Spin-orbit Coupling Effects Research Articles

Rieger, Schwabe, Suess-de Vries: The Sunny Beats of Resonance

We propose a self-consistent explanation of Rieger-type periodicities, the Schwabe cycle, and the Suess-de Vries cycle of the solar dynamo in terms of resonances of various wave phenomena with gravitational forces exerted by the orbiting planets. Starting on the high-frequency side, we show that the two-planet spring tides of Venus, Earth, and Jupiter are able to excite magneto-Rossby waves, which can be linked with typical Rieger-type periods. We argue then that the 11.07-year beat period of those magneto-Rossby waves synchronizes an underlying conventional α−Ω\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$\\alpha-\\Omega $\\end{document}-dynamo by periodically changing either the field storage capacity in the tachocline or some portion of the α\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$\\alpha $\\end{document}-effect therein. We also strengthen the argument that the Suess-de Vries cycle appears as an 193-year beat period between the 22.14-year Hale cycle and a spin-orbit coupling effect related with the 19.86-year rosette-like motion of the Sun around the barycenter.

Wafer-scale synthesis of 2D PtTe2 thin films with high spin–orbit torque efficiency

Spintronic devices have become a crucial technology for overcoming the power consumption bottleneck in integrated circuits, due to their low power consumption, high-speed processing capability. Two-dimensional materials offer potential for performance enhancement and device miniaturization in spintronics because of their unique electronic and spin properties. Specifically, two-dimensional transition metal dichalcogenides (2D TMDs) are favored in the field of spintronics for their strong spin–orbit coupling effects, enabling effective control over the electron spin state. However, the preparation techniques for 2D TMDs are still in the exploratory stage. In this work, we explore novel preparation method combining magnetron sputtering and molecular beam epitaxy, leading to wafer-scale high-quality monocrystalline PtTe2 thin films. Further, Spin-Orbit Torque (SOT) efficiency is investigated in PtTe2-based heterostructures, which reveals a significant spin Hall angle of over 0.094. Our work provides a new way to fabricate the wafer-scale PtTe2 thin films and confirms a large SOT efficiency, which indicates the great promise for spintronic applications.

Quantum mechanical-like approach with non-Hermitian effective Hamiltonians in spin-orbit coupled optical cavities

We present a comprehensive analytical model of resonant states in birefringent microcavities with permeable mirrors. We derive an effective, non-Hermitian photonic Hamiltonian describing cavity mode dispersion and modal lifetimes by applying the Green's function technique based on the Mittag-Leffler expansion with respect to the resonant states and the k·p perturbation theory known from semiconductor physics. Using this formalism we obtained results which can be interpreted as effective cavity mode spin-orbit coupling. We use this method to derive the two-mode Hamiltonian to describe the properties of light in the cavity, which significantly reduces the computational effort and properly captures the polarization of the eigenmodes. This is done by introducing the necessary corrections to the Hamiltonian matrix and modifying the basis modes resulting from the coupling with other optical modes present in the system. This simplified Hamiltonian allows us to determine the positions of exceptional points in momentum space. These points are connected by Fermi arcs and appear due to non-Hermiticity and PT symmetry. Published by the American Physical Society 2024

Effect of lattice distortion on spin admixture and quantum transport in organic devices with spin–orbit coupling

Abstract With an extended Su–Schrieffer–Heeger model and Green’s function method, the spin–orbit coupling (SOC) effects on spin admixture of electronic states and quantum transport in organic devices are investigated. The role of lattice distortion induced by the strong electron–lattice interaction in organics is clarified in contrast with a uniform chain. The results demonstrate an enhanced SOC effect on the spin admixture of frontier eigenstates by the lattice distortion at a larger SOC, which is explained by the perturbation theory. The quantum transport under the SOC is calculated for both nonmagnetic and ferromagnetic electrodes. A more notable SOC effect on total transmission and current is observed for ferromagnetic electrodes, where spin filtering induced by spin-flipped transmission and suppression of magnetoresistance are obtained. Unlike the spin admixture, a stronger SOC effect on transmission exists for the uniform chain rather than the organic lattices with distortion. The reason is attributed to the modified spin-polarized conducting states in the electrodes by lattice configuration, and hence the spin-flip transmission, instead of the spin admixture of eigenstates. This work is helpful to understand the SOC effect in organic spin valves in the presence of lattice distortion.

Ground state structure and optoelectronic properties of novel quasi-2D layered halide perovskites CsPb2X5 (X= Cl, Br, I) via first principle calculations

The ground state structure and optoelectronic properties of novel quasi-2D layered halide perovskites CsPb2X5 (X= Cl, Br, I) are investigated for the possible optoelectronic applications in light emitting, photodetectors, photoemission, and photovoltaic (PV) devices using first principle-based calculations of the density functional theory (DFT). In the structure composition of CsPb2X5, 2Pb2+ atoms coordinated with eight X- anions build [Pb2X5]- polyhedral layers, where two layers of [Pb2X5]- polyhedron are separated by Cs+ (spacer cation) layers. The band gap nature of the studied semiconductors is indirect and spin orbit coupling (SOC) effect reduces the band gaps and splits the Pb-p and X-p orbitals at the edges of conduction and valence bands respectively. The wide and suitable band gaps of CsPb2X5 enable them for advanced technological applications in photodetectors, transistors, and optoelectronic devices. The dielectric functions, exciton binding energies, and carrier's effective masses show that CsPb2X5 are suitable materials for optoelectronic, photodetectors, and light emitting devices.

Theoretical electronic structure with spin–orbit coupling effect of the molecules SrAt and BaAt for laser cooling studies

Ab initio CASSCF/MRCI + Q calculations have been used to investigate the electronic structure and transition properties of the alkaline earth astatine molecules SrAt and BaAt. The adiabatic potential energy curves have been computed and plotted for the low-lying electronic states in the representations 2S+1Λ+/− and Ω(±) (with and without spin–orbit coupling effect). The spectroscopic and vibrational constants have been deduced for the corresponding bound states. An analysis of the Franck–Condon factors, the Einstein Coefficients, and the branching ratios among different vibrational levels has shown that both SrAt and BaAt molecules are suitable candidates for Doppler and Sysphus laser cooling. Experimental laser cooling schemes and conditions for these two molecules have been proposed. These results may pave the way for new spectroscopic and laser cooling experiments of alkaline earth astatine molecules.

Weak interatomic interactions induced low lattice thermal conductivity in 2D/2D PbSe/SnSe vdW heterostructure

Inspired by the excellent thermoelectric performance of two-dimensional (2D) PbSe and SnSe monolayers, the thermal and electronic transport properties of 2D/2D PbSe/SnSe heterostructure is theoretically evaluated using first-principles calculations and Boltzmann transport theory. An indirect bandgap of 1.06 eV for the PbSe/SnSe heterostructure is calculated by the combination of Heyd-Scuseria-Ernzerhof (HSE06) functional and spin-orbit coupling (SOC) effect. The mechanical, thermal and dynamic stabilities of the PbSe/SnSe heterostructure are further demonstrated by the elastic modulus, ab initio molecular dynamics (AIMD) simulations and phonon dispersion curves, respectively. The honeycomb-like wrinkled structure introduce the asymmetry at the interface of the PbSe/SnSe heterostructure, thereby leading to enhanced phonon boundary scattering. Concurrently, the antibonding states originated from the weak interatomic interactions within PbSe/SnSe heterostructure also lead to strong anharmonicity. This synergistic effect of pronounced scattering and heightened anharmonicity contributes to the low lattice thermal conductivity of PbSe/SnSe heterostructure. The thermoelectric properties of PbSe/SnSe heterostructure are further investigated along the x- and y-direction, which reveals that the p-type PbSe/SnSe heterostructure attains an optimal dimensionless figure-of-merit (ZT) of 2.6 at 900 K along the y-direction. Our present study not only offers the fundamental insights into the thermal and electronic transport properties of the PbSe/SnSe heterostructure, but also provides an effective and feasible strategy for the design of 2D layered heterostructures as promising thermoelectric materials.

First-principles calculations to investigate the elastic, electronic, dynamical, and optical properties of cubic ZrCoAs half-Heusler semiconductor for photovoltaic applications

The electronic, mechanical, elastic, dynamical, and optical properties of the ZrCoAs half-Heusler compound have been systematically investigated using the plane wave self-consistent field approach with the Perdew-Burke-Erzerhof generalized gradient approximation (GGA-PBE) exchange-correlation functional. The study includes examinations with and without spin orbit coupling (SOC) effects. Results indicate a decrease in the Kohn-Sham band gap with the inclusion of SOC effects. Electronic bandgap formation was attributed to Co 3d, Zr 3d, and As 2p for the conduction band, and Co 3d and As 2p for the valence band without SOC effects. With SOC, Co 5d, Zr 8d, and As 3p dominated the conduction band, while Co 3d and As 3p dominated the valence band. The lattice constant showed a 0. 063% decrease with the SOC effects, which is better aligned with the experimental observations. ZrCoAs demonstrated ductility, mechanical stability, and dynamical stability. The optical properties were found to be excellent for photovoltaic applications, suggesting its potential in solar energy conversion technology. This study provides valuable information on ZrCoAs and presents opportunities for its use in solar cells, optoelectronic devices, and thermoelectric applications. The material's versatility and suitability for practical applications make it a promising candidate for further exploration in renewable energy research.

Electronic structure with spin-orbit coupling effect of HfH molecule for laser cooling investigations

The electronic structure, including the spin–orbit coupling effect of the HfH molecule, has been studied to determine if it can be cooled through Doppler and Sysphus laser cooling techniques. The multi-reference configuration interaction plus Davidson correction (MRCI + Q) method has been used to calculate its potential energy curves (P.E.C.s) in the Ω(±) and 2s+1Ʌ(+/-) representation. The spectroscopic constants Te, Re, ωe, Be, αe, the dipole moment µe, and the dissociation energies De agree very well with previously published work. In addition, we present in this work twenty new doublet and quartet states in the Ω(±) representation. The electronic transition dipole moment curves (TDMCs) between the lowest-lying electronic states have been investigated for the Δ - Π, Π - ∑+ and Δ - Φ transitions among specific Ω(±) states. The Franck-Condon factors (FCFs), the Einstein coefficient of spontaneous emission Aν′ν, and the radiative lifetime τ have been computed for the investigated transitions. In addition, properties of the molecules' electronic and vibrational states, such as the static dipole moment curves (D.M.C.s), the ionic character fionic, and the rovibrational constants are calculated. We deduce from our results that the HfH molecule is indeed a laser-cooling candidate that can reach a temperature as low as the nK regime. We present a complementary scheme with suitable experimental parameters. These results can be of great interest to experimental spectroscopists interested in ultracold diatomic molecules and their applications.

Multiband [formula omitted] theory for monolayer AsP: Symmetry, strain and spin-orbit coupling

Multiband k∙p model have been constructed for the monolayer AsP. Six conductance and six valence bands are included capable of describing the energy band dispersion, spin-orbit coupling, and strain effect, in good agreement with the first-principle results. Spin-orbit coupling strength has been confirmed. Interestingly, even when applying a small strain, the valence bands show enormous change. The competition between the valence bands causes such behavior and can be fully understood by simple formulas derived through our k∙p theory. This k∙p theory provides a simple and convenient way to understand and manipulate the optical and transport properties of monolayer AsP and their nanostructures by strain and external fields. AsP is a typical compound of a new family of two-dimensional group-VA materials, our k∙p theory can be easily extended to understand the other compounds of this material family.

Effect of anisotropic spin-orbit coupling on condensation and superfluidity of a two-dimensional Fermi gases

Effect of anisotropic spin-orbit coupling on condensation and superfluidity of a two-dimensional Fermi gases

Magnetization direction-controlled topological band structure in TlTiX (X = Si, Ge) monolayers

The quantum anomalous Hall (QAH) insulator is a vital material for the investigation of emerging topological quantum effects, but its extremely low working temperature limits experiments. Apart from the temperature challenge, effective regulation of the topological state of QAH insulators is another crucial concern. Here, by first-principles calculations, we find a family of stable two-dimensional materials TlTiX (X = Si, Ge) are large-gap QAH insulators. Their extremely robust ferromagnetic (FM) ground states are determined by both the direct- and super-exchange FM coupling. In the absence of spin–orbit coupling (SOC), there exist a spin-polarized crossing point located at each K and Kʹ points, respectively. The SOC effect results in the spontaneous breaking of C 2 symmetry and introduces a mass term, giving rise to a QAH state with sizable band gap. The tiny magnetocrystalline anisotropic energy (MAE) implies that an external magnetic field can be easily used to align magnetization deviating from z direction to the x–y plane, thereby leading to a transformation of the electronic state from the QAH state to the Weyl half semimetals state, which indicate monolayers TlTiX (X = Si, Ge) exhibit a giant magneto topological band effect. Finally, we examined the impact of stress on the band gap and MAE, which underlies the reasons for the giant magneto topological band effect attributed to the crystal field. These findings present novel prospects for the realization of large-gap QAH states with the characteristic of easily modifiable topological states.

Study of dielectric polarization and electrical transport in Bi1·2Sb0·8Te0·4Se2.6 nanofilms

Studying the dielectric response of topological insulators (TIs) can unveil their unique physical mechanisms such as charge transport and spin-orbit coupling effects. However, due to the manifestation of material's topological nature and band structure primarily in nanofilm, such thickness poses challenges for dielectric testing. To date, research on TI dielectric aspects remains relatively unexplored. Therefore, this paper successfully synthesizes nanofilm of quaternary topological insulator Bi1·2Sb0·8Te0·4Se2.6 (BSTS) using laser molecular beam epitaxy (LMBE) technique. Utilizing a wide-frequency dielectric spectrometer and a comprehensive physical properties measurement system (PPMS), we measured and thoroughly analyzed the dielectric polarization and charge transport characteristics of BSTS. We observed various polarization responses in the frequency range of 101–103 Hz, with the dipole orientation gradually failing to keep pace with the frequency increase in the range of 103–105 Hz, and the relaxation polarization unable to establish itself in the range of 105–107 Hz, with polarization primarily contributed by displacement polarization. Subsequently, we further analyzed the dependence of BSTS dielectric polarization response on temperature and film thickness, which will help reveal the influence of external factors on TI dielectric response, providing crucial insights for controlling TI materials' dielectric response. This not only deepens our understanding of the fundamental physical properties of this novel material but also offers important scientific basis and technological support for its applications in quantum computing, photonics, spintronics, and other fields.

Effects of Rashba and Dresselhaus spin-orbit couplings on the critical temperature and paramagnetic limiting field of superconductors with broken inversion symmetry

Transition temperature (Tc) and paramagnetic limiting of a superconductor without spatial inversion symmetry in the presence of both Rashba and Dresselhaus antisymmetric spin-orbit couplings is studied. The critical temperature is derived for anisotropy of the superconducting order parameter, ranging from isotropic s-wave to any pairing state with nonzero angular momentum and mixed parity singlet-triplet states emerge due to spin-orbit coupling (SOC). It will be shown that for unprotected odd parity pairing, pure Rashba and Dresselhaus SOCs have similar effects on the reduction of Tc and for combined effects of the two spin-orbit couplings at fixed SOC, Tc reduced by increasing Dresselhaus component and decreased down to its minimum value in the equal-Rashba-Dresselhaus case. The paramagnetic limiting is also analyzed for spin-singlet pairing and it is shown that the low temperature divergence behavior of paramagnetic limiting is less affected by both Rashba and Dresselhaus SOCs but for fixed SOC strength by increasing Dresselhaus component the paramagnetic limiting field is increased.

Characterization of low-lying electronic states of diatomic sodium bismuthide cation including the spin-orbit coupling effect

We present a high-level ab initio investigation of the diatomic sodium bismuth (NaBi+), which is a hitherto experimentally unknown species. The explicitly correlated multireference configuration interaction method is used to calculate energy points of thirteen low-lying Λ-S electron states associated with five dissociation limits. Detailed information on structural features, electronic characters, and spectroscopic constants is acquired. Our calculated relative energies between each of the interested higher dissociation limits and the lowest one for NaBi+, as well as splittings of energy levels for Bi, agree well with experimental data. Besides, we have identified and discussed the transition properties of bands from excited Ω states to the ground one, including transition dipole moments, Einstein coefficients, Franck-Condon factors, vibrational branching ratios, and radiative lifetimes. The extent of perturbations originating from the spin-orbit coupling effect to the present species is quantified through discussions on term values of spin-orbit matrix elements, and the spin-orbit coupling effect is proved to have introduced a significant effect to the low-lying electronic states of NaBi+.

Induced out-of-plane piezoelectricity and giant Rashba spin splitting in Janus WSiZ3H (Z = N, P, As) monolayers toward next-generation electronic devices

Two-dimensional (2D) piezoelectric nanomaterials have widely been studied recently due to their promise for various applications in technology. Investigation of vertical piezoelectricity will contribute to a deeper understanding of the intrinsic mechanism of piezoelectric effects in the 2D structures. In this paper, we report a first-principle study for the structural, electronic, piezoelectric, and transport properties of new-designed Janus WSiZ3H (Z= N, P, and As) monolayers. The structural stability of WSiZ3H is theoretically confirmed based on the energetic, phonon dispersion, and also elastic analyses. At the ground state, while WSiN3H is an indirect semiconductor, both WSiP3H and WSiAs3H are predicted to be direct semiconductors with smaller bandgaps. When the spin-orbit coupling effects are taken into account, a large valley spin splitting is observed at the K point of WSiZ3H materials. Interestingly, a giant Rashba spin splitting is found in WSiP3H and WSiAs3H with Rashba constant αR up to 770.91 meV Å. Additionally, our first-principles study indicates that Janus WSiZ3H monolayers are piezoelectric semiconductors with high out-of-plane piezoelectric coefficient |d31|, up to 0.15 pm/V, due to the broken mirror symmetry. Besides, with high electron mobilities and also possessing direct band gaps, WSiP3H and WSiAs3H monolayers are favorable for applications in optoelectronics.

Effects of Pd atom vibration in the Sr–Te octahedral interstitial space in Zintl compound SrPdTe on lattice anharmonicity and thermoelectric properties

Based on first-principles calculations, the current study deeply explores the thermoelectric properties of the Zintl compound SrPdTe. We found that the anharmonic vibration of Pd atoms plays an important role in the quartic anharmonic effect and the temperature dependence of the thermal conductivity. In the crystalline structure, Sr atoms form octahedra with eight surrounding Te atoms, while Pd atoms are located in the gaps between the octahedra. This structure makes the strong atomic mean square displacement of Pd atoms the main factor leading to the ultralow thermal conductivity. The study also reveals the effects of phonon frequency renormalization and four-phonon scattering on heat transfer performance. Even considering the spin–orbit coupling effect, multiple secondary valence band tops maintain the power factor of the material at high temperatures, providing a potential opportunity for achieving excellent thermoelectric performance.

Band Gap Alteration of Halide Mixing in Hybrid Perovskites: A First-Principles Study with Statistical Analysis.

Despite numerous studies on the band gap of three-dimensional halide perovskites using the first-principles calculations, there are still significant discrepancies between theoretical and experimental values. Various solutions have been proposed, such as employing a system-specific hybrid functional with varying degrees of exact exchange and explicitly incorporating spin-orbit coupling effects. Our research involved a comprehensive investigation of three typical lead-containing three-dimensional perovskites MAPbI3, MAPbBr3, and MAPbCl3 (MA = CH3NH3). Through a statistical analysis comparing mean absolute error (MAE) with experimental results, we demonstrated that the nonlocal van der Waals (vdW) density functional corrections (i.e., optB86b) yielded the most approximate lattice parameters in comparison to experimental values. Furthermore, based on these lattice parameters, the HSE06 hybrid functional is the optimal estimation of the band gap among all the options. Moreover, we investigated three sets of mixed three-dimensional halide perovskites by varying the halide component. This exploration contributes to the identification of MAPb(Br0.333I0.667)3 and MAPb(Cl0.333I0.667)3 as exhibiting the smallest band gap of 1.315 (1.867) eV and 1.313 (1.885) eV for PBE (HSE06), respectively. These band gaps were determined using the HSE06 method with the optimized lattice by PBE considering the optB86b corrections. The approach employed in this work produced a band gap trend closely aligned with experimental observations, underscoring the importance of adopting a reliable and material-independent computational strategy when screening new halide perovskite materials for optoelectronic applications.

Pressure-Induced Topological Phase Transition and Large Rashba Effect in Halide Double Perovskite.

In general, hydrostatic pressure can suppress ferroelectric polarization and further reduce Rashba spin-splitting, considering the spin-orbit coupling effect. Here, we present the design of ferroelectric double perovskite Cs2SnSiI6, which exhibits the anomalous enhancement of Rashba spin-splitting parameters by pressure-induced ferroelectric topological order. The Rashba effect is nonlinear with the decrease in polarization under pressure and reaches a maximum at the pressure-induced Weyl semimetal (WSM) state between the transition from a normal insulator (NI) to a topological insulator (TI). Furthermore, we discover that controlling ferroelectric polarization with an electric field can also induce the topological transition with a large Rashba spin-splitting but under a lower critical pressure. These discoveries show a tunable gaint Rashba effect and pressure-induced topological phase transition for Cs2SnSiI6, which can promote future research on the interaction between the Rashba effect and topological order, and its application to new electronic and spintronic devices.

Compact gap solitons and compact edge states of exciton–polariton condensates with spin–orbit coupling in a one-dimensional flatband lattice

We propose that the compact gap solitons and compact edge states can be excited in a flatband of the incoherently-pumped exciton–polariton condensate under a one-dimensional periodic potential lattice. The combined effects of spin–orbit coupling and periodic potential depth on the flatband structures are investigated. Then how the compact gap solitons and edge states are localized and extended inside only a fraction of a single lattice site will be studied with varying pump strengths, pump spot-sizes as well as energy detuning.