<p dir="ltr"><b>Tellurium (Te) stands out as an elemental narrow-bandgap semiconductor characterized by its distinctive chiral crystal structure. The interplay between fundamental symmetries and the topological properties of electrons has garnered significant attention in the scientific community. With its unique chiral crystal structure featuring three Tellurium atoms spiraling within a single unit cell, Tellurium offers a singular material system. This system provides an exceptional opportunity to explore the novel quantum and topological transport properties of electrons. Hydrothermally grown two-dimensional (2D) Te with a thickness of several nanometers gives us an opportunity to precisely control the carrier density and the carrier type in Te using gate voltage. In this dissertation, the spin-orbit coupling (SOC) of Te is quantitatively analyzed using the weak anti-localization effect. The strong SOC also gives rise to the Weyl point at the band edge of the conduction band. The topological nontrivial band structure of Te is characterized by a π phase shift in the Shubnikov-de Haas (SdH) oscillations. Due to the high mobility, the quantum Hall effect is measured with low spin and valley Landau levels controlled by an electric and magnetic field. Bilayer charge transferable quantum Hall states of Weyl fermions is observed in a wide Te quantum well. The topological phase transition from a semiconductor to Weyl semimetal under high pressure is studied up to 2.47 GPa. The chirality of 2D Te is separated by the hot sulfuric acid etching technique. The spin configuration and topological charge of the Weyl node exhibit a reversal in different chiralities, leading to an inverse in nonlinear responses, encompassing both electrical (nonreciprocal transport in the longitudinal direction and nonlinear planar Hall effect in the transvers direction) and optical phenomena (circular photogalvanic effect and circular photovoltaic effect). Our results unveil the topological nature of the Tellurium (Te) band structures, offering a promising avenue for controlling charge and spin transport within the chiral degree of freedom.</b></p>

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal. / Des creux d’interférence sont fréquemment observés dans les spectres d’absorption de complexes d’éléments de transition. Ces creux résultent de l’interaction entre des états électroniques excités de multiplicité de spin différente. Un modèle de puits de potentiel couplés pour les états électroniques est nécessaire pour l’analyse des spectres d’absorption. Une équation analytique, dérivée de ce modèle, permet de calculer les spectres d’absorption non-résolus. L’impact d’une variation de chaque paramètre sur l’allure des spectres calculés est présenté. Le calcul avec l’équation analytique de spectres d’absorption peu résolus de complexes du nickel(II) de coordination octaédrique reproduit bien la région du maximum de la bande et du creux. Les paramètres obtenus sont quantitatifs et ont une signification physique. Le modèle est aussi employé pour l’analyse des spectres avec des progressions vibroniques résolues, mais dont les différences entre progressions sont non-constantes. Les calculs numériques exacts reproduisent bien les écarts entre les maxima des progressions et leur intensité. / Interference dips are often observed in absorption spectra of transition metal complexes. These dips resuit from the interaction between excited states with different spin multiplicities. A mode! of coupled potential wells for the electronic states is required to analyse the absorption spectra. The pararneters of an analytical equation derived from this modet are varied individually. The analytical equation is used to calculate the unresolved absorption spectra of octahedral nickel(II) complexes. The calculated spectra reproduce well the experimental ones, especially in the regions of the dip and of the maximum of the band. The values for the parameters ohtained from the equation are physically relevant, quantitative and give precise information on excited-state properties for the complexes studied. Numerical calculations of absorption spectra showing resolved progressions with nonconstant energy intervals are done with the model and reproduce well the intervals between the maxima of the progression and their intensities.

<p dir="ltr">InSbAs is a promising platform for exploring topological superconductivity and spin-based device applications, thanks to its strong spin-orbit coupling (SOC) and high effective <i>g</i>-factor. This thesis investigates low-temperature transport of electrons confined in InSb_1-xAs_x quantum wells. Specifically, we study the properties of electrons confined in 2D and 0D by fabricating gated Hall bars and gate-defined quantum dots. Theoretical considerations suggest that InSbAs will have stronger SOC and a larger effective <i>g</i>-factor compared to InAs and InSb. Both the SOC and effective <i>g</i>-factor change as a function of arsenic mole fraction, but much remains to be understood in real material systems. Here, we study the dominant scattering mechanisms, effective mass, spin-orbit coupling strength, and the <i>g</i>-factor in InSb_1-xAs_x quantum wells grown by molecular beam epitaxy. </p><p dir="ltr">We explore 30 nm InSb_1-xAs_x quantum wells with arsenic mole fractions of <i>x</i> = 0.05, 0.13, and 0.19. The 2DEG properties were studied by fabricating gated Hall bars and placing them in a perpendicular magnetic field at low temperatures (T = 10 - 300 mK). All samples showed high-quality transport with mobility greater than 100,000 cm²/Vs. For the <i>x</i> = 0.05 sample, the 2DEG displays a peak mobility μ = 2.4 x 10⁵ cm²/Vs at a density of <i>n</i> = 2.5 x 10¹¹ cm^-². We investigated the evolution of mobility as a function of arsenic mole fraction and 2DEG density for all samples. As the arsenic mole fraction increases, peak mobility decreases, and the dependence of mobility on density becomes weaker, suggesting that short-range scattering becomes the dominant scattering mechanism. We extracted an alloy scattering rate of τ_alloy = 45 ns^-1 per % As, an important parameter for understanding the impact of disorder on induced superconductivity. The high mobility, strong spin-orbit coupling, and low effective mass in this material system resulted in a beating pattern in the Shubnikov de Haas oscillations, allowing for the extraction of the Rashba parameter as a function of density and arsenic mole fraction. We observed a gate tunable spin-orbit coupling and, as predicted by theory, an increase in spin-orbit coupling with increasing arsenic mole fraction. For the sample with x = 0.19, the highest Rashba parameter is α_R ~ 300 meVÅ, which is significantly higher than in InSb. </p><p dir="ltr">In addition, we explored 0D confinement by fabricating a gate-defined quantum dot in an InSb₀_.87As_0.13 quantum well. By studying the evolution of Coulomb blockade peaks and differential conductance peaks as a function of magnetic field, a nearly isotropic in-plane effective <i>g</i>-factor in the [1-10] and [110] crystallographic directions was extracted, ranging from 49-58. The values extracted are 1.8 times higher than in a quantum dot fabricated in pure InSb. Furthermore, this study produced the first demonstration of a tunable spin-orbit coupling in this material system. This was achieved by measuring the avoided crossing gap, mediated by spin-orbit coupling, between the ground state and excited state in a magnetic field. The avoided crossing gap indicates the strength of the spin-orbit coupling; the maximum energy separation extracted is Δ_SO ~100 μeV. </p><p dir="ltr">Our work should stimulate further investigation of InSbAs quantum wells as a promising platform for applications requiring strong spin-orbit coupling, such as topological superconductivity or spin-based devices.</p>

No description available.

No description available.

Low-temperature weak-localization (WL) and antilocalization (AL) magnetotransport measurements are sensitive to electron interference, and thus can be used as a probe of quantum states. The spin-dependent interactions between controllable surface magnetism and itinerant electrons in a non-magnetic host provide insight for spin-based technologies, magnetic data storage and quantum information processing. This dissertation studies two different host systems, an In$_{0.53}$Ga$_{0.47}$As quantum well at a distance from the surface of a heterostructure, and an accumulation layer on an InAs surface. Both the systems are two-dimensional electron systems (2DESs), and possess prominent Rashba spin-orbit interaction caused by structural inversion asymmetry, which meets the prerequisites for AL. The surface local moments influence the surrounding electrons in two ways, increasing their spin-orbit scattering, and inducing magnetic spin-flip scattering, which carries information about magnetic interactions. The two effects modify the AL signals in opposing directions: the spin-flip scattering of electrons shrinks the signal, and requires a close proximity to the species, whereas the increase of spin-orbit scattering broadens and increases the signal. Accordingly, we only observe an increase in spin-orbit scattering in the study of the interactions between ferromagnetic Co$_{0.6}$Fe$_{0.4}$ nanopillars and the relatively distant InGaAs quantum well. With these CoFe nanopillars, a decrease in spin decoherence time is observed, attributed to the spatially varying magnetic field from the local moments. A good agreement between the data and a theoretical calculation suggests that the CoFe nanopillars also generate an appreciable average magnetic field normal to the surface, of value $\sim$ 35 G. We also performed a series of comparative AL measurements to experimentally investigate the interactions and spin-exchange between InAs surface accumulation electrons and local magnetic moments of rare earth ions Sm$^{3+}$, Gd$^{3+}$, Ho$^{3+}$, of transition metal ions Ni$^{2+}$, Co$^{2+}$, and Fe$^{3+}$, and of Ni$^{2+}$-, Co$^{2+}$-, and Fe$^{3+}$-phthalocyanines deposited on the surface. The deposited species generate magnetic scattering with magnitude dependent on their electron configurations and effective moments. Particularly for Fe$^{3+}$, the significant spin-flip scattering due to the outermost 3d shell and the fairly high magnetic moments modifies the AL signal into a WL signal. Experiments indicate a temperature-independent magnetic spin-flip scattering for most of the species except for Ho$^{3+}$ and Co$^{2+}$. Ho$^{3+}$ yields electron spin-flip rates proportional to the square root of temperature, resulting from transitions between closely spaced energy levels of spin-orbit multiplets. In the case of Co$^{2+}$, either a spin crossover or a spin-glass system forms, and hence spin-flip rates transit between two saturation regions as temperature varies. Concerning the spin-orbit scattering rate, we observe an increase for all the species, and the increase is correlated with the effective electric fields produced by the species. In both 2DESs, the inelastic time is inversely proportional to temperature, consistent with phase decoherence via the Nyquist mechanism. Our method provides a controlled way to probe the quantum spin interactions of 2DESs, either in a quantum well, or on the surface of InAs. / Ph. D.

Tesis por compendio / [ES] Al igual que la masa o la carga, el espín es una propiedad física fundamental que, típicamente, aparece en la descripción de los sistemas cuánticos. Más allá de sus importantes implicaciones teóricas, el creciente avance de la tecnología y el desarrollo de los dispositivos hacia escalas cada vez más pequeñas ha favorecido el surgimiento de multitud de aplicaciones que involucran al espín, entre las cuales se destaca la espintrónica; una nueva forma de electrónica en la que, además de la carga, también se explotan los grados de libertad otorgados por el espín del electrón. Por supuesto, el espín no es exclusivo de los electrones, está presente en todas las partículas elementales, y por ende, en los fotones. En este caso, y a diferencia de lo que ocurre con los electrones, existe una correspondencia clásica que relaciona el espín del fotón con los estados de polarización circular de la luz. Por lo tanto, en nano-óptica y en fotónica, los fenómenos basados en el espín se refieren, grosso modo, a aquellos que son fuertemente dependientes de la polarización circular de la luz. En este marco general, uno de los ejemplos más preponderantes se halla en la interacción espín-órbita. En su versión óptica establece que, bajo ciertas condiciones, es posible que exista una influencia mutua entre el estado de polarización (espín) y la propagación (órbita) de la luz. A pesar de su carácter ubicuo en todos los procesos ópticos básicos, sus efectos son muy débiles, y su manifestación se restringe a la nanoescala, lo cual dificulta su observación e identificación. En este mismo contexto, otro concepto heredado del formalismo cuántico que tiene análogo fotónico directo es la quiralidad óptica; una propiedad dinámica local que, de alguna manera, permite cuantificar escalarmente el espín de un campo óptico. Aparte de su controvertido significado físico y su estrecho vínculo con los sistemas plasmónicos y los metamateriales, como amplificadores de sus efectos, su principal característica fundamental es que, para los campos ópticos en el vacío, es una cantidad conservada. En esta tesis se ahonda teóricamente en los fundamentos básicos de estas características fotónicas. Específicamente, se demuestra analíticamente que la interacción espín-órbita es un fenómeno que surge natural y necesariamente en la nanoescala. Sobre esta base se expone un formalismo para extender la excitación unidireccional de campo cercano más allá de la aproximación dipolar, lo cual facilita su observación y mejora las propiedades de acoplo. Por otra parte, se analiza el concepto de la quiralidad óptica, originalmente definida en el vacío, y se generaliza a cualquier tipo de medio, incluyendo sistemas altamente dispersivos. Asimismo, se exploran diferentes configuraciones que permitan implementar las principales funcionalidades quirópticas (sensado y espectroscopía) en plataformas de fotónica integrada. Además de su potencial para aplicaciones, este estudio tiende un puente para abordar clásicamente propiedades y efectos que tradicionalmente son de tipo cuántico. / [CA] Igual que la massa o la càrrega, l'espín és una propietat física fonamental que, típicament, apareix en la descripció dels sistemes quàntics. Més enllà de les seves importants implicacions teòriques, el creixent avanç de la tecnologia i el desenvolupament dels dispositius cap a escales cada vegada més petites ha afavorit el sorgiment de multitud d'aplicacions que involucren l'espín, entre les quals es destaca l'espintrònica; una nova forma d'electrònica en què, a més de la càrrega, també s'exploten els graus de llibertat atorgats per l'espín de l'electró. Per descomptat, l'espín no és exclusiu dels electrons, és present en totes les partícules elementals, i per tant, en els fotons. En aquest cas, i a diferència del que passa amb els electrons, hi ha una correspondència clàssica que relaciona l'espín del fotó amb els estats de polarització circular de la llum. Per tant, en nano-òptica i en fotònica, els fenòmens basats en l'espín es refereixen, grosso modo, a aquells que són fortament dependents de la polarització circular de la llum. En aquest marc general, un dels exemples més preponderants es troba en la interacció espín-òrbita. En la seva versió òptica estableix que, sota certes condicions, és possible que hi hagi una influència mútua entre l'estat de polarització (espín) i la propagació (òrbita) de la llum. Malgrat el seu caràcter ubic en tots els processos òptics bàsics, els seus efectes són molt febles, i la seva manifestació es restringeix a la nanoescala, la qual cosa dificulta la seva observació i identificació. En aquest mateix context, un altre concepte heretat del formalisme quàntic que té anàleg fotònic directe és la quiralitat òptica; una propietat dinàmica local que, d'alguna manera, quantifica escalarment l'espín d'un camp òptic. A banda del seu controvertit significat físic i el seu estret vincle amb els sistemes plasmònics i els metamaterials, com amplificadors dels seus efectes, la seva principal característica fonamental és que, per als camps òptics en el buit, és una quantitat conservada. Des d'un enfocament teòric, aquesta tesi aprofundeix en els fonaments bàsics d'aquestes característiques fotòniques. Específicament, es demostra analíticament que la interacció espín-òrbita és un fenomen que sorgeix natural i necessàriament en la nanoescala. Sobre aquesta base s'exposa un formalisme per estendre l'efecte d'excitació unidireccional de camp pròxim més enllà de l'aproximació dipolar, la qual cosa facilita la seva observació i millora les propietats d'acoblo. D'altra banda, s'analitza el concepte de la quiralitat òptica, originalment definida en el buit, i es generalitza a qualsevol tipus de mitjà, incloent sistemes altament dispersius. Així mateix, s'exploren diferents configuracions que permetin implementar les principals funcionalitats quiròptiques (sensat i espectroscòpia) en plataformes de fotònica integrada. A més del seu potencial per a aplicacions, aquest estudi tendeix un pont per abordar clàssicament propietats i efectes tradicionalment quàntics. / [EN] Just like mass or charge, spin is a fundamental physical property that, typically, appears in the description of quantum systems. Beyond its important theoretical implications, the rapid advance of technology along with the relentless trend toward the development of devices at increasingly smaller scales have boosted the occurrence of a wide range of applications involving spin, among which is highlighted the spintronics; a novel form of electronics which, besides the charge, also exploits the degrees of freedom provided by the electron spin. Of course, the spin is not exclusive to electrons, but is actually present in all the elementary particles, and therefore in photons. In such a case, and unlike what happens with electrons, there exists a direct classical correspondence relating the spin of photons with the circular polarization states of light. Thus, in nano-optics and photonics, spin-dependent phenomena are broadly referred to as those that strongly rely upon the circular polarization of light. Within this general framework, one of the most preponderant examples is found in the spin-orbit interaction. In its optical version, it states that, under certain conditions, it is possible that there exists a mutual influence between the state of polarization (spin) and the propagation (orbit) of light. Despite its ubiquitous character in all basic optical processes, its effects are very weak, and its manifestation is restricted at the nanoscale, thereby hindering its observation and identification. In this same context, another concept somehow inherited from the quantum formalism with a direct photonic analogue is the optical chirality; a local dynamical property that, in a way, allows one to quantifying scalarly the spin of an optical field. Apart from its controversial physical meaning and its close relationship with plasmonic systems and metamaterials, often regarded as chiral enhancers, its main feature is that, for optical fields in the vacuum, it is a conserved quantity. From a theoretical standpoint, this thesis delves into the basics of these photonic traits. Specifically, it is analytically demonstrated that the spin-orbit interaction is indeed a phenomenon that naturally and necessarily emerges at the nanoscale. Building on this, it is addressed a formalism to extend the effect of near-field unidirectional excitation beyond the dipolar approximation, thus facilitating its observation and improving the coupling performance. On the other side, the optical chirality, originally put forward for electromagnetic fields in vacuum, is thoroughly analyzed and generalized to any arbitrary medium, including highly dispersive systems. Furthermore, different configurations for implementing the main chiroptical functionalities (sensing and spectroscopy) in integrated photonic platforms are explored. Besides its potential for applications, this study lays a bridge to classically approach features and effects which are traditionally quantum-like. / This work was supported by fundings from Ministerio de Economía y Competitividad of Spain (MINECO) under Contract No.TEC2014-51902-C2-1-R. and by ERC Starting Grant No. ERC-2016-STG-714151-PSINFONI. This work was also partially supported by funding from the European Commission Project THOR H2020-EU-829067. / Vázquez Lozano, JE. (2021). Spin-Dependent Optical Phenomena: Fundamentals and Applications [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/166775 / Compendio

In the context of the search and tuning for novel magnetic materials, transition metal compounds exhibit remarkable features where the spin-orbit interaction is crucial. The collective interactions between various effects, like spins and charges, create different classes of unique magnetic systems. For heavy transition-metal compounds, the strength of spin-orbital coupling is enhanced. The jeff. = 1/2 Mott insulating state emerges from the combination of the spin-orbit interaction and the electronic correlations. The quantum-chemistry methods are employed in this thesis to investigate single- and two-site magnetic interactions of the selected transition-metal compounds. We also provide different estimations for the single- and two-site magnetic interactions based on the level of calculation accuracy. In this thesis, we apply ab initio quantum-chemistry methods to explore the electronic and magnetic properties of several d/f compounds. The thesis structure is as follows: In Chapter 1, the introduction of the thesis provides a short discussion of the electronic correlations and magnetism in transition metal compounds. In Chapter 2, the fundamentals of the quantum chemistry wavefunction-based approach are covered. This chapter gives an overview of the applied methods in this thesis. In Chapter 3, we discuss the quantum chemistry approach to investigate the material candidates to host Kitaev physics. The technique to obtain the strength of two-site magnetic couplings, including the Kitaev coupling, is discussed in-depth. In Chapter 4, we apply the technique, which is described in Chapter 3, to investigate the two-site magnetic interactions in the H3LiIr2O6, and Cu2IrO2 compounds as Kitaev candidates. The two-site magnetic couplings are reported in these compounds. In Chapter 5, we use quantum chemistry methods to investigate the on-site electronic and magnetic properties in the KCeO2 compound where 4f1 Ce3+ ions form a triangular two-dimensional lattice with sites of effective spin-1/2. Similar ytterbiumbased delafossites had been investigated as candidates for quantum spin liquid ground states. The absence of ordinary magnetic order is characteristic of quantum spinliquid states where quantum entanglements and fractionalized excitations are enriched. In Chapter 6, the magnetic properties of Co 3d8 ions doped in the Li3N crystalline solid are discussed. The results of the quantum chemistry investigation are been set side by side along with the experiment’s results. The Co ion in such a rare environment gives rise to single-site magnetism of an easy-plane anisotropy.:Table of Contents . . . . . . . . . . . . . . . . . . . . . . iv List of Figures . . . . . . . . . . . . . . . . . . . . . . . . .vi Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .i Acknowledgements . . . . . . . . . . . . . . . . . . . . . .iii 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 1.1 Electronic correlations and magnetism in transition metal compounds ...........1 1.2 Thesis outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2 Quantum chemistry methodology . . . . . . . . . . . . . . . . .6 2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.2 Many-electron Hartree-Fock approximation . . . . . . . . . . . . . . . 9 2.3 Multi-configurational self-consistent field and multi-reference configuration methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 2.4 Spin-orbit interaction and g-factors calculation . . . . . . . . . . . . . 15 2.5 Embedded cluster approach . . . . . . . . . . . . . . . . . . . . . . . 18 2.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 3 Quantum chemistry investigation of Kitaev material candidates . . . . . . . . . . .21 3.1 Introduction to the Kitaev model . . . . . . . . . . . . . . . . . . . . 23 3.2 Kitaev materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 3.3 Two-site quantum chemistry calculations . . . . . . . . . . . . . . . . 36 3.4 Effective Model of Two Spin-1/2 . . . . . . . . . . . . . . . . . . . . . 38 3.5 Non-canonical correspondence between two-site QC results and the effective Hamiltonian . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 3.6 Pseudospin coordinate system and canonical correspondence between two-site QC results and the effective Hamiltonian . . . . . . . . . . . 51 3.7 Signs of the g-tensor in the Kitaev limit . . . . . . . . . . . . . . . . 53 3.8 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 4 Kitaev material candidates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .60 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 4.2 Details of QC calculations . . . . . . . . . . . . . . . . . . . . . . . . 64 4.3 QC investigation of H3LiIr2O6 . . . . . . . . . . . . . . . . . . . . . . 66 4.4 QC investigation of Cu2IrO3 . . . . . . . . . . . . . . . . . . . . . . . 75 4.5 Impact of local symmetries on the obtained sets of magnetic couplings ......... 82 4.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 5 Ce ions in two-dimensional triangular spin-1/2 lattices . . . . . . . . . . . . . . . . . . . . 89 5.1 Spin-1/2 frustrated triangular lattice . . . . . . . . . . . . . . . . . . 90 5.2 Correlated 4f -compounds as frustrated triangular lattices . . . . . . 94 5.3 Crystal structure of KCeO2 . . . . . . . . . . . . . . . . . . . . . . . 95 5.4 QC results for the electronic structure of Ce3+ ions in KCeO2 . . . . 100 5.5 The competition of SOC and crystal field splittings in KCeO2 . . . . 102 5.6 Chapter summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 6 Co-ion substitutes with linear coordination in Li3N . . . . . . . . . . . . . . . . . . . . . . 109 6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 6.2 Crystal structure of Li2(Li(1−x)Cox)N and spectroscopic measurements .......112 6.3 QC computational details . . . . . . . . . . . . . . . . . . . . . . . . 115 6.4 Ab initio QC investigation of the Co+ 3d8 electronic structure doped into Li3N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 6.5 Chapter summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .135

Dans une première partie nous explorerons les effets d'impuretés désordonnées et paramagnétiques sur l'effet spin-Hall intrinsèque dans un gaz d'électrons bi-dimensionnel avec un couplage spin-orbite de Rashba. A faible désordre, la conductivité de spin-Hall reste proche de sa valeur d'échantillon pur, comme le montrent un calcul analytique de réponse linéaire et une étude numérique. De fortes fluctuations sont toutefois observées, elles augmentent avec l'importance du désordre. Pour caractériser la dynamique d'un paquet d'onde sur un réseau, nous mesurons sa taille, le taux de participation inverse, et sa dimension de corrélation. Le système subit une transition de localisation à une valeur critique du désordre. Dans le régime localisé, la densité locale d'états n'est plus uniforme et ne coïncide plus avec la densité totale d'états. Une corrélation antiferromagnétique entre les impuretés et les électrons de conduction est observée. Après la transition de localisation, la conductivité de spin augmente significativement. La première correction quantique dans le formalisme de réponse linéaire, contribue positivement à la conductivité de spin-Hall. Dans une seconde partie, le modèle de Hubbard avec double échange avec corrélations électroniques est étudié par la méthode du champ moyen dynamique (DMFT) dans l'approximation de non-croisement pour la résolution du problème d'impureté (NCA). Autour du quart remplissage, un polaron orbital est observé et décrit à l'aide d'un Hamiltonien effectif. Le double échange dans les semi-conducteurs magnétiques dilués est étudié dans l'approximation du potentiel cohérent (CPA). / Spintronics is a research area that is concerned with the storage and transfer of information by means of electron spins. In the first part we investigated the intrinsic spin Hall effect in the presence of disordered magnetic impurities in a paramagnetic state in a two dimensional electron gas with Rashba spin-orbit coupling. In the presence of weak magnetic disorder the spin Hall conductivity stays close to its universal (clean system) value, as shown by analytical linear response calculations and numerical simulations. Heavy spin conductivity fluctuations are observed, that increase with disorder strength. To investigate the spreading of a wavepacket on a lattice we measure the wavepacket width, the inverse participation ratio and the (2)-fractal dimension. It is shown the system undergoes a localization transition at a critical disorder strength. In the localized regime the local density of states is not uniform anymore. An anti-ferromagnetic correlation between electron spins and impurity magnetic moments is observed. Beyond the localization transition the spin conductivity increases significantly. The first quantum (Cooperon) corrections in the linear response formalism are shown to contribute positively to the spin Hall conductivity. In the second part the double exchange Hubbard model for correlated electron systems is studied using dynamical mean field theory (DMFT) with the non-crossing approximation (NCA). Around quarter filling an orbital polaron is observed, numerically and in an effective Hamiltonian. Double exchange in dilute magnetic semiconductors is studied using the coherent potential approximation (CPA).

Quantum computers are appealing for their ability to solve some tasks much faster than their classical counterparts. In fact, they have a potential to perform the full configuration interaction (FCI) energy calculations with a polynomial scaling only. This is in contrast to con- ventional computers where FCI scales exponentially. We provide a detailed description of the quantum version of the FCI method and the results of numerical simulations of the ground and excited state energy calculations of the methylene molecule. We further generalize this method to the relativistic four component regime and show how to efficiently solve the eigenproblem of the Dirac-Coulomb(-Breit) Hamiltonian on a quantum computer. We demonstrate the func- tionality of the proposed procedure by numerical simulations of computations of the spin-orbit splitting in the SbH molecule. Finally, we propose quantum circuits with 3 qubits and 9 or 10 CNOTs, which implement a proof-of-principle relativistic quantum chemical calculation for this molecule and might be suitable for an experimental realization. 1