Rashba Parameters Research Articles

Strain-Induced Antiferroelectric-Ferroelectric-Antiferroelectric Phase Transitions in Epitaxial LaTaO4 Films.

We employed first-principles to delve into the strain-induced structural phase transitions in epitaxial LaTaO4 films. The ground state of bulk LaTaO4 adopts a monoclinic antiferroelectric phase, characterized by the antiphase rotation of two adjacent oxygen octahedra layers. Under epitaxial tensile strain, LaTaO4 thin films undergo a consecutive phase transition, namely, antiferroelectric-ferroelectric-antiferroelectric phase transitions. The ferroelectricity in the orthorhombic phase under tensile strain originates from the in-phase rotation of two adjacent oxygen octahedra layers, in contrast to the case of perovskite systems, in which octahedra rotation suppresses the conventional proper ferroelectricity. With spin-orbit coupling effects, a pronounced Rashba effect at the Brillouin zone center naturally leads to the formation of opposite directions of spin texture. Moreover, the tensile strain also synergistically enhances the corresponding Rashba parameters. Our findings may provide novel insights for controlling oxygen octahedra rotation to achieve control over the ferroelectricity and Rashba effect, which holds promising implications for applications in electronics and spintronics.

Spin-orbit coupling effects in single-layer phosphorene

The electronic band structure of monolayer phosphorene is thoroughly studied by considering the presence of spin-orbit interaction. We employ a multiorbital Slater-Koster tight-binding approach to derive effective k·p-type Hamiltonians that describes the dominant spin-orbit coupling (SOC) effects of the Rashba and intrinsic origin at the high Γ and S high symmetry points in phosphorene. In the absence of SOC effects a minimal admixture of pz and py atomic orbitals suffices to reproduce the well-known anisotropy of highest valence and the lowest conduction bands at the Γ point, consistent with density functional theory (DFT) and k·p methods. In contrast, the inclusion of the px and s atomic orbitals are rather crucial for an adequate description of the SOC effects in phosphorene at low energies, particularly at the S point. We introduce useful analytical expressions for the Rashba and intrinsic SOC parameters in terms of the relevant Slater-Koster integrals. In addition, we report simple formulas for the interband dipole strengths, revealing the nature of the strong anisotropic behavior of its lower bands. Our findings can be useful for further studies of electronic and spin transport properties in monolayer phosphorene and its nanoribbons. Published by the American Physical Society 2024

Rashba spin-splitting and spin Hall effect in Janus monolayers Sb2XSX’ (X, X’= S, Se, or Te; X ≠ X’)

The combined influence of spin–orbit coupling and spatial inversion asymmetry leads to an enhancement of electronic properties, including Rashba spin-splittings as well as spin Hall effect. Recent research has shown the possibility to create two-dimensional Janus materials with inherent structural asymmetry. In this work, the structural stability, piezoelectricity, electronic properties, and intrinsic spin Hall conductivity of quintuple-layer atomic Janus Sb2XSX’ (X, X’ = S, Se, Te; X ≠ X’) monolayers are investigated using first-principles calculations within the framework of density functional theory. They demonstrate relatively high in-plane piezoelectric coefficients (d22) and also possess out-of-plane piezoelectric coefficients (d31), which is due to the breaking of inversion symmetry in the crystal structure with the space group P3m1. Large Rashba parameters are obtained in Janus Sb2XSX’ monolayers, especially high for Sb2S2Te (1.62 eV Å) and Sb2SeSTe (1.33 eV Å) due to strong spin–orbit coupling. Moreover, Rashba-like spin-splitting is also observed in the edge-states as well, which is highest for Sb2SeSTe with 2.17 eV Å. Furthermore, Sb2S2Te and Sb2SeSTe monolayers reveal a significantly high Berry curvature (65.59 and 61.05 Bohr2), spin Berry curvature (−118.4 and −120.6 Bohr2), and spin Hall conductivity (1.8 and 1.6 e2/h). Our results suggest that Janus Sb2S2Te and Sb2SeSTe monolayers could be an excellent platform for multifunctional electronic applications.

Observing magnetoanisotropic weak antilocalization in near-surface quantum wells

We investigate the effects of an in-plane magnetic field on the weak antilocalization signature of near-surface quantum wells lacking bulk and inversion symmetry. The measured magnetoconductivity, which is conductivity as a function of the out-of-plane magnetic field, exhibits a strong anisotropy with respect to the direction of the in-plane magnetic field. The twofold symmetry of the observed magnetoanisotropy originates from the competition between Rashba and Dresselhaus spin-orbit couplings. The high sensitivity of the weak antilocalization to the spin texture produced by the combined Zeeman and spin-orbit fields results in very large anisotropy ratios, reaching 100%. Using a semiclassical universal model in quantitative agreement with the experimental data, we uniquely determine the values of the Dresselhaus and Rashba parameters as well as the effective in-plane g-factor of the electrons. Understanding these parameters provides prospects for different applications ranging from spintronics to topological quantum computing. Published by the American Physical Society 2024

Strong Rashba parameter of two-dimensional electron gas at CaZrO3/SrTiO3 heterointerface

We synthesized a CaZrO3/SrTiO3 oxide heterostructure, which can serve as an alternative to LaAlO3/SrTiO3, and confirmed the generation of 2-dimensional electron gas (2-DEG) at the heterointerface. We analyzed the electrical-transport properties of the 2-DEG to elucidate its intrinsic characteristics. Based on the magnetic field dependence of resistance at 2 K, which exhibited Weak Anti-localization (WAL) behaviors, the fitted Rashba parameter values were found to be about 12–15 × 10–12 eV*m. These values are stronger than the previous reported Rashba parameters obtained from the 2-DEGs in other heterostructure systems and several layered 2D materials. The observed strong spin–orbit coupling (SOC) is attributed to the strong internal electric field generated by the lattice mismatch between the CaZrO3 layer and SrTiO3 substrate. This pioneering strong SOC of the 2-DEG at the CaZrO3/SrTiO3 heterointerface may play a pivotal role in the developing future metal oxide-based quantum nanoelectronics devices.

Computation insights of MoS2-CrXY (X≠Y[dbnd]S, Se, Te) van der waals heterostructure for Spintronic and photocatalytic water Splitting applications

van der Waals heterostructure (vdWH) is an attractive technique to enhance the behavior of two-dimensional materials for designing viable products for electronic, spintronics and clean energy source application. Inspired by the recent synthesized of CrSSe monolayer, we have calculated the structural, electronic, Rashba parameters and photocatalytic properties of MoS2-CrXY (X≠YS, Se, Te) vdWH by using density functional theory calculation. Two different model of MoS2-CrXY (X≠YS, Se, Te) vdWH are presented due to the alternative order of chalcogen atom attached to MoS2 layer. Phonon band structure, thermal stability and binding energies confirms, the most favorable stacking configuration is dynamically, thermal and energetically feasible. Indirect type-I (MoS2-CrXY (X≠YS, Se)) and type-II (MoS2–CrSeTe) band alignment are observed in understudy vdWH. Large Rashba spin splitting is observed in model 2. Electrostatic potential and Bader charge analysis show charges are transferred from MoS2 layer to CrXY layer, while the potential drop separate charge carrier (holes and electrons) at the interface. Work function and charge density difference are also calculated and presented. A red shift is observed in the position of excitonic peaks from model 1 to model 2. In last we investigated the performance of these vdWH for photocatalytic water splitting at pH = 0. Our results shows that MoS2-CrXY (X≠YS, Se, Te) vdWH may be promising for future nanoelectronics, spintronics and photocatalytic water splitting.

Ab initio investigation of Bi/BaTiO3 and Bi/PbTiO3 heterostructures for spintronic applications

In this work, by means of density functional theory we investigated Bi/BaTiO3 and Bi/PbTiO3 film heterostructures, which were expected to have spin-orbit splitting of the Rashba type. Due to the electron density gradient at the interfaces in these heterostructures, a current vortex arose associated with the electron spins. Structural and electronic properties of these systems are presented, in particular, band structures were calculated considering the spin-orbit interaction, and the values of the Rashba parameters characterizing the values of the spin-orbit splitting were extracted. An impact of interfacial contact layers and ferroelectric polarization onto the Rashba parameter values is analyzed.

Hexagonal warping effect in the Janus group-VIA binary monolayers with large Rashba spin splitting and piezoelectricity.

In this paper, the electronic band structure, Rashba effect, hexagonal warping, and piezoelectricity of Janus group-VIA binary monolayers STe2, SeTe2, and Se2Te are investigated based on density functional theory (DFT). Due to the inversion asymmetry and spin-orbit coupling (SOC), the STe2, SeTe2 and Se2Te monolayers exhibit large intrinsic Rashba spin splitting (RSS) at the Γ point with the Rashba parameters 0.19 eV Å, 0.39 eV Å, and 0.34 eV Å, respectively. Interestingly, based on the k·p model via symmetry analysis, the hexagonal warping effect and a nonzero spin projection component Sz arise at a larger constant energy surface due to nonlinear k3 terms. Then, the warping strength λ was obtained by fitting the calculated energy band data. Additionally, in-plane biaxial strain can significantly modulate the band structure and RSS. Furthermore, all these systems exhibit large in-plane and out-of-plane piezoelectricity due to inversion and mirror asymmetry. The calculated piezoelectric coefficients d11 and d31 are about 15-40 pm V-1 and 0.2-0.4 pm V-1, respectively, which are superior to those of most reported Janus monolayers. Because of the large RSS and piezoelectricity, the studied materials have great potential for spintronic and piezoelectric applications.

Theoretical insight of origin of Rashba-Dresselhaus effect in tetragonal and rhombohedral phases of BiFeO3.

The inclusion of the spin-orbit coupling effect in ferroelectric materials with non-centrosymmetry leads to intriguing properties for spintronic applications. In the present work, a comparative study of spin splitting in the bulk electronic energy bands of the tetragonal and rhombohedral phases of BiFeO3 (BFO) in terms of the Rashba and Dresselhaus effects is carried out through first-principles calculations. The obtained spin splittings, particularly at the conduction band minima, are further supplemented with an effective k·p model analysis. For the tetragonal BFO, a dominating pure bulk-type Rashba effect with helical in-plane spin components shown through diagrams is observed, whereas the rhombohedral BFO shows a significant contribution from the out-of-plane spin components and an interplay between the Rashba and Dresselhaus effects is discussed. In addition, tunability of the Rashba parameters with the application of uniaxial strain (±5%) is obtained in tetragonal BFO, in which the Rashba coefficient (αR) doubles with a compressive 5% strain, making tetragonal BFO a suitable candidate for spintronic applications. More importantly, full reversal of the in-plane spin texture is obtained for the opposite polarization states in tetragonal BFO with an activation energy barrier of 1.13 eV.

Large tunable Rashba spin splitting and piezoelectric response in Janus chromium dichalcogenide monolayers

A mirror asymmetric Janus structure induces Rashba spin splitting (RSS) and a piezoelectric response. Inspired by the recently synthesized layered material CrSSe [Yang, Shi, Wang, Yue, Zheng, Zhang, Gu, Yang, Shadike, Li, and Fu, J. Mater. Chem. A 8, 25739 (2020)], we use first-principles calculations to systematically study the Rashba effect and piezoelectricity of Janus chromium dichalcogenide monolayers $\mathrm{Cr}XY$ ($X\ensuremath{\ne}Y=\text{S,}\phantom{\rule{4.pt}{0ex}}\text{Se,}\phantom{\rule{4.pt}{0ex}}\text{Te}$), as well as their regulation with biaxial strain. Our results reveal that spin-orbit coupling (SOC) plays an important role in the electronic properties (such as the semiconductor type, RSS, and valley polarization) of a $\mathrm{Cr}XY$ monolayer. Due to the mirror symmetry break and strong SOC, the strain-free $\mathrm{Cr}XY$ exhibits large Rashba parameters. Specifically, the Rashba parameter of CrSeTe is as high as 1.23 eV \AA{}. Due to the ${\mathit{k}}^{3}$ term in the valence-band edge, the CrSeTe exhibits a strong hexagonal warping effect along with a nonzero out-of-plane spin polarization ${\mathit{S}}_{z}$, which can also be found in the CrSSe and CrSTe monolayers in the lower energy valence bands. Moreover, the Janus $\mathrm{Cr}XY$ monolayer exhibits superior intrinsic piezoelectric responses (${\mathit{d}}_{31}$ = $0.4--0.83$ pm/V), which are orders of magnitude larger than those of the $\mathrm{Mo}XY$ monolayer. Furthermore, we reveal in detail the modulation of the band structure, RSS, and piezoelectric properties with biaxial strain. Tensile strain suppresses the band gap, whereas compressive strain increases the band gap. Thus, strain engineering can effectively tune the band structures resulting in semiconductor-metal and indirect-direct transitions. In addition, the strain has opposite effects on the RSS and the piezoelectricity; that is, unlike compressive strain-enhanced RSS, the tensile strain can significantly elevate the piezoelectric coefficients. Our results indicate that a Janus $\mathrm{Cr}XY$ monolayer has coexisting large intrinsic RSS and piezoelectricity, which can be efficiently regulated by strain engineering, opening opportunities for applications in spintronic and piezoelectric devices.

Chiral electronic excitations in the quasi-two-dimensional Rashba system BiTeI

The optical transitions between spin-polarized bands of the quasi-two dimensional Rashba system BiTeI are investigated using polarization resolved resonant Raman spectroscopy. We detect chiral excitations between states with opposite helicity and compare spectra to calculations within a three-band model. Using the resonant Raman excitation profile, we deduce the Rashba parameters and band gaps of the higher conduction bands near the Fermi level, and compare the parameters to values obtained by ab initio density function theory (DFT).

Scaling law for Rashba-type spin splitting in quantum-well films

We use laser-based spin- and angle-resolved photoemission spectroscopy (laser-SARPES) with high resolution and experimentally determine, for the first time, the Rashba parameters of quantum-well states (QWSs) systematically changing with the film thickness and the quantum numbers, through the observation of the Ag films grown on an Au(111) substrate. The data are very well reproduced by the theoretical calculations based on the density functional theory. Most importantly, we find a scaling law for the Rashba parameter (${\ensuremath{\alpha}}_{\mathrm{R}}$) that the magnitude of ${\ensuremath{\alpha}}_{\mathrm{R}}$ is scaled by the charge density at the interface and the spin-orbit coupling ratio between the film and the substrate, and it is expressed by a single straight line regardless of the film thickness and the quantum numbers. The new finding not only is crucial to understand the Rashba effect in QWSs but also gives a foundation of film growth engineering to fine-tune the spin splitting in 2D heterostructure systems.

First-principle studies on the ferroelectricity and gate-controlled Rashba spin-orbit coupling of d1T-phase transition-metal dichalcogenide monolayers

Two-dimensional ferroelectric Rashba semiconductors exhibit extraordinary orbital and spin structures. In this research, through first-principle calculations, we demonstrate the ferroelectricity of d1T-phase (distorted 1T-phase) transition-metal dichalcogenide monolayers and realize the manipulation of the Rashba spin-orbit coupling by means of gate voltage. Because of its large composition of out-of-plane atomic orbitals, the rotation of transition metal atoms induced symmetry breaking leads to larger Rashba spin splittings at Γ point of top valence band (560.4 meV Å for WS 2 , measured by the first derivative of the energy splitting to the wave vector), and it further increases under a vertical downward electric field and hole doping, which correspond to a positive gate voltage for the constructed device. In comparison, charge doping has a greater effect on Rashba parameters than electric field. These results are of great value to the spin-orbit electronics of two-dimensional materials and their applications in electrically controlled spintronics and memory devices. • The ferroelectricity and Rashba SOC of monolayer d1T-phase TMDs are demonstrated. • The Rashba parameter is evaluated by the first derivative of the energy splitting. • One factor of greater Rashba strength is larger vertical orbital composition. • Another origin is the gradient of potential energy affected by charge transfer. • The strength is tuned linearly by electric field and nonlinearly by charge doping.

Effect of magnons on the temperature dependence and anisotropy of spin-orbit torque

We investigate the influence of magnons on the temperature-dependence and the anisotropy of the spin-orbit torque (SOT). For this purpose we use 3rd order perturbation theory in the framework of the Keldysh formalism in order to derive suitable equations to compute the magnonic SOT. We find several contributions to the magnonic SOT, which depend differently on the spin-wave stiffness $\mathcal{A}$ and on the temperature $T$, with the dominating contribution scaling like $T^{2}/\mathcal{A}^{2}$. Based on this formalism we compute the magnonic SOT in the ferromagnetic Rashba model. For large Rashba parameters the magnonic SOT is strongly anisotropic and for small quasiparticle broadening it may become larger than the non-magnonic SOT.

Intertwined nontrivial band topology and giant Rashba spin splitting

Composite quantum compounds (CQCs) have become an important avenue for the investigation of intercorrelation between two distinct phenomena in physics. Topological superconductors, axion insulators, etc., are a few such CQCs which have recently drawn tremendous attention in the community. Topological nontriviality and Rashba spin physics are two different quantum phenomena but can be intertwined within a CQC platform. In this paper, we present a general symmetry-based mechanism, supported by ab initio calculations, to achieve intertwined giant Rashba splitting and topological nontrivial states simultaneously in a single crystalline system. Such coexistent properties can further be tuned to achieve other rich phenomena. We have achieved Rashba splitting energy ($\mathrm{\ensuremath{\Delta}}E$) and Rashba coefficient ($\ensuremath{\alpha}$) values as large as 161 meV and 4.87 eV \AA{}, respectively, in conjunction with the Weyl semimetal phase in ${\mathrm{KSnSb}}_{0.625}{\mathrm{Bi}}_{0.375}$. Interestingly, these values are even larger than the values reported for the widely studied topologically trivial Rashba semiconductor BiTeI. The advantage of our present analysis is that one can achieve various topological phases without compromising the Rashba parameters, within this CQC platform.

Spin Precession and Spin‐Charge Conversion in a Strong Rashba Channel at Room Temperature

The detection of spin current injected from the ferromagnet source to the semiconductor channel is very challenging due to the low injection efficiency at the interface. Especially, it is difficult to detect the spin precession signal in a strong Rashba system without a signal decay. In a semiconductor system, the spin Hall angle is much larger than the spin injection efficiency, so the spin Hall effect is utilized for room temperature operation of the semiconductor-based Rashba devices. To realize spin transport device induce by the spin-charge and charge-spin conversions, the direct spin Hall effect (DSHE) and the inverse spin Hall effect (ISHE) are adopted, respectively. The spin current is clearly detected up to room temperature and the spin transport signal agrees to the temperature dependence of the Rashba effect. From these spin transport signals, we suggest another option to extract Rashba parameters from cryogenic temperature to room temperature. The both signals of DSHE and ISHE also confirm the Onsager Reciprocity in a Rashba system.

Switchable Rashba anisotropy in layered hybrid organic\u2013inorganic perovskite by hybrid improper ferroelectricity

Hybrid organic–inorganic perovskites (HOIPs) are introducing exotic directions in the photovoltaic materials landscape. The coexistence of inversion symmetry breaking and spin–orbit interactions play a key role in their optoelectronic properties. We perform a detailed study on a recently synthesized ferroelectric layered HOIP, (AMP)PbI4 (AMP = 4-aminomethyl-piperidinium). The calculated polarization and Rashba parameters are in excellent agreement with experimental values. Moreover, we report a striking effect, i.e., an extraordinarily large Rashba anisotropy that is tunable by ferroelectric polarization: as polarization is reversed, not only the spin texture chirality is inverted, but also the major and minor axes of the Rashba anisotropy ellipse in k-space are interchanged—a pseudo rotation. A k·p model Hamiltonian and symmetry-mode analysis reveal a quadrilinear coupling between the cation-rotation modes responsible for the Rashba ellipse pseudo-rotation, the framework rotation, and the polarization. These findings may provide different avenues for spin-optoelectronic devices such as spin valves or spin FETs.

High-harmonic generation in spin-orbit coupled systems

We study high-harmonic generation in two-dimensional electron systems with Rashba and Dresselhaus spin-orbit coupling and derive harmonic generation selection rules with the help of group theory. Based on the bandstructures of these minimal models and explicit simulations we reveal how the spin-orbit parameters control the cutoff energy in the high-harmonic spectrum. We also show that the magnetic field and polarization dependence of this spectrum provides information on the magnitude of the Rashba and Dresselhaus spin-orbit coupling parameters. The shape of the Fermi surface can be deduced at least qualitatively and if only one type of spin-orbit coupling is present, the coupling strength can be determined.

One-dimensional Rashba states in Pb atomic chains on a semiconductor surface

We investigate the electronic and spin structure of Pb atomic chains on a $\mathrm{Si}(100)\ensuremath{-}2\ifmmode\times\else\texttimes\fi{}1$ surface using first-principles calculations. We revealed that the electronic spectra of linear dimerized Pb chains with orientations perpendicular and parallel to the Si dimers are characterized by one-dimensional large Rashba spin splitting providing exclusive spin polarization of the carriers that makes these systems suitable for studying the spin-transport phenomena and realizing a tunable spin current. A buckled dimerized Pb chain with a parallel orientation was predicted to be an insulating Rashba system with a vortical spin texture and asymmetric charge distribution. In this paper we trace the origin of Rashba band anisotropy and its interplay with chain geometry. The Rashba parameters of the considered chains are compared with other well-known systems.

Ultrafast Control of Excitonic Rashba Fine Structure by Phonon Coherence in the Metal Halide Perovskite CH_{3}NH_{3}PbI_{3}.

We discover hidden Rashba fine structure in CH_{3}NH_{3}PbI_{3} and demonstrate its quantum control by vibrational coherence through symmetry-selective vibronic (electron-phonon) coupling. Above a critical threshold of a single-cycle terahertz pump field, a Raman phonon mode distinctly modulates the middle excitonic states with persistent coherence for more than ten times longer than the ones on two sides that predominately couple to infrared phonons. These vibronic quantum beats, together with first-principles modeling of phonon periodically modulated Rashba parameters, identify a threefold excitonic fine structure splitting, i.e., optically forbidden, degenerate dark states in between two bright ones with a narrow, ∼3 nm splitting. Harnessing of vibronic quantum coherence and symmetry inspires light-perovskite quantum control and sub-THz-cycle "Rashba engineering" of spin-split bands for ultimate multifunction device.