Letteratura scientifica selezionata sul tema "Light-Induced magnetism"

Le magnétisme induit par la lumière décrit l'effet par lequel un matériau est magnétisé par une impulsion optique. Dans les matériaux transparents, la magnétisation induite optiquement peut être réalisée directement par la lumière polarisée circulairement. Parfois, dans les matériaux métalliques, ce type de magnétisation existe également en raison du trajet solénoïdal microscopique des électrons entraînés par la lumière polarisée circulairement. Dans certains cas, la lumière crée des courants de dérive continus circulants macroscopiques, qui induisent également une magnétisation continue dans le métal. De manière générale, ces magnétismes induits par la lumière sont connus sous le nom d'effet Faraday inverse. Dans le projet de doctorat, j'ai étudié les courants de dérive induits par la lumière dans plusieurs nanoantennes en or. Nous avons réalisé des champs magnétiques stationnaires amplifiés plasmoniquement grâce à ces courants de dérive. L'étude est basée sur la méthode des différences finies dans le domaine temporel (FDTD) et les théories correspondantes du magnétisme induit par la lumière. Dans différents sujets de recherche, nous avons réalisé : 1) un champ magnétique stationnaire ultra-rapide, confiné et fort dans une nanoantenne en forme d'œil de taureau. 2) Un champ magnétique stationnaire à travers une polarisation linéaire dans un nanorod. 3) Un skyrmion de type Neel construit par un champ magnétique stationnaire dans un nanoring. Dans ces études, nous avons examiné les propriétés optiques de différentes nanoantennes et expliqué l'origine physique des courants de dérive induits par la lumière et des champs magnétiques stationnaires. Nous avons démontré la méthode pour obtenir des effets Faraday inverses amplifiés plasmoniquement et exploré la possibilité de réaliser une magnétisation par la lumière incidente polarisée linéairement. Enfin, nous avons étendu l'effet Faraday inverse à d'autres domaines de recherche physique, tels que la construction de skyrmions par des champs magnétiques stationnaires à travers l'effet Faraday inverse. L'effet magnétique de la lumière reste un domaine de recherche riche. Mes études pourraient trouver des applications dans de nombreux domaines, y compris les matériaux et dispositifs magnéto-optiques, le stockage de données optiques, les applications biomédicales, la spintronique, l'informatique quantique, la recherche fondamentale en électromagnétisme et la recherche sur les matériaux avancés<br>Light-induced magnetism describes the effect where a material is magnetized by an optical pulse. In transparent materials, optically-induced magnetization can be realized directly by circularly polarized light. Sometimes, in metallic materials, this type of magnetization also exists due to the microscopic solenoidal path of electrons driven by circularly polarized light. In some cases, the light creates macroscopic circulating DC drift currents, which also induce DC magnetization in metal. In a broad sense, these light-induced magnetisms are known as the inverse Faraday effect.In the PhD project, I studied light-induced drift currents in multiple gold nanoantennas. We realized plasmonically enhanced stationary magnetic fields through these drift currents. The study is based on the Finite-Difference Time-Domain (FDTD) method and the corresponding light-induced magnetism theories. In different research topics, we have realized: 1) an ultrafast, confined, and strong stationary magnetic field in a bull-eye nanoantenna. 2) A stationary magnetic field through linear polarization in a nanorod. 3) A Neel-type skyrmion constructed by a stationary magnetic field in a nanoring. In these studies, we examined the optical properties of different nanoantennas and explained the physical origin of light-induced drift currents and stationary magnetic fields. We demonstrated the method to achieve plasmonically enhanced inverse Faraday effects and explored the possibility of realizing magnetization through linearly polarized incident light. Finally, we extended the inverse Faraday effect to more physical research areas, such as constructing skyrmions by stationary magnetic fields through the inverse Faraday effect.The magnetic effect of light remains a rich area of research. My studies might find applications in many areas, including magneto-optical materials and devices, optical data storage, biomedical applications, spintronics, quantum computing, fundamental research in electromagnetism, and advanced materials research

L'effet LIESST (Light-Induced Excited Spin-State Trapping) apparaît comme l'un des phénomènes les plus prometteurs et les plus excitants pour les dispositifs applicatifs basés sur les complexes à transition de spin (TS). Cependant, la compréhension fondamentale du LIESST doit encore être approfondie avant toute conception rationnelle. Par exemple, il est encore très difficile d'établir les relations structure-propriétés, bien que cette approche soit cruciale pour découvrir des matériaux à TS ayant une température de relaxation T(LIESST) élevée. L'objectif de ce travail est donc de comprendre comment augmenter la valeur de T(LIESST) vers une plage de température de la vie quotidienne. Nous avons choisi de l’atteindre en tentant d’augmenter la distorsion de la sphère de coordination du métal par deux stratégies basées sur la chimie : i) influer à l'échelle moléculaire via des contraintes stériques induites par des ligands halogénés et ii) moduler la contrainte moléculaire via du polymorphisme. La partie I présente quelques aspects fondamentaux et les parties II et III sont consacrées à la synthèse, à la cristallographie et aux études (photo)magnétiques des nouveaux composés moléculaires, y compris des polymorphes, de la famille [Fe(PM-L)2(NCX)2]. Ces nouveaux composés offrent tout d'abord un large éventail de comportements innovants, comme par exemple des expansions volumiques négatives ou nulles à la TS et l'absence de transition à plusieurs étapes malgré des sites métalliques indépendants au sein du cristal. Ces travaux élargissent considérablement la richesse des perspectives du phénomène de TS. De plus, l'examen approfondi des paramètres pertinents pour l’obtention d’un T(LIESST) élevé, tel que discutés dans la partie IV, apporte de nouvelles caractéristiques et prouve définitivement que toutes les échelles physiques doivent être prises en compte, ce qui conduit à proposer un concept multi-échelle de l'effet LIESST<br>The Light-Induced Excited Spin-State Trapping effect (LIESST) appears as one of the most promising and exciting phenomena for applicative devices based on Spin-CrossOver (SCO) complexes. However, the fundamental understanding of the LIESST effect must be yet deeply completed prior to any rational design of any efficient material. For instance, it is still a great challenge to establish the structure-properties relationships corresponding to the LIESST process, though this approach is crucial to discover SCO materials with a high relaxation temperature T(LIESST). The target of this work is therefore to understand how to increase T(LIESST) towards a daily-life temperature range. We choose to reach this goal by increasing the distortion of the metal coordination sphere through two chemistry-based strategies: i) playing at the molecular scale via steric strains produced by halogen-substituted ligands and ii) controlling the molecular stress through polymorphism. Part I displays some fundamental knowledge on SCO and Part II and III are devoted to the synthesis, crystallography and (photo)magnetic studies of new molecular compounds, including polymorphs, of the [Fe(PM-L)2(NCX)2] family. First these new compounds offer a large panel of innovative behaviours, such as, for instance, negative or zero volume expansions at the SCO and the absence of multi-step transition despite independent metal sites within the crystal. This work enlarges significantly the richness of the SCO based perspectives. Second, the deep examination of the relevant parameters to high T(LIESST) as discussed in Part IV brings new features and, overall, definitively proves that all physical scales must be taken into account, leading to a multiscale concept of the LIESST effect

La simulation des Hamiltoniens de réseaux dans les plateformes photoniques a permis de mieux comprendre les nouvelles propriétés de transport et de localisation dans le contexte de la physique de l'état solide. En particulier, les exciton-polaritons constituent un système polyvalent permettant d'étudier ces propriétés dans des réseaux avec des structures de bande intrigantes en présence de pertes et de gains, et d'interactions entre particules. Les polaritons sont des quasi-particules hybrides lumière-matière résultant du couplage fort entre les photons et les excitons dans les microcavités semi-conductrices, dont les propriétés peuvent être directement accessibles dans les expériences de photoluminescence. Dans cette thèse, nous étudions premièrement les caractéristiques des réseaux en nid d'abeille déformés, composés de résonateurs de polaritons couplés, à haut contenu photonique. Dans un réseau déformé de façon critique, nous mettons en évidence à la fois un transport semi-Dirac et une localisation anisotrope des photons. Deuxièmement, nous montrons qu'un forçage judicieux dans des réseaux de résonateurs à pertes permet l'apparition de nouveaux modes localisés. En utilisant des réseaux de polaritons sous un forçage résonant par plusieurs faisceaux optiques, nous démontrons la possibilité de localiser la lumière sur différentes géométries, voir jusqu'à un seul site. Enfin, nous profitons de l'interaction de polaritons dépendant de la polarisation pour démontrer un effet optique de type Zeeman dans un seul micropilier. En combinant le couplage spin-orbite optique, inhérent aux microstructures semi-conductrices, avec l'effet Zeeman, induit par l'interaction, nous montrons l'émission de faisceaux de vortex avec une chiralité bien définie. Cette thèse met en lumière la puissance des plateformes de polaritons pour étudier les Hamiltoniens de réseaux avec des propriétés sans précédent. Elle apporte également un premier pas vers la génération, entièrement optique, de phases topologiques dans les réseaux<br>The simulation of lattice Hamiltonians in photonic platforms has been enlightening in the understanding of novel transport and localization properties in the context of solid-state physics. In particular, exciton-polaritons provide a versatile system to investigate these properties in lattices with intriguing band structures in the presence of gain and loss, and particle interactions. Polaritons are hybrid light-matter quasiparticles arising from the strong coupling between photons and excitons in semiconductor microcavities, whose properties can be directly accessed in photoluminescence experiments. In this thesis, we firstly study the features of strained honeycomb lattices made of coupled polariton resonators having high photonic content. In a critically strained lattice, we evidence both a semi-Dirac transport and an anisotropic localization of photons. Secondly, we show that a judicious driving in lattices of lossy resonators allows the appearance of novel localized modes. Using polariton lattices driven resonantly with several optical beams, we demonstrate the localization of light in at-will geometries down to a single site. Finally, we take advantage of the polarization-dependent polariton interaction to demonstrate an optical Zeeman-like effect in a single micropillar. In combination with optical spin-orbit coupling inherent to semiconductor microstructures, the interaction-induced Zeeman effect results in emission of vortex beams with a well-defined chirality. This thesis brings to light the power of polariton platforms to study lattice Hamiltonians with unprecedented properties and it also provides a first step towards the fully-optical generation of topological phases in lattices

In this thesis, we have studied the coherence effects in atoms induced by light and a magnetic field. After giving an introduction to the contents of the thesis, details about the theory and the experimental setup used are given. The next few chapters contain the experimental results backed by a theoretical understanding. Only the joint work with the Armenian group (paper titled “Study of EIT resonances in an anti-relaxation coated Rb vapor cell” published in Physics Letters A) is one where they did the experiment and we did the theory. The thesis ends with a discussion about the various results presented. In the first work, the magnetic field induced coherence effect is studied in the light of the Hanle effect. We have studied the transformation of a Hanle EIT to a Hanle EIA for a circularly polarized beam in presence of a spatially separated control beam whose ellipticity is varied. A density matrix model describing three regions of interaction is developed to reproduce the experimental results. The second work describes the use of CPT/EIT system in a double-lambda configuration to interfere beams in one lambda system while the other lambda system acts as a phase reference. This process of light interference mediated by atomic coherence is extended to propose a system in which interference between two beams 10s of GHz apart in frequency could be detected on a low bandwidth (10s of MHz) optical detector. The third work describes an observation of EIA in a vee + ladder system in 87Rb. The vee system is formed by using the D1 line of 87Rb as control and the D2 line as the probe, and the ladder system is formed by the same probe as in vee system and a beam on the transition from 5P3/2 to 5D5/2 as control. The fourth work, done along with our collaborators in Armenia, shows splitting of EIT into dark and bright resonance in the presence of a strong transverse magnetic field in an anti-relaxation coated cell in the D1 line of 87Rb. We have performed a density matrix analysis using all the magnetic sublevels to reproduce the experimental results. The tunability of such a system between super-luminal and sub-luminal propagation for a probe beam is also theoretically discussed.

In this PhD thesis, we study the interplay between symmetry-breaking order and quantum-disordered phases in the milieu of frustrated quantum magnets, and further show how the excitation process of long-wavelength (semi-)classical modes in spin-orbit coupled antiferromagnets crucially depends on the nature and interactions of the underlying quantum quasiparticles. First, we focus on Kitaev's exactly solvable model for a Z2 spin liquid as a building block for constructing novel phases of matter, utilizing Majorana mean-field theory (MMFT) to map out phase diagrams and study occurring phases. In the Kitaev Kondo lattice, conduction electrons couple via a Kondo interaction to the local moments in the Kitaev model. We find at small Kondo couplings a fractionalized Fermi liquid (FL*) phase, a stable non-Fermi liquid where conventional electronic quasiparticles coexist with the deconfined excitations of the spin liquid. The transition between FL* and a conventional Fermi liquid is masked by an exotic (confining) superconducting phase which exhibits nematic triplet pairing, which we argue to be mediated by the Majorana fermions in the Kitaev spin liquid. We moreover study bilayer Kitaev models, where two Kitaev honeycomb spin liquids are coupled via an antiferromagnetic Heisenberg interaction. Varying interlayer coupling and Kitaev coupling anisotropy, we find both direct transitions from the spin liquid to a trivial dimer paramagnet as well as intermediate 'macrospin' phases, which can be studied by mappings to effective transverse-field Ising models. Further, we find a novel interlayer coherent pi-flux phase. Second, we consider the stuffed honeycomb Heisenberg antiferromagnet, where recent numerical studies suggest the coexistence of collinear Néel order and a correlated paramagnet, dubbed 'partial quantum disorder'. We elucidate the mechanism which drives the disorder in this model by perturbatively integrating out magnons to derive an effective model for the disordered sublattice. This effective model is close to a transition between two competing ground states, and we conjecture that strong fluctuations associated with this transition lead to disorder. Third, we study the generation of coherent low-energy magnons using ultrafast laser pulses in the spin-orbit coupled antiferromagnet Sr2IrO4, inspired by recent pump-probe experiments. While the relaxation dynamics of the system at long time scales can be well described semi-classically, the ultrafast excitation process is inherently non-classical. Using symmetry analysis to write down the most general coupling between electric field and spin operators, we subsequently integrate out high-energy spin fluctuations to derive induced effective fields which act to excite the low-energy magnon, constituting a generalized 'inverse Faraday effect'. Our theory reveals a tight relationship between induced fields and the two-magnon density of states.:1 Introduction 1.1 Frustrated antiferromagnets 1.2 Quantum spin liquids 1.3 Fractionalization and topological order 1.4 Spin-orbit coupling 1.5 Outline I Novel phases by building on Kitaev’s honeycomb model 2 Kitaev honeycomb spin liquid 2.1 Microscopic spin model and constants of motion 2.2 Majorana representation of spin algebra 2.3 Exact solution 2.3.1 Ground state 2.3.2 Correlations and dynamics 2.3.3 Thermodynamic properties 2.4 Z2 gauge structure 2.5 Toric code 2.6 Topological order 2.6.1 Superselection sectors and ground-state degeneracy 2.6.2 Topological entanglement entropy 2.6.3 Symmetry-enriched and symmetry-protected topological phases 3 Mean-field theory 3.1 Generalized spin representations 3.1.1 Parton constructions 3.1.2 SO(4) Majorana representation 3.2 Projective symmetry groups 3.3 Mean-field solution of the Kitaevmodel 3.4 Comparisonwithexactsolution 3.4.1 Spectral properties 3.4.2 Correlation functions 3.4.3 Thermodynamic properties 3.5 Generalized decoupling 3.6 Comparison to previous Abrikosov fermion mean-field theories of the Kitaev model 3.7 Discussion 4 Fractionalized Fermi liquids and exotic superconductivity in the Kitaev Kondo lattice 4.1 Metals with frustration 4.2 Local-moment formation and Kondo effect 4.2.1 Single Kondo impurity 4.2.2 Kondo lattices and heavy Fermi liquids 4.3 Fractionalized Fermi liquids 4.4 Construction of the Kitaev Kondo lattice 4.4.1 Hamiltonian 4.4.2 Symmetries 4.5 Mean-field decoupling of Kondo interaction 4.5.1 Solution of self-consistency conditions 4.6 Overview of mean-field phases 4.7 Fractionalized Fermi liquid 4.7.1 Results from mean-field theory 4.7.2 Perturbation theory beyond mean-field theory 4.8 Heavy Fermi liquid 4.9 Superconducting phases 4.9.1 Spontaneously broken U(1) phase rotation symmetry 4.9.2 Excitation spectrum and nematicity 4.9.3 Topological triviality 4.9.4 Group-theoretical classification 4.9.5 Pairing glue 4.10 Comparison with a subsequent study 4.11 Discussion and outlook 5 Bilayer Kitaev models 5.1 Model and stacking geometries 5.1.1 Hamiltonian 5.1.2 Symmetries and conserved quantities 5.2 Previous results 5.3 Mean-field decoupling and phase diagrams 5.3.1 AA stacking 5.3.2 AB stacking 5.3.3 σAC stacking 5.3.4 σ ̄AC stacking 5.4 Quantum phase transition in the AA stacking 5.4.1 Perturbative analysis 5.5 Phase transition in the σAC stacking 5.6 Macro-spin phases 5.6.1 KSL-MAC transition: Effective model for Kitaev dimers 5.6.2 DIM-MAC transition: Effective theory for triplon condensation 5.6.3 Macro-spin interactions and series expansion results 5.6.4 Antiferromagnet in the AB stacking 5.7 Stability of KSL and the interlayer-coherent π-flux phase 5.7.1 Perturbative stability of the Kitaev spin liquid 5.7.2 Spontaneous interlayer coherence near the isotropic point 5.8 Summary and discussion II Partial quantum disorder in the stuffed honeycomb lattice 6 Partial quantum disorder in the stuffed honeycomb lattice 6.1 Definition of the stuffed honeycomb Heisenberg antiferromagnet 6.2 Previous numerical results 6.3 Derivation of an effective model 6.3.1 Spin-wave theory for the honeycomb magnons 6.3.2 Magnon-central spin vertices 6.3.3 Perturbation theory 6.3.4 Instantaneous approximation 6.3.5 Truncation of couplings 6.3.6 Single-ion anisotropy 6.3.7 Discussion of most dominant interactions 6.4 Analysis of effective model 6.4.1 Classical ground states 6.4.2 Stability of classical ground states in linear spin-wave theory 6.4.3 Minimal model for incommensurate phase 6.4.4 Discussion of frustration mechanism in the effective model 6.5 Partial quantum disorder beyond the effectivemodel 6.5.1 Competition between PD and the (semi-)classical canted state 6.5.2 Topological aspects 6.5.3 Experimental signatures 6.6 Discussion 6.6.1 Directions for further numerical studies 6.6.2 Experimental prospects III Optical excitation of coherent magnons 7 Ultrafast optical excitation of magnons in Sr2IrO4 7.1 Pump-probe experiments 7.2 Previous approaches to the inverse Faraday effect and theory goals 7.3 Sr2IrO4 as a spin-orbit driven Mott insulator 7.4 Spin model for basal planes in Sr2IrO4 7.4.1 Symmetry analysis 7.4.2 Classical ground state and linear spin-wave theory 7.4.3 Mechanism for in-plane anisotropy 7.5 Pump-induced dynamics 7.5.1 Coupling to the electric field: Symmetry analysis 7.5.2 Keldysh path integral 7.5.3 Low-energy dynamics 7.5.4 Driven low-energy dynamics 7.6 Derivation of the induced fields 7.6.1 Perturbation theory 7.6.2 Evaluation of loop diagram 7.6.3 Analytical momentum integration in the continuum limit 7.6.4 Numerical evaluation of effective fields 7.7 Analysis of induced fields 7.7.1 Polarization and angular dependence 7.7.2 Two-magnon spectral features 7.8 Applications to experiment 7.8.1 Predictions for experiment 7.8.2 Magnetoelectrical couplings 7.9 Discussion and outlook 8 Conclusion and outlook 8.1 Summary 8.2 Outlook IV Appendices A Path integral methods B Spin-wave theory B.1 Holstein-Primakoff bosons B.2 Linear spin-wave theory B.2.1 Diagonalization via Bogoliubov transformation B.2.2 Applicability of linear approximation B.3 Magnon-magnon interactions B.3.1 Dyson's equation and 1/S consistency B.3.2 Self-energy from quartic interactions in collinear states on bipartite lattices C Details on the SO(4) Majorana mean-field theory C.1 SO(4) Matrix representation of SU(2) subalgebras C.2 Generalized SO(4) Majorana mean-field theory for a Heisenberg dimer (Chapter 3) C.3 Dimerization of SO(4) Majorana mean-field for the Kitaev model (Chapter3) C.4 Mean-field Hamiltonian in the Kitaev Kondo lattice (Chapter 4) C.5 Example solutions in the superconducting phase for symmetry analysis (Chapter4) D Linear spin-wave theory for macrospin phase in the bilayer Kitaev model (Chapter 5) D.1 Spin-wave Hamiltonian and Bogoliubov rotation D.2 Results and discussion E Extrapolation of the effective couplings for the staggered field h -> 0 (Chapter 6) E.1 xy interaction E.1.1 Leadingorder ~ S0 E.1.2 Subleadingorder ~ S^(−1) E.2 z-Ising interaction F Light-induced fields by analytical integration (Chapter 7) F.1 Method F.2 Results Bibliography

Wydział Fizyki.<br>The goal of the thesis is to addree the interaction of light with Co/garnet heterostructures, in order to achieve an understanding in this area that we call "femtomagnetism". In Chapter I, an introduction to ultrafast dynamics is presended. Chapter II gives short overview of magnetic properties with the focus on photomagnetism in garnets. Chapter III provides the basic introduction into the experimental techniques. In Chapter IV, we demostrate how damage-free etching of garrnet films allows us to form the Co/garnet heterostructures. In Chapter V the magnetic and magneto-optical properties of Co/garnet heterostructures were presented. Chapter VI deals studies of surface/interfaces in heterostructures in a wide spectral range. In Chapter VII, we demonstrate the results laser-induced magnetization dynamics, photoinduced magnetic anisotropy in bare garnet films and modulation of spin precession in Co/garnet heterostructures. Furthermore, it is shown that the magnetisation precession in the garnet film can be manipulated by the strong magnetostatic coupling between Co and garnet layers. These findings could provide new possibilities in optical excitation and local spin manipulation by polarized femtosecond pulses for the application in the new magnetic storage memory with high speed recording.<br>Głównym celem niniejszej rozprawy są badania oddziaływania światła laserowego z heterostrukturą Co/granat, jak również głębsze zrozumienie zjawisk fizyki magnetyzmu w skali femtosekundowej - tzw. "femtomagnetyzmu". Rozdział I obejmuje wprowadzenie do ultraszybkiej dynamiki magnetyzacji. W Rozdziale II umieszczono krótki przegląd właściwości magnetycznych oraz zjawiska fotomagnetyzmu w cienkich warstwach granatów itrowo-żelazowych. W Rozdziale III opisano główne techniki eksperymentalne. W Rozdziale IV przedstawiono metodę wytworzenia magnetycznych heterostruktur kobalt/granat o różnych grubościach. Rozdział V zawiera opis podstawowych właściwości magnetooptycznych i magnetycznych heterostruktur. W Rozdziale VI przedstawiono wyniki badań spektralnych powierzchni/interfejsów heterostruktur. Rozdział VII prezentuje wyniki badań ultraszybkiej dynamiki magnetyzacji, fotoindukowanej anizotropii w warstwach granatu oraz efekt modulacji precesji spinów w heterostrukturze Co/granat. Także zaobserwowano zmianę fazy precesji magnetyzacji w warstwie granatu w zakresie sprzężenia magnetostatycznego z warstwą kobaltu. Zawarte w rozprawie wyniki, prezentujące szerokie możliwości wzbudzeń optycznych oraz lokalną manipulację spinem przy wykorzystaniu spolaryzowanego światła laserowego, rokują nadzieje na zastosowania w nowych pamięciach magnetycznych o dużej szybkości zapisu.<br>The work described in this thesis was financially supported by the EU 7 Framework Programme (FP7/2007- 2013) under grant agreement No. 214810 (FANTOMAS), the SYMPHONY project operated within the Foundation for Polish Science Team Program co-financed by the EU European Regional Development Fund, OPIE 2007-2013 and the National Science Centre Poland for OPUS project DEC-2013/09/B/ST3/02669.