d'Azur, 2024. http://www.theses.fr/2024COAZ5013.
In a broad sense, the term wave localization refers to a phenomenon where waves are spatially confined in small regions of the space without any bounding material barriers.In this Thesis, we investigate (analytically, numerically and experimentally) different physical collective mechanisms to spatially localize, and therefore, to control electromagnetic waves. Specifically, we focus on the role of uncorrelated and correlated potentials, as well as of topological effects to achieve wave confinement. Analytical and numerical studies are accomplished in the framework of a recent approach in the modeling of Anderson localization called localization landscape theory. On the other hand, experiments are performed using a microwave platform composed by small dielectric cylinders placed inside a cavity made of two metallic plates. The cavity implements a propagative wave system, where we can efficiently control the local permittivity by means of the cylinders acting as scatterers, or as an analogic tight-binding system, where, in this case, the dielectric cylinders play the role of resonators.First, we extend the scope of the localization landscape approach to a wide class of one and two dimensional tight-binding systems in the presence of uncorrelated disorder, where localized eigenfunctions appear in both band-edges. We demonstrate how the landscape theory is able to predict accurately not only the locations, but also the energies of localized eigenfunctions in the low- and high-energy regimes. Later, by using our experimental cavity as a propagative system, we perform microwave transport experiments in two dimensional planar arrays. Experiments are carried out on a disordered lattice and on an aperiodic Vogel spiral from where we characterize the electromagnetic modal structures in real space. Our results reveals that aperiodic systems can carry a rich variety of long-lived modes—with Gaussian, exponential, and power law spatial decays—which are able to survive even in a three-dimensional environment. This is supported by different transport quantities such as the density of states, the characteristic decay time, and the Thouless conductance that are also experimentally accessible. On the contrary, we show that the eigenstates in traditional disordered media are always limited to exponential radial decays with leaking features beyond two-dimensions.Finally, we use the experimental tight-binding configuration to investigate the propagation of topological helical states. Particularly, we experimentally analyze a set of honeycomb-like structures built using a triangular lattice with an hexagonal unit cell, which are characterized by the Z_2 topological invariant. By recovering the modal structure in real space and the density of states, our results reveal the possibility to open a topological gap, dwelt by edge states that lives in the border of the structure.We demonstrate the unidirectional counterpropagative features of such helical edge states.Taken together, our results demonstrate that it is possible to model, control and localize electromagnetic waves not only within, but beyond Anderson's conception. Thanks to the crossroads we have taken, we have mapped out an itinerary that brings us closer to the main avenue leading perhaps to Anderson localization of three dimensional electromagnetic waves
Sanogo, Satafa. "Conception optimale de circuits magnétiques dédiés à la propulsion spatiale électrique par des méthodes d'optimisation topologique." Thesis, Toulouse 3, 2016. http://www.theses.fr/2016TOU30015/document.
In this work, we present theoretical and numerical optimization method for designing magnetic circuits for Hall effect thrusters. These design problems are very difficult inverse ones that we formulate under the form of topology optimization problems. Then, the obtained problems are non convex subject to Maxwell equations like constraints. Some original approaches have been proposed to solve efficiently these topology optimization problems. These approaches are based on the material density model called SIMP approach (Solid Isotropic Material with Penalization) which is a variante of the homogenization method. The results in my thesis allowed to provide optimization source code named ATOP (Algorithm To Optimize Propulsion) unsung in parallel two scientific computing softwares namely Matlab and FEMM (Finite Element Method Magnetics). In ATOP, we use both local optimization algorithms based on sensitivity analysis of the design problem; and global optimization algorithms mainly of type Branch and Bound based on Interval Arithmetic analysis. ATOP will help to optimize both the topological shape of the magnetic circuits and the time and cost of production (design process) of new generations of electrical thrusters
Sticlet, Doru Cristian. "États de bord dans les isolants de Chern et les fermions de Majorana dans les supraconducteurs topologiques." Phd thesis, Université Paris Sud - Paris XI, 2012. http://tel.archives-ouvertes.fr/tel-00770666.
Flayac, Hugo. "Nouvelles tendances dans les condensats d'exciton-polaritons spineurs : défauts topologiques et structures de basse dimensionnalité." Phd thesis, Université Blaise Pascal - Clermont-Ferrand II, 2012. http://tel.archives-ouvertes.fr/tel-00822148.
Artaud, Alexandre. "Quasi-ordre à longue distance et défauts topologiques dans le graphène sur rhénium étudié par microscopie à effet tunnel." Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAY009/document.
The discovery of graphene in 2004 is a two-fold breakthrough in condensed matter physics. On the one hand, its electronic properties are that of a massless Dirac fermion gas. On the other hand, its structure is the very first example of an ordered material in two dimensions.This second characteristics is studied in this thesis by scanning tunneling microscopy (STM), in the case of graphene grown in ultra-high vacuum on the (0001) surface of rhenium. In two dimensions, crystalline order is indeed impossible, and it is predicted to be replaced by a quasi-long-range order, for which the phase of the order parameter fluctuates. The rhenium substrate then acts as an outside influence that can restore crystalline order, as it forces graphene's structure to adopt an epitaxial relation with rhenium.The study of graphene's structure proposed here proves it actually originates from kinetic constraints inherited from its growth. Many typical nanostructures have indeed been identified at the atomic scale, giving access to the growth mechanism. Two reaction pathways compete. The first one gives rise to a family of metastable carbon clusters with well-defined structures in epitaxy on rhenium. The second one leads to growing graphene islands of a few nanometers in size. The coalescence of these islands and the incorporation of the carbon clusters ends up forming structural defects whose atomic structure is detailed for the first time. This exhaustive study reveals reaction pathways in the growth of graphene on rhenium are diverse, and constitute compromises between kinetics and thermodynamics.At the end of that growth, the obtained graphene is not uniform, but made of roughly 10 nm-large domains. Each domain displays a specific epitaxial relation with rhenium, in which graphene is both twisted and sheared with respect to rhenium, as revealed a STM image analysis method developed for this purpose. Elaborating a universal classification of such epitaxial relations shows they are very diverse. Two interpretations of this morphology are possible. The graphene domain walls can indeed be interpreted as topological defects in the crystalline order set in graphene by the rhenium substrate. Otherwise, they are fluctuation modes whose dynamics is frozen by the interaction with the substrate. These results put into question the notion of crystalline order set by a substrate to a two-dimensional material. They show that instead of forcing a specific epitaxial relationship, the graphene-substrate interaction gives rise to a so-called chaotic phase
Guillet, Thomas. "Tuning the spin-orbit coupling in Ge for spin generation, detection and manipulation." Thesis, Université Grenoble Alpes, 2020. http://www.theses.fr/2020GRALY033.
One of the main goals of spintronics is to achieve the spin transistor operation and for this purpose, one has to successfully implement a platform where spin currents can be easily injected, detected and manipulated at room temperature. In this sense, this thesis work shows that Germanium is a very good candidate thanks to its unique spin and optical properties as well as its compatibility with Silicon-based nanotechnology.Throughout the years, several spin injection and detection schemes were achieved in Ge but the electrical manipulation of the spin orientation is still a missing part. Recently we focused on two approaches in order to tune the spin-orbit interaction (SOI) in a Ge-based platform. Both rely on the structural inversion asymmetry and the spin-orbit coupling at surfaces and interfaces with germanium (111). First, we performed the epitaxial growth of the topological insulator (TI) Bi2Se3 on Ge (111). After characterizing the structural and electrical properties of the Bi2Se3/Ge heterostructure, we developed an original method to probe the spin-to-charge conversion at the interface between Bi2Se3and Ge by taking advantage of the Ge optical properties. The results showed that the hybridization between the Ge and TI surface states could pave the way for implementing an efficient spin manipulation architecture.The latter approach is to exploit the intrinsic SOI of Ge (111). By investigating the electrical properties of a thin Ge(111) film epitaxially grown on Si(111), we found a large unidirectional Rashba magnetoresistance, which we ascribe to the interplay between the externally applied magnetic field and the current-induced pseudo-magnetic field in the spin-splitted subsurface states of Ge (111). The unusual strength and tunability of this UMR effect open the door towards spin manipulation with electric fields in an all-semiconductor technology platform.In a last step, I integrated perpendicularly magnetized (Co/Pt) multilayers-based magnetic tunnel junctions on the Ge (111) platform. I developed an original electro-optical hybrid technique to detect electrically the magnetic circular dichroism in (Co/Pt) and perform magnetic imagingThese MTJs were then used to perform spin injection and detection in a lateral spin valve device. The perpendicular magnetic anisotropy (PMA) allowed to generate spin currents with the spin oriented perpendicular to the sample plane.Finally, I assembled all these building blocks that were studied during my PhD work to build a prototypical spin transistor. The spin accumulation was generated either optically or electrically, using optical spin orientation in germanium or the injection from the magnetic tunnel junction
Sticlet, Doru. "Edge states in Chern Insulators and Majorana fermions in topological superconductors." Thesis, Paris 11, 2012. http://www.theses.fr/2012PA112318/document.
This thesis follows two threads in the field of topological insulators and superconductors. The first part of the thesis is devoted to the study of two-dimensional quantum anomalous Hall insulators on a lattice, in the absence of an external magnetic flux, but induced by an inhomogeneous flux in the unit cell. The system possesses several gapped phases characterized by a topological invariant, the Chern number, that is related to the conductance carried by the edge states. Here we show that two-band models admit an arbitrary large number of Chern phases or, equivalently, an arbitrary number of edge states, by adding hopping between distant neighbor sites. This result is based on a formula proving that the Chern number of a band depends on certain properties of a finite set of points in the Brillouin zone, i.e. the Dirac points for the gapless system. These ideas are made more concrete in the study of a modified Haldane model, and also by creating an artificial model with five Chern phases, whose edge states are determined in detail. The second part of the thesis focuses on one-dimensional topological superconductors with exotic zero-energy edge states: the Majorana bound states. Here we investigate the presence of Majorana fermions in spin-orbit coupled semiconducting wire in proximity to an s-wave superconductor. We show that the spin-polarization of the electronic degrees of freedom in the Majorana wave function depends on the relative weight of Dresselhaus and Rashba spin-orbit couplings. We also investigate Majorana fermions in linear superconductor-normal and long superconductor-normal-superconductor (SNS) junctions where they appear as extended states in the normal junction. Furthermore, ring geometries can be mapped to an SNS junction, and, we have shown that under the action of superconducting phases gradients, extended Majorana fermions can form again inside the normal wire. Finally a two-band model with multiple Majorana fermions is treated and we show that Josephson junctions built from this model maintain the 4π periodicity for the fractional Josephson effect, one of Majorana fermions signatures
Noel, Paul. "Dynamical spin injection and spin to charge current conversion in oxide-based Rashba interfaces and topological insulators." Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAY062.
Using a ferromagnetic layer has been the first method to obtain and detect spin currents, allowing to modify the magnetization state of an adjacent layer using spin transfer torque. However, in recent years, an alternative way to manipulate spin currents has been proposed. An emerging field of spintronics, called spin-orbitronics, exploits the interplay between charge and spin currents enabled by the spin-orbit coupling (SOC) in non-magnetic systems. An efficient current conversion can be obtained through the Spin Hall Effect in heavy metals such as Platinum or Tantalum. The conversion can also be obtained by exploiting the Edelstein Effect in Rashba interfaces and topological insulators.The spin to charge conversion by means of Inverse Edelstein Effect and inverse Spin Hall Effect can be studied by the spin pumping by ferromagnetic resonance technique. This manuscript present these two conversion mechanisms as well as the technique that was used to measure them, which is based on an electrical detection of the ferromagnetic resonance. Results on the spin to charge current conversion obtained in metals, oxide-based Rashba interfaces and topological insulators will be presented. Among these systems we have demonstrated the possibility to tune the conversion efficiency by using a gate voltage in a two-dimensional electron gas at the surface of an oxide SrTiO3. Moreover it is possible to tune this effect, a remanent way, thanks to the ferroelectricity obtained in SrTiO3 at cryogenic temperatures.Other studied systems such as topological insulators HgTe and Sb2Te3 also have promising properties for an efficient spin to charge current conversion at room temperature. In particular we showed than in HgTe by using a thin HgCdTe protective layer, it is possible to obtain a spin to charge current conversion efficiency one order of magnitude larger than in Pt.These results suggest that stwo dimensional electron gases at oxide interfaces and topological insulators have a strong potential for the efficient detection of spin currents for possible beyond CMOS applications
Etienne, Thibaud. "Développement et application de stratégies d’étude théorique de propriétés remarquables relatives aux états excités moléculaires." Thesis, Université de Lorraine, 2015. http://www.theses.fr/2015LORR0097/document.
Exploiting theoretical methods for modeling remarkable molecular properties has extensively gained interest from the scientific community during the last few decades. The development of these methods has been made possible by the important technological progresses realized in the field of computational science. These advances made accessible some informations that are crucial to our current researches but hitherto impossible to compute. It is thus now possible to solve high-level theoretical issues and to access novel critical properties. Within this framework, quantum-mechanical characterization of molecular excited states still constitutes a challenging achievement with a considerable interest to the theoretical and experimental molecular physics community. However, these studies can be of extreme complexity, due to the interplay between numerous physical phenomena that characterize the access of a system to its own excited states. The scope of our contribution is closely related to these fundamental issues in the sense that we aim at rationalizing the behavior of chromophores facing a photon capture. This light-matter interaction is studied at the molecular level and is addressed in our work with quantum-mechanical methods in order to unravel the mechanisms inherent to the characteristic properties of target compounds. Those interpretations are supported by theoretical developments intending the establishment or consolidation of conceptual and mathematical tools constituting our theoretical strategy for excited states investigations. The aforementioned developments are mostly related to the interaction of chromophores with their molecular vicinity treated implicitely or explicitely, the latter playing an important role in our attempt to gain a geometrical resolution of electronic spectra with conformational space sampling methods. Our interest was also focused on the photoinduced electronic structure reorganization through the design of quantum-mechanical descriptors of excited states topology. On the other hand, applications were related to chromophores exhibiting remarkable molecular properties : solvatochromic probe, explosive probe, chromophore interacting with DNA, dyes designed for third-generation solar cells, multichromophoric clusters
Smagghe, Guillaume. "modélisation de la recristallisation lors du forgeage à chaud de l’acier 304L – une approche semi-topologique pour les modèles en champs moyens." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEM003/document.
Cooling system of nuclear power plants is constituted of metallic parts obtained by hot forging. Thus during the manufacturing process, the microstructural trans- formations induced by the deformation and annealing process define partially the mechanical properties of the final products. A sharp knowledge of the physical mechanisms generated within the material is required to handle the microstructure. In the case of hot deformation of 304L austenitic stainless steel, the microstructural modifications depend on the discontinuous dynamic recrystallization (DDRX) and the post-dynamic recrystallization (PDRX). The aim of this project is: (i) the study of the DDRX and the PDRX under the conditions of deformation inherent in the forging process, (ii) the study of the influence of niobium addition on these mechanisms, (iii) the modeling of these me- chanisms in order to predict the microstructure characteristics (mean grain size and distribution) following a multipass process. As part of the research, the deformation conditions experienced during the hot forging process are replicated through torsion tests with model materials containing various niobium concentrations. Characterization and modeling of microstructures enable to understand the respective e ects of temperature, strain rate as well as niobium addittion on the DDRX and PDRX mechanisms. In this study, a new topological approach of mean-field hypothesis is developed in order to allow the prediction of realistic grain size distributions
Nalitov, Anton. "Spin dynamics ande topological effects in physics of indirect excitons and microcavity polaritons." Thesis, Clermont-Ferrand 2, 2015. http://www.theses.fr/2015CLF22569/document.
The present thesis manuscript is devoted to new phenomena in physics of light-matter quasiparticles in heterostructures, related to spin and topology. It is divided into four parts. Chapter 1 gives a necessary background, introducing basic properties of microcavity polaritons and indirect excitons in coupled quantum wells. Chapter 2 is focused on spin dynamics and topological defects formation in indirect exciton many-body systems. The last 2 chapters are related to microcavity-based structures. Chapter 3 is devoted to polariton spin dynamics in optical parametric oscillators. Finally, Chapter 4 studies pillar microcavity lattices and introduces the polariton topological insulator
Nacenta, Mendivil Jorge P. "Imagerie directe de champ électrique par microscopie à balayage d'un transistor à électron unique." Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAY009/document.
In this doctoral work, we have developed a new scanning single electron transistor (SET) microscope that works at very low temperatures (T = 50 mK) and high magnetic fields (B = 18 T). A SET consists of a small metallic island connected to source and drain electrodes through two tunnel junctions. In the Coulomb blockade regime at low temperature regime (T 5 K), an external electric field tunes the current circulating through the SET. In addition,small electric field variations lead to large SET current changes that makes the device a highly sensitive charge detector, able to detect charges smaller than 0.01 e. Thus, when the SET scans above a surface, it maps the electrostatic properties of the sample. However, the implementation of a scanning SET microscope is extremely challenging since it combines scanning probe microscopy, low temperatures and sensitive nanoscopic devices. For thisreason, only a few groups have succeeded its realization. Our technological choices to build the microscope improve certain aspects with respect to the already existing instruments. The breakthrough is that we fabricate the SET probe using standard lithographic techniques on commercial silicon wafers.For that reason, batch fabrication of SET probes is possible. Furthermore, by a combination of dicing and etching techniques, the SET is engineered extremely close to the edge of the Si chip (< 1 micrometer). In this way, the SET can be approached to a few nanometer from the sample surface by means of a atomic force distance control. Additionally, an on-probe gate electrode fabricated close to the island can be used to tune the operating point of the SET. Anovelty of our instrument is that with this on-probe gate and a feedback loop we have been able to map directly the local electric field. We demonstrate this new feedback scanning method by imaging an interdigitated array of nanometer scale electrodes. Moreover, the SET is an ideal tool for the study of the localization of electronic states. In the future, our scanning SET will be used for the study of two-dimensional electron systems in the quantum Hall regime, topological insulators and the metal insulator transition
Nicolaï, Laurent. "Couches minces de Bi et nouveaux composants : les effets du couplage spin-orbit dans la structure électronique." Thesis, Cergy-Pontoise, 2017. http://www.theses.fr/2017CERG0913/document.
In this thesis, we explore bismuth based materials that may exhibit topological properties. Bi is a parent compound of known Topological Insulators which consist of an insulating bulk while also presenting topologically protected conducting electronic surface states. In particular, these surface states are spin polarised and are protected by time-reversal symmetry. The dual appeal of topological insulators stems not only from their obvious interest from a fundamental physics point of view, but also from the fact that they may find use in spintronics and quantum computing.In those systems the spin-orbit coupling plays a central role. Spin-orbit coupling can also lead to the Rashba or Dresselhaus splitting, phenomena arising from the symmetry breaking respectively engendered by the surface/interface of a system or from the inherent atomic crystal structure.The interpretation of measured spin dependent band structure, as observed in (Spin-) and Angle-Resolved Photoemission Spectroscopy, was supported and completed by ab-initio Korringa-Kohn-Rostoker electronic structure calculations which account for all aspects of the investigated systems: in particular spin-orbit coupling, fundamentally included thanks to a fully relativistic approach.We first deposited Bi thin films onto a InAs(111) substrate. A crystal of Bi of very high quality was grown, confirmed by reproduction of the measured electronic bands by theoretical investigation. In parallel to Bi film growth, we observed that In and Bi form InBi crystals, exhibiting topological surface states. Our theoretical analyses confirm that these surface states are spin polarised.In the second part of the thesis, Bi was used as a dopant within InAs, forming an InAsBi alloy system. The strong spin-orbit coupling brought on by Bi generated simultaneously measurable Rashba and Dresselhaus effects, consequently splitting surface states in a completely atypical manner, giving non-helical spin polarised states
Soulé, Paul. "Étude des Bords des Phases de l’Effet Hall Quantique Fractionnaire dans la Géométrie d’un Contact Ponctuel Quantique." Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112215/document.
I present in this thesis a study that I did in the university Paris-sud under the supervision of Thierry Jolicœur onto Fractional Quantum Hall (FQH) phases in the cylinder geometry. After a short introduction in the first chapter, I present some basic concept relative to the FQH effect in the second one and introduce some essential features relative to the cylinder geometry, useful for the chapters 3, 4, and 5. The chapter 3 is dedicated to the study of the thin cylinder limit, i.e. when the circumference of the cylinder is of the order of a few magnetic length. In this limit, it is known that the Laughlin wave function at the filling factor 1/q is reduced to a one dimensional crystal in the lowest Landau level orbitals where one every q orbitals is occupied. We Taylor expand the Hamiltonian when the circumference is small compare to the magnetic length in order to study an intermediate limit. When only the first four terms of the development are kept, it is possible to find exact representations of the ground state with "squeezing" operators or matrix products. We also find similar representations for quasiholes, quasielectrons and the magnetorton branch. These results have been published in the article Phys. Rev. B 85, 155116 (2012). In the chapter 4 and 5 I focus onto the gapless chiral edge excitations of FQH phases. I present a microscopic study of those edges states in the cylindrical geometry where quasiparticles are able to tunnel between edges. I first study the principal FQH phase at the filling fraction 1/3 whose ground state is well described by the Laughlin wave function in the chapter 4. For an energy scale lower than the bulk gap, the effective theory is given by a very peculiar one dimensional electron fluid localized at the edge: a chiral Luttinger liquid. Using numerical exact diagonalizations, we study the spectrum of edge modes formed by the two counter-propagating edges on each side of the cylinder. We show that the two edges combine to form a non-chiral Luttinger liquid, where the current term reflects the transfer of quasiparticles between edges. This allows us to estimate numerically the Luttinger parameter for a small number of particles and find it coherent with the one predicted by X. G. Wen theory. We published this work in Phys. Rev. B 86, 115214 (2012). I then analyze edge modes of the FQH phase at filling fraction 5/2 in the chapter 5. From a Conformal Field Theory (CFT) based construction, Moore and Read (Nucl. Phys. B, 1991) proposed that the essential physics of this phase is described by a paired state of composite fermions. A striking property of this state is that emergent excitations braid with non-Abelian statistics. When localized along the edge, those excitations are described through a chiral boson and a Majorana fermion. In the cylinder geometry, we show that the spectrum of edge excitations is composed of all conformal towers of the IsingxU(1) model. In addition, with a Monte Carlo method, we estimate the various scaling dimensions for large systems (about 50 electrons), and find them consistent with the CFT predictions.In the last chapter of my manuscript, I present a work that I did in UBC (Vancouver) in collaboration with Marcel Franz onto quantum spin Hall phases in graphene induced by adatoms. In this system, adatoms induce a spin orbit coupling for electrons in the graphene sheet and create some disorder which might be responsible for destruction the spectral gap. We show in this chapter and in the article [Phys. Rev. B 89, 201410(R) (2014)] that the spectral gap remains open for a realistic range of parameters. In addition, with analytical computations in the low energy approximation and numerical exact diagonalizations, we find characteristic signal in the local density of states highlighting the presence of topological gap. This signal might be observed in scanning tunneling spectroscopy experiments
Bleu, Olivier. "Physics of quantum fluids in two-dimensional topological systems." Thesis, Université Clermont Auvergne (2017-2020), 2018. http://www.theses.fr/2018CLFAC044/document.
This thesis is dedicated to the description of both single-particle and bosonic quantum fluid Physics in topological systems. After introductory chapters on these subjects, I first discuss single-particle topological phenomena in honeycomb lattices. This allows to compare two theoretical models leading to quantum anomalous Hall effect for electrons and photons and to discuss the photonic quantum valley Hall effect at the interface between opposite staggered cavity lattices.In a second part, I present some phenomena which emerge due to the interplay of the linear topological effects with the presence of interacting bosonic quantum fluid described by mean-field Gross-Pitaevskii equation. First, I show that the spin-anisotropic interactions lead to density-driven topological transitions for elementary excitations of a condensate loaded in the polariton quantum anomalous Hall model (thermal equilibrium and out-of-equilibrium quasi-resonant excitation configurations). Then, I show that the vortex excitations of a scalar condensate in a quantum valley Hall system, contrary to linear wavepackets, can exhibit a robust chiral propagation along the interface, with direction given by their winding in real space, leading to an analog of quantum spin Hall effect for these non-linear excitations. Finally, coming back to linear geometrical effects, I will focus on the anomalous Hall effect exhibited by an accelerated wavepacket in a two-band system. In this context, I present a non-adiabatic correction to the known semiclassical equations of motion which can be expressed in terms of the quantum geometric tensor elements. We also propose a protocol to directly measure the tensor components in radiative photonic systems
Vilamot, Raphaël. "Optimisation de la configuration magnétique d'un propulseur à effet Hall par résolution du problème magnétostatique inverse." Phd thesis, Toulouse, INPT, 2012. http://oatao.univ-toulouse.fr/14668/1/vilamot.pdf.
Rocher, Jonathan. "Contraintes cosmologiques sur la physique de l'univers primordial." Phd thesis, Université Paris Sud - Paris XI, 2005. http://tel.archives-ouvertes.fr/tel-00011226.
Une étude de la contribution relative de ces cordes cosmiques aux anisotropies de température pour les deux modèles standards d'inflation hybride supersymétrique permet de montrer qu'ils sont tous deux en accord avec les observations, contrairement à ce que l'on pensait. Les contraintes fortes sur la contribution admissible des cordes aux CMB se traduisent alors en contraintes fortes sur tous les paramètres des modèles inflationnaires : constantes de couplage et échelle d'énergie de l'inflation. A la lumière de ces nouvelles contraintes, il devient possible de s'exprimer quant à l'aspect naturel de ces théories. On montre ainsi qu'ils souffrent de la nécessité d'ajuster finement leurs constantes de couplage : ceci est définitivement reconnu comme non naturel.
La contrainte sur la phase inflationnaire est aussi étudiée du point de vue de l'extraction de ses paramètres à partir des données d'expériences futures d'observation de la polarisation du CMB. Des outils statistiques permettant de mesurer les paramètres cosmologiques et d'estimer l'erreur sur ces estimations sont numériquement implémentés. L'effet de lentille gravitationnelle sur ces outils est ensuite étudié analytiquement et numériquement. Cela permet de valider l'approximation usuelle qui consiste à négliger l'effet de lentille sur la non gaussianité des données du CMB, à travers leur fonction de corrélation à quatre points.
Walter, Jean-Charles. "Etude numérique des corrections d'échelle au comportement dominant à l'équilibre et hors de l'équilibre." Phd thesis, Université Henri Poincaré - Nancy I, 2009. http://tel.archives-ouvertes.fr/tel-00440099.
Murani, Anil. "Supraconductivité par effet de proximité dans des nanofils de bismuth monocrystallins." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS093/document.
The superconducting proximity effect is a phenomenon occurring at low temperatures that conveys superconducting properties to a phase coherent normal metal sample connected to superconducting electrodes. It is also a powerful tool in mesoscopic physics because it is sensitive to different transport regimes at low temperatures. In particular, we have used this effect to reveal the special electronic transport properties of single crystal Bi nanowires. In this system, the transport is dominated by surface states. Moreover, the presence of strong spin-orbit coupling in Bi at low dimensions deeply influences its electronic structure : it was predicted that (111) oriented Bi bilayer are insulating in the bulk, but conducting along the edges. This so called Quantum Spin Hall Effect (QSHE), gives rise to counterpropagating chiral edge states, that are protected against disorder as long as time reversal symmetry is present.Through the observation of the resilience of the critical current in several samples at high magnetic field, along with SQUID-like interference pattern at low magnetic field, we showed the existence of supercurrent carrying 1D edge states. The measurement of the current-phase relation using the asymetric SQUID technique on a previously characterized nanowire was realized and further demonstrates that these edge states are ballistic. These findings are consistent with tight-binding simulations that extend the known results for (111) Bi bilayer to nanowire-like system. The addition of an in-plane Zeeman field allows one to observe 0-π transitions, thereby revealing spin-splitting induced Andreev level crossings. Finally, microwave spectroscopy measurement of the dynamical susceptibility in this system are initiated, that could reliably demonstrate the property of protection against disorder according to numerical simulations.By exploring Bi at low dimensions, this thesis paves the way towards the exploration of electronic states fully protected from disorder
Wang, Hangtian. "Interfacial Engineering of the Magnetism in 2D Magnets, Topological Insulators, and Their Heterostructures." Electronic Thesis or Diss., Université de Lorraine, 2023. http://www.theses.fr/2023LORR0206.
With the critical node of integrated circuits (IC) entering the 1 nm stage, traditional three-dimensional materials cannot maintain their original physical properties, and thus cannot meet the needs of IC manufacturing processes. Meanwhile, the shrinking line width also introduces an inevitable increase in static power consumption. Therefore, researching new materials and new technologies to break through the "Size Wall" and "Power Wall" has become a crucial direction in the IC industry. As a new member of the two-dimensional (2D) material family, the 2D magnets can maintain its long-range magnetic order at the atomic scale with its physical properties easily controlled by external stimuli, which provides an ideal platform for the high-density and low-power spintronic devices. However, due to the dimensional effect, 2D magnetism cannot exist at high temperatures. Although several methods can enhance the Curie temperature (Tc) of 2D magnets (such as doping, ion intercalation, or laser pumping), they are far from easy-controllability and high-efficiency. More importantly, the widely-used preparation method via mechanical exfoliation abandons the merit of 2D interfacial effect, which was proved to be an important approach to efficient 2D magnetic manipulation. Therefore, studying the interfacial effect in epitaxial 2D magnets is regarded as a key field to achieving large-scale, high-Tc, easy-controlling, and stable 2D ferromagnetic order. Topological insulator (TI) is another 2D material with strong spin-orbital coupling. The topology-protected surface states provided TI with numerous fascinates spin-related effects, such as spin-momentum locking, spin exchange effect, etc., which makes this material a potential candidate to fabricate effective spintronic devices. In addition, the TI can be integrated with 2D magnets to form a 2D heterostructure, in which not only the magnetism can be enhanced via the interfacial effect, but also the spin-related properties of the heterostructure can be manipulated due to the advantages of these two materials
Sterdyniak, Antoine. "Etude de l'intrication dans l'effet Hall quantique fractionnaire." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2013. http://tel.archives-ouvertes.fr/tel-00967926.
Taillefumier, Mathieu. "Quelques mécanismes non conventionnels de l'effet Hall anormal." Phd thesis, Université Joseph Fourier (Grenoble), 2006. http://tel.archives-ouvertes.fr/tel-00012052.
premières parties sont axées sur l'étude de quelques mécanismes
intrinsèques de l'effet Hall anormal. Nous montrons notamment que la
diffusion des porteurs de charge par des impuretés ou des défauts
donne une contribution intrinsèque non négligeable à l'effet Hall
anormal. Nous proposons ensuite une expérience, basée sur un réseau de
nanocylindres magnétiques, placé au dessus d'un gaz d'électrons
bidimensionnel, dans laquelle les contributions intrinsèques de
l'effet Hall anormal sont clairement identifiables et contrôlables.
Enfin, nous abordons le problème du mécanisme de chiralité de spin
proposé pour expliquer l'effet Hall dans le composé pyrochlore
Nd$_2$Mo$_2$O$_7$. En utilisant un modèle de gaz sur réseau ainsi
qu'une configuration magnétique non colinéaire (chirale), nous
montrons que la conductivité transverse a une dépendance complexe par
rapport à la chiralité de spin.
La dernière partie de ce manuscrit est dédiée à l'étude de quelques
propriétés des gaz d'électrons soumis à un champ magnétique
inhomogène. Après un bref rappel sur la dynamique d'électron en
présence d'un gradient de champ magnétique constant, nous abordons le
problème d'un champ magnétique périodique spatialement. En calculant
quelques états de Bloch aux points de haute symétrie, nous montrons qu'il
existe des états pour lesquels les électrons sont localisés au
voisinage des lignes de champ nul. Le calcul des courants de
probabilité montre que ces états sont porteurs de courants permanents
dont l'origine est liée aux inhomogénéités du champ magnétique au
voisinages des lignes de champ nul.
Ben, terdayet Insaf. "Étude de l'influence de la matrice sur le processus d'inférence de source des liquides inflammables par une approche chimiométrique non ciblée." Electronic Thesis or Diss., Université Paris sciences et lettres, 2023. http://www.theses.fr/2023UPSLC013.
Identifying the perpetrator of arson is a real challenge of criminal investigation since the physical traces associating a perpetrator with this type of crime scene are often destroyed by fire or extinguishing procedures. If an ignitable liquid was used to start the fire, and its residual presence can be detected, a source inference approach with other ignitable liquids is likely to provide investigative or evidentiary support. Source inference is a process of association, a method that consists of evaluating the possible common source between two unknown (traces of) ignitable liquids, in particular between a trace of a liquid extracted from a sample taken at the scene of the fire and a liquid found outside the scene (jerrycan found nearby, suspect's clothing...). While previous work has shown that it is possible to link two altered or unaltered ignitable liquids sharing a common source by source inference thanks to similarity calculation algorithm, it remains difficult to extend this to ignitable liquid residues in fire debris frequently received at the laboratory. In this work, we propose to study the contribution of matrices to the problem of source inference, using multivariate chemometric methods developed previously. The matrix chosen was clothing, little studied until now, but often found at fire scenes. The approach was then applied to a reduced sampling of unaltered gasoline and an undegraded matrix, followed by a substantial sampling of gasoline altered by evaporation on an undegraded matrix and then altered by combustion simultaneously on the same matrix. Evaluation of the results obtained validated the general hypothesis that it is possible to link weathered and unweathered gasoline samples, independently of the mode of weathering by evaporation or combustion and in the presence of matrix effects
Refai, Khalil. "Effet de la méso-architecture sur le comportement en fatigue des structures lattices optimisées obtenues par fabrication additive." Thesis, Paris, HESAM, 2020. http://www.theses.fr/2020HESAE028.
A numerical approach is proposed to assess the high cycle fatigue strength of periodic cellular structures produced by SLM under multiaxial loads. The model is based on a general numerical homogenisation scheme and an explicit description of the Elementary Cell combined to an extreme values analysis making use of a fatigue indicator parameter based on Crossland’s criterion. Also, geometric discrepancy and surface roughness are experimentally characterised and considered in the numerical model using three methods which are compared to the experimental fatigue strength. Topology optimisation (TO) pushes the boundaries of design freedom even further. In our study, Topology Optimisation was developed to prevent fatigue failure using SIMP method revisited and reformulated within the mathematical framework of Non-Uniform Rational BSpline functions
Virot, François. "Etude théorique de matériaux pour la spintronique." Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4816/document.
This thesis contains the scientific work of three years. The main topic can be defined as follows : study of electronic and magnetic properties of materials for spintronics. That technology of the future has still to find the necessary materials to realize new concepts. Our results are the following : We propose a new model to describe the magnetic configuration in thin ferromagnetic film with uniaxial anisotropy. It gives a better description of domain widths in function of film thickness and permits to obtain a good evaluation of the critical thickness where domains of Weiss type are no longer stable. The set of equations in reduced units is a useful tool to analyze experimental data. The ab-Initio study of diluted magnetic semiconductors has demonstrated the combined effect of strong correlations and Jahn-Teller distortion in (Ga,Mn)N and (Zn,Cr)S. The calculations confirm the experimental results of (Ga,Mn)N. We develop an analytical model that is complementary to the ab-Initio calculations and permits to create a link between several experimental parameters, the ab-Initio calculations and the former theory of Vallin. It has been used to interpret the optical measurements of (Zn,Cr)S. Our ab-Initio studies show that metacinnabar is a strong topological insulator with one peculiarity, it has a highly anisotropic Dirac cone. The passivation with hydrogen atoms influences the surface states of the topological insulator in the series HgX (X : S, Se, Te). When the dangling bonds are saturated by hydrogen, the trivial surface states disappear
Delplace, Pierre. "ÉTATS DE BORD ET CÔNES DE DIRAC DANS DES CRISTAUX BIDIMENSIONNELS." Phd thesis, Université Paris Sud - Paris XI, 2010. http://tel.archives-ouvertes.fr/tel-00607781.
Mostefaoui, Imene Meriem. "Analyse mathématique d’un système dynamique/réaction-diffusion modélisant la distribution des bactéries résistantes aux antibiotiques dans les rivières." Thesis, La Rochelle, 2014. http://www.theses.fr/2014LAROS020/document.
The objective of this thesis is the qualitative study of some models of the dynamic and the distribution of bacteria in a river. We are interested in the stability of equilibria and the existence of periodic solutions. The thesis can be divided into two parts; the first part is concerned with a mathematical analysis of a system of differential equations modelling the dynamics and the interactions of four species of bacteria in a river. The asymptotic behavior of equilibria is established. The stability study of equilibrium states is mainly done by construction of Lyapunov functions combined with LaSalle's invariance principle. On the other hand, the existence of periodic solutions is proved under certain conditions using the continuation theorem of Mawhin. In the second part of this thesis, we propose a non-autonomous convection-reaction diffusion system with nonlinear reaction source functions. This model refers to the quantification and the distribution of antibiotic resistant bacteria (ARB) in a river. Our main contributions are : (i) the determination of the limit set of the system; it is shown that it is reduced to the solutions of the associated elliptic system; (ii) sufficient conditions for the existence of a positive solution of the associated elliptic system based on the Leray Schauder's degree theory
Leriche, Raphaël. "Unconventional superconductivity in quasi-2D materials with strong spin-orbit coupling." Thesis, Sorbonne université, 2019. http://www.theses.fr/2019SORUS577.
The realization of topological superconductors is one of the main current goals of condensed matter physics. It was indeed predicted that such systems should host Majorana fermions. These Majorana fermions possess both a non-Abelian statistics and, because of their topological origin, a certain robustness against local disorder, which makes them attractive for quantum computing applications. One approach likely to lead to topological superconductivity consists in considering superconducting systems with strong spin-orbit coupling and with broken inversion symmetry. It is in this framework that, during this thesis, I performed scanning tunneling microscopy and spectroscopy measurements on quasi-2D materials : (LaSe)1,14(NbSe2)2 and Sr2IrO4. I first studied the electronic properties of misfit compound LaNb2Se5, which is a parent of transition metal dichalcogenide 2H-NbSe2. (LaSe)1,14(NbSe2)2 is a heterostructure made out of alternations of NbSe2 bilayers with trigonal prismatic geometry and LaSe bilayers with rocksalt structure. (LaSe)1,14(NbSe2)2 is a potential candidate for topological superconductivity because of the presence of both a strong spin-orbit coupling and of broken inversion symmetry in NbSe2 planes. Here, I present spectroscopic results showing that the electronic structure of(LaSe)1,14(NbSe2)2 is very similar to the one of electron-doped monolayer NbSe2 with a shift of the chemical potential of 0,3 eV, priorly never reached. I could also demonstrate the quasi- 2D nature of (LaSe)1,14(NbSe2)2 and more particularly the presence of a strong Ising spinorbit coupling. Moreover, the observed weakness of superconductivity against non-magnetic disorder combined with quasiparticle interferences measurements allowed me to exhibit the unconventional nature of (LaSe)1,14(NbSe2)2 superconducting order parameter. This study opens the possibility to use misfit heterostructures such as (LaSe)1,14(NbSe2)2 to study thephysics of transition metal dichalcogenides in the 2D limit, for which many theoretical studies predict topological superconductivity. In this thesis, I also present a study on the effects of doping on the electronic properties of iridate compound Sr2IrO4. Sr2IrO4 is a spin-orbit induced Mott insulator. Because inversion symmetry is locally broken in Sr2IrO4, some theoretical predictions suggest that Sr2IrO4 should turn into a topological superconductor once doped. Here, I exhibit a nanometer-scaleinhomogeneous doping-driven Mott insulator to pseudo-metallic phase transition. This work further justifies the importance of using a local probe such as scanning tunnelling microscopy in order to complete results on Mott physics obtained by integrative methods like angle-resolved photoemission spectroscopy
Pignol, Valérie. "Évolution et caractérisation de structures cellulaires bidimensionnelles expérimentales, en particulier les mousses de savon, et simulées." Phd thesis, Institut National Polytechnique de Lorraine - INPL, 1996. http://tel.archives-ouvertes.fr/tel-00717860.
Mallet, François. "COHERENCE QUANTIQUE, DIFUSION MAGNETIQUE ET EFFETS TOPOLOGIQUES." Phd thesis, 2006. http://tel.archives-ouvertes.fr/tel-00546850.
Müller, Roger Alexander. "Topological order in a broken-symmetry state." Thèse, 2015. http://hdl.handle.net/1866/12352.
Ung, Yvan. "Désintégration du faux vide médiée par des kinks en 1+1 dimensions." Thèse, 2015. http://hdl.handle.net/1866/12579.
In this thesis, we study the tunneling decay of the false vacuum, that is, a vacuum that is a relative minimum of a scalar potential. Topological defects in 1+1 dimension, called kinks, appear when the potential possesses a minimum that spontaneously breaks a discrete symmetry. In 3+1 dimensions, these kinks become domain walls. For instance, they appear in magnetic materials in condensed matter. A model with two coupled scalar fields will be studied, as well as the solutions to the equations of motion that arise from it. We will then analyze how the energy of the static solutions depend on the parameters of the model. A numerical survey of parameter space reveals that the stable solutions are located between dissociation zones, areas in parameter space where stable solutions no longer exist. The behavior of the unstable solutions in the dissociation zones can be very different depending on which dissociation zone a solution is found near the dissociation zone. The potential first consists in a sixth-order polynomial, to which is added a quartic polynomial multiplied by a coupling term, and is chosen such that the extremities of the kink are at distinct false vacua. The decay rate has been estimated by a semiclassical approximation to show the impact of topological defects on the stability of the false vacuum. The project consists in determining the conditions that allow the kinks to catalyze false vacuum decay. It appears that we found an expression for the critical kink density and that we understand what happens with most terms.