Добірка наукової літератури з теми "Spin-orbit Coupling (SOC)"

Electrophilicity index (𝜔) is related to the energy lowering associated with a maximum amount of electron flow between a donor and an acceptor and possesses adequate information regarding structure, stability, reactivity and interactions. Chemical potential (μ) measures charge transfer from a system to another having a lower value of μ, while chemical hardness (η) is a measure of characterizing relative stability of clusters. The main purpose of the present research work is to examine the Spin-Orbit Coupling (SOC) effect on the behavior of the electrophilicity index, chemical potential, hardness and softness of neutral gold clusters Aun (n=2-6). Using the second-order Douglas-Kroll-Hess Hamiltonian, geometries are optimized at the DKH2-B3P86/DZP-DKH level of theory. Spin-orbit coupling energies are computed using the fourth-order Douglas-Kroll-Hess Hamiltonian, generalized Hartree-Fock method and all-electron relativistic double-ζ level basis set. Then, spin-orbit coupling (SOC) corrections to the electrophilicity index, chemical potential, hardness and softness are calculated. It is revealed that spin-orbit correction to the vertical chemical hardness has important effect on Au3 and Au6, i.e. SOC decreases (increases) the hardness of gold trimer (hexamer). Due to the relationship between hardness and softness, σ = , inclusion of spin-orbit coupling increases (decreases) the softness of Au3 (Au6) and thus destabilizes (stabilizes) it. Spin-orbit coupling (SOC) also has more important effect on the chemical potential of Au3 by decreasing its value. It is found that spin-orbit coupling has considerable effect on the electrophilicity index of gold trimer and greatly increases its value. Furthermore, SOC increases the maximal charge acceptance of Au3 more and thus destabilizes it more. As a result, spin-orbit coupling effect appears to be important in calculating the electrophilicity index of the gold trimer. Doi: 10.28991/HIJ-2021-02-01-05 Full Text: PDF

Interplay of spin-orbit coupling (SOC) and electron correlation generates a bunch of emergent quantum phases and transitions, especially topological insulators and topological transitions. We find that electron correlation will induce extra large SOC in multi-orbital systems under atomic SOC and change ground state topological properties. Using the Hartree–Fock mean field theory, phase diagrams of px /py orbital ionic Hubbard model on honeycomb lattice are well studied. In general, correction of strength of SOC δ λ ∝ (Uʹ–J). Due to breaking down of rotation symmetry, form of SOC on multi-orbital materials is also changed under correlation. If a non-interacting system is close to fermionic instability, spontaneous generalized SOC can also be found. Using renormalization group, SOC is leading instability close to quadratic band-crossing point. Mean fields at quadratic band-crossing point are also studied.

Abstract The electrical control of a spin qubit in a quantum dot (QD) relies on spin–orbit coupling (SOC), which could be either intrinsic to the underlying crystal lattice or heterostructure, or extrinsic via, for example, a micro-magnet. In experiments, micromagnets have been used as a synthetic SOC to enable strong coupling of a spin qubit in quantum dots with electric fields. Here we study theoretically the spin relaxation, pure dephasing, spin manipulation, and spin–photon coupling of an electron in a QD due to the synthetic SOC induced spin–orbit mixing. We find qualitative difference in the spin dynamics in the presence of a synthetic SOC compared with the case of the intrinsic SOC. Specifically, spin relaxation due to the synthetic SOC and deformation potential phonon emission (or Johnson noise) shows B 0 5 (or B 0) dependence with the magnetic field, which is in contrast with the B 0 7 (or B 0 3 ) dependence in the case of the intrinsic SOC. Moreover, charge noise induces fast spin dephasing to the first order of the synthetic SOC, which is in sharp contrast with the negligible spin pure dephasing in the case of the intrinsic SOC. These qualitative differences are attributed to the broken time-reversal symmetry (T-symmetry) of the synthetic SOC. An SOC with broken T-symmetry (such as the synthetic SOC from a micro-magnet) eliminates the ‘Van Vleck cancellation’ and causes a finite longitudinal spin–electric coupling that allows the longitudinal coupling between spin and electric field, and in turn allows spin pure dephasing. Finally, through proper choice of magnetic field orientation, the electric-dipole spin resonance via the synthetic SOC can be improved with potential applications in spin-based quantum computing.

Abstract The near-exact iCIPT2 approach for strongly correlated systems of electrons, which stems from the combination of iterative configuration interaction (iCI, an exact solver of full CI) with configuration selection for static correlation and second-order perturbation theory (PT2) for dynamic correlation, is extended to the relativistic domain. In the spirit of spin separation, relativistic effects are treated in two steps: scalar relativity is treated by the infinite-order, spin-free part of the exact two-component (X2C) relativistic Hamiltonian, whereas spin–orbit coupling (SOC) is treated by the first-order, Douglas–Kroll–Hess-like SOC operator derived from the same X2C Hamiltonian. Two possible combinations of iCIPT2 with SOC are considered, i.e., SOiCI and iCISO. The former treats SOC and electron correlation on an equal footing, whereas the latter treats SOC in the spirit of state interaction, by constructing and diagonalizing an effective spin–orbit Hamiltonian matrix in a small number of correlated scalar states. Both double group and time reversal symmetries are incorporated to simplify the computation. Pilot applications reveal that SOiCI is very accurate for the spin–orbit splitting (SOS) of heavy atoms, whereas the computationally very cheap iCISO can safely be applied to the SOS of light atoms and even of systems containing heavy atoms when SOC is largely quenched by ligand fields.

Abstract We study the electronic structure and correlated phases of twisted bilayers of platinum diselenide using large-scale ab initio simulations combined with the functional renormalization group. PtSe2 is a group-X transition metal dichalcogenide, which hosts emergent flat bands at small twist angles in the twisted bilayer. Remarkably, we find that Moiré engineering can be used to tune the strength of Rashba spin–orbit interactions, altering the electronic behavior in a novel manner. We reveal that an effective triangular lattice with a twist-controlled ratio between kinetic and spin–orbit coupling (SOC) scales can be realized. Even dominant SOC can be accessed in this way and we discuss consequences for the interaction driven phase diagram, which features pronounced exotic superconducting and entangled spin-charge density waves.

Spin chemistry involving small organic molecules without heavy atoms is highly sensitive to spin-orbit-coupling (SOC) modulating biradical conformation as well as hyperfine coupling (HFC) modulating magnetic isotope interactions. Several easily available reaction properties such as chemo-, regio-, and diastereoselectivity as well as quantum yields serve as analytical tools to follow intersystem crossing dynamics and allows titrating spin selectivities.

Spin-orbit coupling (SOC), the interaction between the electron spin and the orbital angular momentum, can unlock rich phenomena at interfaces, in particular interconverting spin and charge currents. Conventional heavy metals have been extensively explored due to their strong SOC of conduction electrons. However, spin-orbit effects in classes of materials such as epitaxial 5d-electron transition-metal complex oxides, which also host strong SOC, remain largely unreported. In addition to strong SOC, these complex oxides can also provide the additional tuning knob of epitaxy to control the electronic structure and the engineering of spin-to-charge conversion by crystalline symmetry. Here, we demonstrate room-temperature generation of spin-orbit torque on a ferromagnet with extremely high efficiency via the spin-Hall effect in epitaxial metastable perovskite SrIrO3. We first predict a large intrinsic spin-Hall conductivity in orthorhombic bulk SrIrO3 arising from the Berry curvature in the electronic band structure. By manipulating the intricate interplay between SOC and crystalline symmetry, we control the spin-Hall torque ratio by engineering the tilt of the corner-sharing oxygen octahedra in perovskite SrIrO3 through epitaxial strain. This allows the presence of an anisotropic spin-Hall effect due to a characteristic structural anisotropy in SrIrO3 with orthorhombic symmetry. Our experimental findings demonstrate the heteroepitaxial symmetry design approach to engineer spin-orbit effects. We therefore anticipate that these epitaxial 5d transition-metal oxide thin films can be an ideal building block for low-power spintronics.

We investigate theoretically the spin accumulation of a quantum wire nonadiabatically connected to two normal leads in the presence of Rashba and Dresselhaus spin–orbit coupling (SOC). Using scattering matrix approach within the effective free-electron approximation, three components of spin polarization have been calculated. It is demonstrated that for the Dresselhaus SOC case the out-of-plane spin polarization does not form spin accumulation, and when the two SOC terms coexist the influence of Rashba SOC to the out-of-plane spin accumulation is dominant and symmetry of the spin accumulation is broken due to the existence of Dresselhaus SOC. Moreover, the formation of the out-of-plane spin accumulation is influenced by the ratio of Rashba and Dresselhaus strength, and when the ratio is very small the out-of-plane spin polarization does not show spin accumulation patterns. It is also shown that the spin accumulation for the system is an intrinsic one which can be distinguished from the extrinsic spin accumulation by changing the Rashba strength.

The spin–orbit splitting (E[Formula: see text]) of valence band maximum at the [Formula: see text] point is significantly smaller in 2D planner honeycomb structures of graphene, silicene, germanene and BN than that in the corresponding 3D bulk counterparts. For 2D planner honeycomb structure of SiC, it is almost same as that for 3D bulk cubic SiC. The bandgap which opens at the K and K[Formula: see text] points due to spin–orbit coupling (SOC) is very small in flat honeycomb structures of graphene and silicene, while in germanene it is about 2 meV. The buckling in these structures of graphene, silicene and germanene increases the bandgap opened at the K and K[Formula: see text] points due to SOC quadratically, while the E[Formula: see text] of valence band maximum at the [Formula: see text] point decreases quadratically with an increase in the magnitude of buckling.

Paper discusses the expected uncertainty of orbital parameters of binary stars as measured by the space-based gravitational wave observatory LISA (Laser Interferometer Space Antenna) and how the inclusion of spin in the model of the binary stars affects the uncertainty. The uncertainties are found by calculating the received gravitational wave from a binary pair and then performing a linear least-squares parameter estimation. The case of a 1500 solar mass black hole that is 20 years from coalescing with a 1000 solar mass black hole--both of which are 50 x 10^6 light years away--is analyzed, and the results show that the inclusion of spin has a negligible effect upon the angular resolution of LISA but can increase the accuracy in mass and distance measurements by factors of 15 and 65, respectively.

La molécule SO2 est connue depuis longtemps dans la pour son spectre d'absorption compliqué résultant de forts couplages entre les états électroniques impliqués. Cette longue histoire a récemment été complétée par de nouvelles études spectroscopiques résolues en temps; la spectroscopie de photoémission (TRPES) et la génération d'harmoniques d'ordre élevé. De nouvelles questions ont ainsi émergées, concernant le rôle des différents états électroniques excités, les différents couplages et leur temps caractéristiques. Pour répondre à ces questions, nous avons considéré, dans un premier temps, l'état électronique fondamental et les deux premiers états singulets excités. Ceux-ci interagissent par l'intermédiaire de couplage non-adiabatic, conduisant à la complexité du spectre d'absorption. Nos résultats se sont avérés particulièrement précis, en particulier pour la description des bandes de Cléments, donnant lieu à leur première description et interprétation théorique. Le couplage spin-orbite et les états triplets ont été introduits dans la description du système et l'analyse de la dynamique a permis de comprendre les différents mécanismes de conversion intersystème. Trois résultats majeurs sont obtenus, (i) le rôle prédominant d'un état 3B2, (ii) la présence d'interférences quantiques lors du processus et (iii) une nouvelle interprétation de la bande dite " interdite ", émanant des état triplets. Les spectroscopies TRPES et HHG ont été utilisées pour sonder la dynamique moléculaire dans ces états. Grâce à des simulations ab-initio nous montrons que la méthode TRPES permet l'étude la dynamique pour tous les états alors que la HHG n'est sensible qu'à la conversion intersystème
The SO2 molecule is long known in the literature for its complex UV absorption spectrum, which is caused by a variety of strong couplings between the electronic states involved. This long and rich history was augmented recently by new time-dependent spectroscopic methods, namely, Time-Resolved Photoelectron Spectroscopy (TRPES) and High-order Harmonic Generation (HHG). Additional open questions emerged immediately, e.g., what was the role of the different known electronic states, which were the relevant couplings and also the timescales of the different relevant processes.To resolve these issues theoretically, we start by considering the electronic ground state and the two lowest singlet excited states. The latter interact through non-adiabatic couplings leading to a complex photoabsorption spectrum. Our results were accurate, especially concerning the Clements bands, and provide a comprehensive description of the photoabsorption spectrum. When including the spin-orbit coupling, relevant for the weak long-wavelength absorption system, the three-states model turns into a 12 coupled-states system. Analysis of the different couplings gives insight into the different mechanisms of the intersystem crossing. Three main points are shown: (i) the preponderant role of a 3B2 state, (ii) the possibility of quantum interferences during the process and (iii) a new interpretation of the forbidden band.The TRPES and the HHG spectroscopies have been used to probe the time-dependent dynamics in all these states. With the aid of first-principles simulations we show that the TRPES method is sensitive to the dynamics in the manifold, while HHG is sensitive only to the intersystem crossing

Orientadores: Narcizo Marques de Souza Neto, Flávio Cesar Guimarães Gandra
Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin
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Resumo: Este trabalho teve como objetivo a investigação de diversos mecanismos físicos provenientes das estruturas eletrônicas, magnéticas e cristalinas de sistemas ternários de terras raras e metais de transição 3d-5d através do uso das técnicas de espectroscopia de absorção de raios X e difração de raios X sob altas pressões. Dentre os fenômenos físicos estudados em função da compressão da rede cristalina induzida pela aplicação da pressão estão o magnetismo proveniente dos orbitais 4f e 5d nos sistemas ternários RERh4B4 (com RE = Dy e Er), os efeitos do campo elétrico cristalino e as interações de troca magnéticas nas perovskitas duplas 3d-5d (AFeOsO6, com A = Ca e Sr) e o acoplamento spin-órbita nos metais de transição 5d. As propriedades eletrônicas e magnéticas dos orbitais 4f e 5d das terras raras nos compostos da família RERh4B4 (RE = Dy e Er) foram investigadas através de experimentos de XANES e XMCD sob altas pressões na borda L3 do Dy e Er . Os sinais magnéticos das contribuições quadrupolar (2p3/2-> 4f) e dipolar (2p3/2->5d) presentes nos espectros de XMCD, em ambos os compostos, diminuem progressivamente em função da pressão. Este comportamento foi explicado em termos das interações de troca magnéticas entre os íons de terras raras, que são enfraquecidas pelas alterações locais da estrutura atômica induzidas pela compressão da rede cristalina. Já no sistema de perovskitas duplas, foi demonstrado que a compressão da estrutura Sr2FeOsO6, com um arranjo cristalino ordenado dos íons de Fe (3d) e Os (5d), permite o controle contínuo e reversível da coercividade e magnetização de saturação. Este efeito foi explicado em termos do aumento do campo elétrico cristalino em função da pressão, que altera as interações de troca magnéticas Fe-O-Os e transforma o material com magnetização remanente e coercividade praticamente nulas a pressão ambiente em outro com uma coercividade robusta (~0.5 T) e magnetização de saturação expressiva a pressões acima de ~10 GPa. Por fim, a última parte desta tese de doutorado foi dedicada ao uso da seletividade química e orbital da técnica de XANES na investigação do acoplamento spin-órbita nos elementos Pt (Pt0, 5d9) e Hf (Hf0, 5d2) sob altas pressões. Ao contrário do observado para a Pt, o cálculo do branching ratio a partir dos espectros de absorção nas bordas L2,3 do Hf revelaram que o acoplamento spin-órbita aumenta monotonicamente em função da pressão aplicada. Esse comportamento foi relacionado às propriedades supercondutoras e estruturais presentes nesse elemento sob altas pressões
Abstract: The scientific goal of this work has been the investigation of several physical mechanisms derived from the electronic, magnetic and structural properties of ternary rare earth and transition metal systems by means of X-ray absorption spectroscopy and X-ray diffraction techniques in a diamond anvil cell. Among the physical properties studied as a function of lattice compression induced by applied pressure are the magnetism of the 4f and 5d orbitals in tetragonal rare earth rhodium borides RERh4B4 (with RE = Dy e Er), the crystal electric field effects and magnetic exchange interactions in 3d-5d double perovskite systems (A2FeOsO6, with A = Ca e Sr) and the spin-orbit coupling in 5d transition metals. The electronic and magnetic properties of the rare earth 4f and 5d orbitals in the RERh4B4 (RE = Dy e Er) systems were investigated through high pressure XANES and XMCD experiments at Dy and Er L3 edges. For both compounds, the magnetic signals of the quadrupole (2p3/2->4f) and dipole (2p3/2->5d) contributions to the XMCD spectra progressively decrease as a function of pressure. This behavior was explained in terms of the magnetic exchange interactions between the rare earth ions, which are weakened by changes in the local atomic structure induced by compression of the crystal lattice. In the double perovskite system, it has been shown that compression of Sr2FeOsO6 structure with an ordered crystalline arrangement of iron (3d) and osmium (5d) transition metal ions, allows for continuous and reversible control of magnetic coercivity and saturation magnetization. This effect was explained in terms of enhanced crystal electric fields under high pressure, which alter the Fe-O-Os magnetic exchange interactions and transform the material with an otherwise mute response to magnetic fields into one with a strong coercivity (~0.5 T) and substantial saturation magnetization at pressures above ~10 GPa. Finally, the last part of this thesis is dedicated to the use of chemical and orbital selectivity of XANES technique as a tool to investigate the spin-orbit coupling in Pt (Pt0, 5d9) and Hf (Hf0, 5d2) elements under high pressures. Unlike observed for Pt, the calculated branching ratio determined from the integrated intensities of the Hf L2,3 white lines shows that the spin-orbit coupling increases monotonically as a function of applied pressure. This behavior was related to the superconducting and structural properties displayed by this element at high pressures
Doutorado
Física
Doutora em Ciências

This chapter delves into the physics of multiferroics, the recent developments of which are discussed here from the viewpoint of the spin current and “emergent electromagnetism” for constrained systems. It presents the three sources of U(1) gauge fields, namely, the Berry phase associated with the noncollinear spin structure, the spin-orbit interaction (SOI), and the usual electromagnetic field. The chapter reviews multiferroic phenomena in noncollinear magnets from this viewpoint and discusses theories of multiferroic behavior of cycloidal helimagnets in terms of the spin current or vector spin chirality. Relativistic SOI leads to a coupling between the spin current and the electric polarization, and hence the ferroelectric and dielectric responses are a new and important probe for the spin states and their dynamical properties. Microscopic theories of the ground state polarization for various electronic configurations, collective modes including the electromagnon, and some predictions including photoinduced chirality switching are discussed with comparison to experimental results.

A detailed analysis of electronic band structure of the ScAuSn, LuAuSn and their Superlattice have been performed using the full potential linearized augmented plane waves (FP-LAPW). The exchange-correlation between the electrons was treated with three schemes, generalized gradient approximation (GGA), Trans and Blaha modified Becke-Johnson potential (TB-mBJ) and Spin-Orbit Coupling (SOC) incorporated with GGA. The GGA method reveals an indirect spin-gapless semiconducting nature for LuAuSn, an indirect band gap semiconducting nature for ScAuSn and direct semiconducting nature for their superlattice whereas under mBJ scheme, the band gap values are found to be enhanced. The inclusion of Spin-Orbit Coupling effects in GGA predicts the materials to be semi-metallic. The density of states is mainly dominated by the Sc and Lu atom near the vicinity of Fermi energy level and in the conduction region in ScAuSn and LuAuSn alloys, respectively whereas in superlattice the density of states is mainly dominated by Sc atom with significant contribution from Sn atoms.

The implications of Einstein’s special relativity in chemistry are discussed. It is shown that relativistic effects on the electronic structure of an atom or molecule scales in leading order as Z2, where Z is the charge number of the heaviest nucleus in the system. Well-known heavy atom effects in chemistry are discussed: The color of gold, the liquid state of mercury, the inert pair effect of heavy p-block elements, and more. Spin-orbit coupling (SOC) is also a relativistic effect and plays a big role in spectroscopy and chemistry. The Dirac equation (DE) replaces the electronic Schrodinger equation in relativistic quantum chemistry. The Dirac wavefunctions have 4 components. It is shown how an ‘exact 2-component’ (X2C) Hamiltonian can be constructed. X2C based all-electron calculations are becoming increasingly popular in quantum chemical applications. Molecular properties may undergo a picture-change effect when going from a 4-component to a 2-component framework.

Quantum entanglement is a unique phenomenon of quantum mechanics that explains how two subatomic particles are correlated even if they are separated by a vast distance. The phenomena of quantum entanglement are useful resources for quantum information. In this chapter, we will study the entanglement properties of bipartite states of two electronic qubits, without observing spin-orbit interaction (SOI), produced by single-step double photoionization in helium atom following the absorption of a single photon. In absence of SOI, Russell-Saunders coupling (L-S coupling) is applicable. We observe that the entanglement depends significantly on the direction of the ejection, as well as the spin quantization of photoelectrons.