The quantum interference effects, such as the Autler-Townes (AT) effect and electromagnetically induced transparency (EIT) applied to molecular systems are the focus of this Dissertation in the context of high resolution molecular spectroscopy. We demonstrate that the AT effect can be used to manipulate the spin character of a spin-orbit coupled pair of molecular energy levels serving as a \textit{gateway} between the singlet and triplet electronic states. We demonstrate that the singlet-triplet mixing characters of the \textit{gateway} levels can be controlled by manipulating the coupling laser \textit{E} field amplitude. We observe experimentally the collisional population transfer between electronic states $G^1\Pi_g (v=12, J=21, f)$ and $1^3\Sigma _g^-(v=1, N=21, f)$ of $^7$Li$_2$. We obtain the Stern-Vollmer plot according to the vapor pressure dependence of collisional transfer rate. The triplet fluorescence from the mixed \textit{gateway} levels to the triplet $b^3\Pi_u(v'=1,J'= / Physics

The ultimate goal in the rapidly burgeoning field of spintronics is to realize semiconductor-based devices that utilize the spin degree of freedom of a single charge carrier (electron or hole) or an ensemble of such carriers to achieve novel and/or enhanced device functionalities such as spin based light emitting devices, spin transistors and femto-Tesla magnetic field sensors. These devices share a common feature: they all rely on controlled transport of spins in semiconductors. A prototypical spintronic device has a transistor-like configuration in which a semiconducting channel is sandwiched between two contacts (source and drain) with a gate electrode sitting on top of the channel. Unlike conventional charge-based transistors, the source electrode of a spin transistor is a ferromagnetic (or half-metallic) material which injects spin polarized electrons in the channel. During transit, the spin polarizations of the electrons are controllably rotated by a gate electric field mediated spin-orbit coupling effect. The drain contact is ferromagnetic (or half-metallic) as well and the transmission probability of an electron through this drain electrode depends on the relative orientation of electron spin polarization and the (fixed) magnetization of the drain. When the spins of the electrons are parallel to the drain magnetization, they are transmitted by the drain resulting in a large device current (ON state of spin FET). However, these electrons will be completely blocked if their spins are antiparallel to the drain magnetization, and ideally, in this situation device current will be zero (OFF state of spinFET). Thus, if we vary the gate voltage, we can modulate the channel current by controlling the spin orientations of the electrons with respect to the drain magnetization. This is how transistor action is realized (Datta-Das model). However, during transport, electrons' velocities change randomly with time due to scattering and hence different electrons experience different spin-orbit magnetic fields. As a result, even though all electrons start their journey with identical spin orientations, soon after injection spins of different electrons point along different directions in space. This randomization of initial spin polarization is referred to as spin relaxation and this is detrimental to the spintronic devices. In particular, for Datta-Das transistor, this will lead to inefficient gate control and large leakage current in the OFF state of the spinFET. The aim of this work is to understand various spin relaxation processes that are operative in semiconductor nanostructures and to indicate possible ways of minimizing them. The theoretical aspect of this work (Chapters 2-5) focuses on the D'yakonov-Perel' process of spin relaxation in a semiconductor quantum wire. This process of spin relaxation occurs because during transport electron spin precesses like a spinning top about the spin-orbit magnetic field. We show that the conventional drift-diffusion model of spin transport, which has been used extensively in literature, completely breaks down in case of a quantum confined system (e.g. a quantum wire). Our approach employs a semi-classical model which couples the spin density matrix evolution with the Boltzmann transport equation. Using this model we have thoroughly studied spin relaxation in a semiconductor quantum wire and identified several inconsistencies of the drift-diffusion formalism.The experimental side of this work (Chapters 6-8) deals with two different issues: (a) performing spin transport experiments in order to extract spin relaxation length and time in various materials (e.g. Cu, Alq3) under one-dimensional confinement, and (b) measurement of the ensemble spin dephasing time in self-assembled cadmium sulfide quantum dots using electron spin resonance technique. The spin transport experiment, as described in Chapter 7 of this dissertation, shows that the spin relaxation time in organic semiconductor (Alq3) is extremely long, approaching a few seconds at low temperatures. Alq3 is the chemical formula of tris- 8 hydroxy-quinoline aluminum, which is a small molecular weight organic semiconductor. This material is extensively used in organic display industry as the electron transport and emission layer in green organic light emitting diodes. The long spin relaxation time in Alq3 makes it an ideal platform for spintronics. This also indicates that it may be possible to realize spin based organic light emitting diodes which will have much higher internal quantum efficiency than their conventional non-spin counterparts. From spin transport experiments mentioned above we have also identified Elliott-Yafet mode as the dominant spin relaxation mechanism operative in organic semiconductors. Electron spin resonance experiment performed on self-assembled quantum dots (Chapter 8) allows us to determine the ensemble spin dephasing time (or transverse spin relaxation time) of electrons confined in these systems. In quantum dots electrons are strongly localized in space. Surprisingly, the ensemble spin dephasing time shows an increasing trend as we increase temperature. The most likely explanation for this phenomenon is that spin dephasing in quantum dots (unlike quantum wells and wires) is dominated by nuclear hyperfine interaction, which weakens progressively with temperature. We hope that our work, which elaborates on all of the above mentioned topics in great detail, will be a significant contribution towards the current state of knowledge of subtle spin-based issues operative in nanoscale device structures, and will ultimately lead to realization of novel nano-spintronic devices.

L'état supraconducteur étant un condensat de paires de Cooper constitué d'électrons de moments et de spins opposés, il peut être fortement influencé par des effets de spin. Au cours de cette thèse, nous étudions l'effet d'un fort champ d'échange et d'un effet spin-orbite de type Rashba sur les propriétés supraconductrices. Dans une première partie, on étudie les effets associés à l'interaction entre supraconductivité et fort champ d'échange, se caractérisant par une transition de phase vers un état supraconducteur inhomogène découvert par Fulde, Ferrell, Larkin et Ovchinnikov (FFLO). On étudie tout particulièrement les fluctuations supraconductrices à l'approche de la transition de phase. On montre que ces fluctuations peuvent servir de révélateur à cette phase. Notamment, la capacité calorifique et la paraconductivité divergent de façon caractéristique à la transition vers un état modulé. On décrit également comment les effets paramagnétiques modifient les fluctuations de l'aimantation, annulant la réponse diamagnétique ou produisant des oscillations entre réponse para- et dia-magnétique. La seconde partie est dévolue aux jonctions supraconducteur-ferromagnétique (S/F). Dans les jonctions Josephson S/F/S, le champ d'échange donne lieu à des oscillations du courant critique en fonction de la longueur de la jonction, charactérisées par une alternance des états 0 et . On prédit une transition entre les états 0 et induite par la température, même dans la limite ballistique. Dans cette limite ballistique, on montre également que le courant de Josephson s'atténu sous la forme de lois de puissance en fonction de la longueur de la jonction, alors que le cas diffusif présente une atténuation exponentielle. On étudie ensuite la seconde harmonique de la relation courant-phase en présence d'une faible quantité d'impuretés. La dernière partie traite des effets de proximité lorsque les deux effets paramagnétique et spin-orbite sont présents dans une jonction Josephson. On montre que l'association d'une interaction Rashba et d'un champ d'échange induit un couplage direct entre les ordres magnétique et supraconducteur. En particulier, ce couplage permet de générer toute la dynamique magnétique par l'application d'une simple tension électrique. / The superconducting state being a Cooper pair condensate built on opposite spin and momentum electrons, it can be strongly influenced by any spin effect. In this thesis, we investigate the roles of strong paramagnetic and spin-orbit effects on superconducting properties. In a first part, the interplay between paramagnetic effect and bulk superconductivity is studied, leading to the modulated Fulde, Ferrell, Larkin and Ovchinnikov phase (FFLO phase). We focus on superconducting fluctuations near to the FFLO state. We show that these fluctuations can serve as a smoking gun for this phase. Noticeably, the fluctuation heat capacity and paraconductivity diverge in a characteristic way when approaching the phase transition towards a modulated state. Moreover, the fluctuation induced magnetization is predicted to be drastically quenched or to oscillate between dia- and para-magnetic responses. The second part is devoted to superconductor-ferromagnetic (S/F) junctions. In S/F/S Josephson junctions, the exchange field is responsible for the critical current oscillation, characterized by alternative 0- and -states, with respect to the junction length. We predict a temperature induced (0-) state transition, even in the ballistic case. Moreover, the ballistic case exhibits some power law decays of the Josephson current, in contrast to the exponentially decaying current in dirty limit. The moderately dirty limit is then investigated, and the second harmonic of the current-phase relation is established. The last part deals with proximity effects when both paramagnetic and spin-orbit interactions are present in a Josephson junction. We show that the association of both Rashba interaction and exchange field induces a direct coupling between magnetic and superconducting orders. Particularly, this coupling generates the complete magnetization dynamics by applying an appropriate d.c. voltage.

Title: Relativistic Theory of Electron Transport in Magnetic Layers Author: Rudolf Sýkora Department / Institute: Institude of Theoretical Physics Supervisor of the doctoral thesis: doc. RNDr. Ilja Turek, DrSc., Department of Condensed Matter Physics Abstract: We review the density-functional theory (DFT) in detail using the Levy Lieb ap- proach. The Kohn Sham scheme is discussed, starting from the simplest spinless non- relativistic case, then including spin and considering potential spin magnetism, and finally deriv- ing the full Kohn Sham Dirac relativistic scheme. The Linear Muffin-Tin Orbital (LMTO) method for electronic-structure calculation is presented, together with mentioning the necessary changes to include the spin-orbit (SO) interaction effects to an otherwise scalar-relativistic (SR) theory. Derivation of an electronic-conductance formula for a layered system is given, based on the Landauer scattering picture and using simple non-equilibrium Green functions. The formal- ism is applied to layered metallic systems of light elements Co, Ni, Cu elements, and to layered systems with a tunnelling barrier, Fe/MgO/Ag and Fe/GaAs/Ag. The effects of the SO interac- tion on the Giant Magnetoresistance (GMR) ratio and/or the Tunnelling Anisotropy Magnetore- sistance (TAMR) for these systems are discussed....

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

Ma thèse est consacrée aux nouveaux phénomènes nano-optiques et aux dispositifs basés sur l'interaction spin-orbite de la lumière (SOI). Tout d'abord, il a été démontré un SOI uniquement piloté par le champ magnétique de la lumière permettant de diriger avec précision les ondes de surface de Bloch, offrant ainsi une nouvelle manifestation du champ magnétique optique. Ensuite, nous avons proposé et démontré le concept de nano-antenne plasmonique hélicoïdale à ondes progressives (TW-HPA), c’est-à-dire un fil hélicoïdal en or étroit alimenté optiquement par une nano-antenne dipolaire dans une configuration « end-firing ». Une telle nano-antenne a été démontrée comme la première optique de polarisation sublongueur d’onde. L’agencement de TW-HPAs à l’échelle de quelques microns a permis de convertir « à la carte » un faisceau polarisé linéairement en une distribution de faisceaux directifs présentant des polarisations différentes définies de façon déterministe par la géométrie et les dimensions des nano-antennes. Par le biais d’un couplage en champ proche de quatre nano-antennes à hélicités opposées, nous avons obtenus une optique sublongueur d’onde permettant un degré de liberté dans le contrôle de la polarisation qui est interdit avec les composants et méthodes classiques basées sur l’exploitation de matériaux biréfringents ou dichroïques, ou de métamatériaux imitant ces propriétés. / My thesis is devoted to novel nano-optical phenomena and devices based on spin-orbit interaction (SOI) of light. First, magnetic spin-locking, i.e., an SOI solely driven by the magnetic field of light, is demonstrated with Bloch surface waves. It provides a new manifestation of the magnetic light field. Then, we propose and demonstrate the concept of traveling-wave plasmonic helical antenna (TW-HPA), consisting of a narrow helical gold-coated wire non-radiatively fed with a dipolar nano-antenna. By swirling surface plasmons, the TW-HPA combines subwavelength illumination and polarization transformation. The TW-HPA is demonstrated to radiate on the subwavelength scale almost perfectly circularly polarized optical waves upon illumination with linearly polarized light. With this subwavelength plasmonic antenna, we developed strongly integrated arrays of point-light emissions of opposite handedness and tunable intensities. Finally, by coupling two couples of TW-HPAs of opposite handedness, we obtained new polarization properties so far unattainable.

No description available.

The effect of spin-orbit coupling had once been thought to be a minor perturbation to the low energy band structure that could be ignored. Instead, a surge in recent theoretical and experimental efforts have shown spin-orbit interactions to have significant consequences. The main objective of this thesis is to investigate the role of the orbital sector and crystal symmetries in governing the spin texture in materials that have strong spin- orbit interactions. This can be accessed through a combination of spin- and angle-resolved photoemission spectroscopy (ARPES and spin-ARPES), both of which are powerful techniques for probing the one-electron band structure plus interactions, and supported by density functional theory calculations (DFT). We focus first on a globally inversion asymmetric material, the layered semiconductor BiTeI, which hosts a giant spin-splitting of its bulk bands. We show that these spin-split bands develop a previously undiscovered, momentum-space ordering of the atomic orbitals. We demonstrate this orbital texture to be atomic element specific by exploiting resonant enhancements in ARPES. These orbital textures drive a hierarchy of spin textures that are then tied to the constituent atomic layers. This opens routes to controlling the spin-splitting through manipulation of the atomic orbitals. This is contrasted against a material where inversion symmetry is globally upheld but locally broken within each monolayer of a two layer unit cell. Through our ARPES and spin-ARPES measurements of 2H-NbSe2, we discover the first experimental evidence for a strong out-of-plane spin polarisation that persists up to the Fermi surface in this globally inversion sym- metric material. This is found to be intrinsically linked to the orbital character and dimensionality of the underlying bands. So far, previous theories underpinning this (and related) materials' collective phases assume a spin- degenerate Fermi sea. We therefore expect this spin-polarisation to play a role in determining the underlying mechanism for the charge density wave phase and superconductivity. Through these studies, this thesis then develops the importance of global versus local inversion symmetry breaking and uncovers how this is intricately tied to the underlying atomic orbital configuration.

La dynamique des parois de domaine magnétiques (DW) soulève actuellement un très fort intérêt à la fois du point de vue fondamental mais aussi en lien avec ses applications dans des dispositifs logique et mémoire. Des dispositifs nouveaux basés sur les DW ont déjà été proposés, par exemple présentant des très fortes densités de stockage et des taux de transfert élevés pour un remplacement des disques durs. De plus dans les Mémoires Magnétiques à Accès Aléatoire (MRAM), identifiées comme l'une des solutions les plus prometteuses pour le remplacement des DRAM et SRAM, le retournement de l'aimantation implique une propagation des DW. Le contrôle de la dynamique des DW sous courant est longtemps resté un challenge, principalement à cause d'imperfections dans les matériaux utilisés. Des déplacements rapides et contrôlé des DW au moyen d'un courant ont été reportés il y a quelques années seulement dans des multicouches présentant une asymétrie d'inversion (SIA). Plus récemment un mécanisme a été proposé basé sur la présence de couple de spin orbite (SOT) et de l'interaction Dzyaloshinskii-Moriya (DMI), tout deux trouvant leur origine dans l'interaction spin-orbite et nécessitant une SIA.Mon objectif initial était de tester ce modèle dans deux systèmes présentant différents SIA. Dans des multicouches Pt/Co/Pt à faible SIA, j'ai étudié la propagation des DW sous courant et sous champ et j'ai mis en évidence l'existence d'un amortissement chiral. Ce phénomène nouveau, pendant de DMI pour les mécanismes dissipatifs, influence à la fois la dynamique sous courant et sous champ et doit être pris en compte pour avoir une description complète des mécanismes. Dans des multicouches Pt/Co/AlOx à fort SIA, j'ai étudié de nouvelles géométries pour lesquelles le mouvement de la paroi de domaine et la direction du courant ne sont pas colinéaires. J'ai mis en évidence un déplacement asymétrique des DW en fonction de cette non-colinéarité qui ne peut pas être expliquée avec un modèle simple DMI+SOT. En se basant sur ces résultats expérimentaux, j'ai introduit un nouveau concept de dispositifs, appelé « origami magnétique » : la forme du dispositif gouverne le mécanisme de retournement. Ce concept apporte une grande flexibilité dans la construction de mémoires magnétiques non volatiles, rapides et peu gourmandes en énergie : des fonctionnalités différentes peuvent être obtenues sur un même wafer simplement par la maîtrise de la forme des différents éléments. Je montre la preuve de concept de deux dispositifs. / Magnetic domain wall (DW) dynamics is currently attracting tremendous interest both from a fundamental point of view as well as in relation with emerging magnetic memory and logic devices. New DW-based devices were recently proposed, for example to replace hard drive disks with higher density and faster date transfer. Moreover, in Magnetic Random Access Memory (MRAM), identified as one of the most promising candidate for DRAM and SRAM replacement, switching occurs through DW propagation. Control of current induced DW dynamics has long been a challenge mainly due to material imperfections. Only some years ago, fast and controllable motions were reported in multilayers presenting structural inversion asymmetry (SIA). More recently, a mechanism was proposed based on the presence of spin orbit torques and Dzyaloshinskii-Moriya interaction (DMI), both phenomena originating from the spin orbit interaction and needing (SIA).My initial objective was to test this model in two systems presenting different SIA. In Pt/Co/Pt multilayers with weak SIA, I studied both current and field induced DW motion and evidenced a chiral damping. This new phenomena, counterpart of the DMI for the dissipative aspects, influences both current and field induced dynamics and has to be taken into account for a complete picture of the mechanism. In Pt/Co/AlOx multilayers with strong SIA, I studied new geometries where the DW motion the and current flow are not collinear. I evidenced asymmetric DW motion as a function of this non-collinearity that cannot be explained with a simple SOT+DMI model. Based on these experimental results I introduce a new device concept named “magnetic origami”: the shape of the device governs the switching mechanism. This concept provides large flexibility to construct fast, low power non-volatile magnetic memory: different functionalities can be achieved on a wafer by simply mastering the shape of the different elements. I show the proof of concept of two such devices.