Dresselhaus Spin-orbit Coupling Research Articles

Controllable quantum scars induced by spin–orbit couplings in quantum dots

Spin–orbit couplings (SOCs), originating from the relativistic corrections in the Dirac equation, offer nonlinearity in the classical limit and are capable of driving chaotic dynamics. In a nanoscale quantum dot confined by a two-dimensional parabolic potential with SOCs, various quantum scar states emerge quasi-periodically in the eigenstates of the system, when the ratio of confinement energies in the two directions is nearly commensurable. The scars, displaying both quantum interference and classical trajectory features on the electron density, due to relativistic effects, serve as a bridge between the classical and quantum behaviors of the system. When the strengths of Rashba and Dresselhaus SOCs are identical, the chaos in the classical limit is eliminated as the classical Hamilton’s equations become linear, leading to the disappearance of all quantum scar states. Importantly, the quantum scars induced by SOCs are robust against small perturbations of system parameters. With precise control achievable through external gating, the quantum scar induced by Rashba SOC is fully controllable and detectable.

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.

Laser-field-mediated Rashba and Dresselhaus spin–orbit control in GaInAs/AlInAs quantum wells

For more possibilities in exploring the spin–orbit (SO) control in two-dimensional (2D) semiconductor quantum wells, we resort to the laser field by constructing a generic model including both the axial and transverse field components relative to the well-growth direction, with the axial one primarily modifying the structural potential of the well and the transverse one mainly altering the electron density of states and so the Hartree potential. For GaInAs/AlInAs quantum wells with two-subband occupation, we obtain the full scenario of the laser-field response of the Rashba and Dresselhaus SO couplings, including both the intrasubband (αν and βν with ν = 1,2 denoting the subband index) and intersubband (η and Γ) types, by solving the Poisson–Schrödinger equations. Remarkably, for the Dresselhaus coupling, which is insensitive to the electrical manipulation, we demonstrate that it can be substantially tuned by the laser field and unified SO control of different subbands is possible, suggesting that the optical manner is an effective supplement to the electrical means. Moreover, symmetric (α1=−α2) and selective (α1=0, α2≠0) control of the Rashba coupling of different subbands are also observed with the interplay of the two laser components, which are desirable for the realization of skyrmion lattice and the suppression of spin relaxation of given subbands. Besides, for the intersubband coupling, the Rashba term η is optically tunable while the Dresselhaus term Γ is basically immune to the laser field, i.e., selective control of the intersubband coupling by virtue of optical means. These diverse laser-field-mediated SO features offer exciting possibilities in incorporating 2D quantum wells for new applications in the field of spintronics.

Prediction of superconductivity in a series of tetragonal transition metal dichalcogenides.

Transition metal dichalcogenides (TMDCs) represent a well-known material family with diverse structural phases and rich electronic properties; they are thus an ideal platform for studying the emergence and exotic phenomenon of superconductivity (SC). Herein, we propose the existence of tetragonal TMDCs with a distorted Lieb (dLieb) lattice structure and the stabilized transition metal disulfides (MS2), including dLieb-ZrS2, dLieb-NbS2, dLieb-MnS2, dLieb-FeS2, dLieb-ReS2, and dLieb-OsS2. Except for semiconducting dLieb-ZrS2 and magnetic dLieb-MnS2, the rest of metallic dLieb-MS2 was found to exhibit intrinsic SC with the transition temperature (TC) ranging from ∼5.4 to ∼13.0 K. The TC of dLieb-ReS2 and dLieb-OsS2 exceeded 10 K and was higher than that of the intrinsic SC in the known metallic TMDCs, which is attributed to the significant phonon-softening enhanced electron-phonon coupling strength. Different from the Ising spin-orbit coupling (SOC) effect in existing non-centrosymmetric TMDCs, the non-magnetic dLieb-MS2 monolayers exhibit the Dresselhaus SOC effect, which is featured by in-plane spin orientations and will give rise to the topological SC under proper conditions. In addition to enriching the structural phases of TMDCs, our work predicts a series of SC candidates with high intrinsic TC and topological non-triviality used for fault-tolerant quantum computation.

Crystallographic rotation effect on the particle and spin across a half metal/semiconductor junction with Dresselhaus spin-orbit interaction

Theoretical studies were conducted on probability, conductance and spin polarization through a junction between a half metal (HM)/semiconductor with Dresselhaus spin-orbit coupling (DSOC), using the scattering theory and the continuous model in a two-dimensional system. The focus was on how the bulk orientation of the DSOC affects the charge and spin polarization. Results showed that the crystal face (100) makes a negative perpendicular to the normal wave vector of the system, resulting in a maximum value of the conductance spectrum and the spin polarization. However, the maximum value of the spin polarization can occur with any crystallographic orientation when the applied voltage reaches the crossing point of the DSOC. Moreover, the electron incident angle injection can cause a gap between in the transmission probability with spin up and spin down, corresponding to higher charge and spin polarization across the junction.

Spin relaxation time enhancement induced by polarization field screening in an InGaN/GaN quantum well

A correlation between the spin-polarized carrier transfer and spin relaxation processes of a two-dimensional electron gas (2DEG) in an InGaN/GaN quantum well (QW) is investigated by time-resolved Kerr rotation spectroscopy at low temperature. Upon resonant excitation with the GaN barrier band edge energy, the spin polarization of the 2DEG in the QW is acquired from the transfer of spin-polarized photoexcited carriers. Significantly, the spin relaxation time of the 2DEG is enhanced to be as long as 1 ns along with the carrier transfer. It is demonstrated that by tailoring the Rashba and Dresselhaus spin–orbit couplings to approach a spin-degenerate surface, the screening effect of the polarization field leads to a longer spin relaxation time and effective manipulation of the spin relaxation. The polarization field screening induced enhancement of the spin relaxation time is significant in the way for the development of GaN-based spintronic devices.

Linear and nonlinear spin current response of anisotropic spin-orbit coupled systems

We calculate the linear and the second harmonic (SH) spin current response of two anisotropic systems with spin–orbit (SO) interaction. General expressions of wide applicability for the these response functions are first derived for a generic two-band Hamiltonian. The first system is a two-dimensional (2D) electron gas in the presence of Rashba and k-linear Dresselhaus SO couplings. The calculations show how narrow or wide the response spectra can be, what is their overall shape and size, and frequency shiftings, depending on which crystal orientation is selected. The quantitative knowing of this makes possible a comparative study for several orientations, which would allow to select a spectrum with particular characteristic. We find that vanishing linear and second order response tensors are achievable under SU(2) symmetry conditions, characterized by a collinear SO vector field. Additional conditions under which specific tensor components vanish are possible, without having such collinearity. Thus, a proper choice of the growth direction and SO strengths allows to select the polarization of the linear and SH spin currents according to the direction of flowing. The second system is an anisotropic 2D free electron gas with anisotropic Rashba interaction, which has been employed to study the optical conductivity of 2D puckered structures with anisotropic energy bands. The presence of mass anisotropy and an energy gap open several distinct scenarios for the allowed optical interband transitions, which manifest in the linear and SH response contrastingly. The linear response displays only out-of-plane spin polarized currents, while the SH spin currents flow with spin orientation lying parallel to the plane of the system strictly. The models illustrate the possibility of the nonlinear spin Hall effect in systems with SO interaction, under the presence or absence of time-reversal symmetry. The results suggest different ways to manipulate the linear and nonlinear optical generation of spin currents which could find spintronic applications.

Customizing topological phases in the twisted bilayer superconductors with even-parity pairings

We investigate the topological properties of twisted bilayer superconductors with different even-parity pairings in each layer. In the presence of spin–orbit coupling, the Hamiltonian is mapped into an effective odd-parity superconductor. Based on this, we deduce the topological properties by examining the relative configuration between Fermi surface and Dirac pairing node. We show that mixed Rashba and Dresselhaus spin–orbit coupling and anisotropic hopping terms, which break the C 4 symmetry of the Fermi surface, can induce first-order topological superconductors with non-zero bulk Chern number. This provides a versatile way to control the topological phases of bilayer superconductors by adjusting the twisted angle and chemical potential. We demonstrate our results using a typical twisted angle of 53.13°, at which the translation symmetry is restored and the Chern number and edge state are calculated using the Moiré momentum.

Compacton existence and spin-orbit density dependence in Bose-Einstein condensates.

We demonstrate the existence of compactons matter waves in binary mixtures of Bose-Einstein condensates (BEC) trapped in deep optical lattices (OL) subjected to equal contributions of intraspecies Rashba and Dresselhaus spin-orbit coupling (SOC) under periodic time modulations of the intraspecies scattering length. We show that these modulations lead to a rescaling of the SOC parameters that involves the density imbalance of the two components. This gives rise to density dependent SOC parameters that strongly influence the existence and the stability of compacton matter waves. The stability of SOC-compactons is investigated both by linear stability analysis and by time integrations of the coupled Gross-Pitaevskii equations. We find that SOC restricts the parameter ranges for stable stationary SOC-compacton existence but, on the other side, it gives a more stringent signature of their occurrence. In particular, SOC-compactons should appear when the intraspecies interactions and the number of atoms in the two components are perfectly balanced (or close to being balanced for the metastable case). The possibility to use SOC-compactons as a tool for indirect measurements of the number of atoms and/or the intraspecies interactions is also suggested.

Tuning spin-orbit coupling and realizing inverse persistent spin helix by an extra above-barrier radiation in a GaAs/Al0.3Ga0.7As heterostructure.

A persistent spin helix with equal strength of the Rashba and Dresselhaus spin-orbit coupling (SOC) is expected for future spintronic devices due to the suppression of spin relaxation. In this work we investigate the optical tuning of the Rashba and Dresselhaus SOC by monitoring the spin-galvanic effect (SGE) in a GaAs/Al0.3Ga0.7As two dimensional electron gas. An extra control light above the bandgap of the barrier is introduced to tune the SGE excited by a circularly polarized light below the bandgap of GaAs. We observe different tunability of the Rashba- and Dresselhaus-related SGE currents and extract the ratio of the Rashba and Dresselhaus coefficients. It decreases monotonously with the power of the control light and reaches a particular value of ∼-1, implying the formation of the inverse persistent spin helix state. By analyzing the optical tuning process phenomenologically and microscopically, we reveal greater optical tunability of the Rashba SOC than that of the Dresselhaus SOC.

Polaron induced local spin texture and anomalous Hall effect in the quadrilateral prism-shaped nanotube with Rashba and Dresselhaus spin–orbit coupling

We theoretically study the spin-texture dynamics and the transverse asymmetric charge deflection induced by the polaron in a quadrilateral prism-shaped nanotube with the Rashba and Dresselhaus spin–orbit coupling (SOC). We reveal the polaron gives rise to the nontrivial local spin textures in the nanotube within the cross section plane. The spins demonstrate oscillations and the oscillating patterns are dependent on the SOC type. For the nanotube containing a segment of the ferromagnetic domain, the sizable asymmetric charge deflections could additionally take place, namely, the anomalous Hall effect. The amount of the deflected charges is determined by the strength and orientations of the ferromagnetic magnetization as well as the SOC type. The work provides a valuable insight of the coherent transport of polaron through a quasi-one-dimensional nanotube with Rashba and Dresselhaus SOC and open avenues for the potential device applications.

Electron-Spin Filter Based on Dresselhaus Spin-Orbit-Coupling Modulated Single-Layered Semiconductor Nanostructure

We theoretically investigate Dresselhaus spin-orbit coupling (SOC)-induced spin-polarized transport for electrons tunneling through single-layered semiconductor nanostructure (SLSN, InSb). A considerable electron-spin polarization is observed in this SLSN. Spin polarization ratio is associated with the electron energy and in-plane wave vector; in particular, it can be manipulated by the strain engineering or the layer thickness. Based on this SLSN, a controllable electron-spin filter is proposed for spintronics device applications.

Impact of the p-cubic Dresselhaus term on the spin Hall effect

It is well known that the Dresselhaus spin-orbit coupling (SOC) in semiconductor two dimensional electron gases (2DEGs) possesses both linear and cubic in momentum contributions. Nevertheless, the latter is usually neglected in most theoretical studies. However, recent Kerr rotation experiments have revealed a significant enhancement of the cubic Dresselhaus interaction by increasing the drift velocities in 2DEGs hosted in GaAs quantum wells. Here, we present a study of the optical spin Hall conductivity in 2DEGs under the simultaneous presence of Rashba and (linear plus cubic) Dresselhaus SOC. The work was done within the Kubo formalism in linear response. We show that the coexistence of the Rashba and cubic Dresselhaus SOC in 2DEGs promotes a strong anisotropy of the band spin splitting which in turn leads to a very characteristic frequency dependence of the spin Hall conductivity. We find that the spin Hall conductivity response could be very sensible to sizeable cubic-Dresselhaus coupling strength. This may be of relevance for the optical control of spin currents in 2DEGs with non-negligible cubic-Dresselhaus SOC.

Formation of the skyrmionic polaron by Rashba and Dresselhaus spin-orbit coupling

Skyrmions in reduced dimensions such as thin layers and interfaces are of both fundamental and technological importance. In these systems, itinerant electrons are often present together with the Rashba and Dresselhaus spin-orbit coupling (SOC). Here, we show that an itinerant electron in the presence of these interactions can nucleate the skyrmion state, even when the standard Dzyaloshinskii-Moriya interaction (DMI) is absent, and the electron can become self-trapped in the skyrmion core, forming the ``skyrmionic polaron'' (SkP). The formation of the SkP is investigated from a continuum model of the electron, exchange coupled to the lattice spins, by solving the appropriate Euler-Lagrange equations. The skyrmion (antiskyrmion) texture is favored by the Rashba (Dresselhaus) SOC, with the binding energy increasing quadratically with the strength of the interaction. In contrast, if the skyrmion is already formed due to a nonzero DMI, the electron is delocalized and avoids the skyrmion core until the strength of the Rashba or Dresselhaus SOC exceeds a critical value. Below this critical value, the electron is not bound to the skyrmion core, the polaron does not form, and the electron has little effect on the skyrmion state. Our work envisions the possibility of manipulating the skyrmion state in device applications by altering the strength of the Rashba or Dresselhaus interactions, e.g., by an external electric field.

Collective Spin Modes in Fermi Liquids with Spin–Orbit Coupling

A combination of spin-orbit coupling and electron-electron interaction gives rise to a new type of collective spin modes, which correspond to oscillations of magnetization even in the absence of the external magnetic field. We review recent progress in theoretical understanding and experimental observation of such modes, focusing on three examples of real-life systems: a two-dimensional electron gas with Rashba and/or Dresselhaus spin-orbit coupling, graphene with proximity-induced spin-orbit coupling, and the Dirac state on the surface of a three-dimensional topological insulator. This paper is dedicated to the 95th birthday of Professor Emmanuel I. Rashba.

Topological defects of dipolar bose-einstein condensates with dresselhaus spin-orbit coupling in an anharmonic trap

We consider the topological defects and spin structures of binary Bose-Einstein condensates (BECs) with Dresselhaus spin-orbit coupling (D-SOC) and dipole-dipole interaction (DDI) in an anharmonic trap. The combined effects of D-SOC, DDI and anharmonic trap on the ground-state phases of the system are analyzed. Our results show various structural phase transitions can be achieved by adjusting the magnitudes of the D-SOC and DDI. Meantime, a ground-state phase diagram is given as a function of the D-SOC and DDI strengths. In addition, we find that tuning the D-SOC and the DDI can derive novel rich topological configurations, including ghost vortex, half-quantum vortex, skyrmion pair, vertical skyrmion string and horizontal skyrmion string.

Conductance matrix symmetries of multiterminal semiconductor-superconductor devices

Nonlocal tunneling spectroscopy of multiterminal semiconductor-superconductor hybrid devices is a powerful tool to investigate the Andreev bound states below the parent superconducting gap. We examine how to exploit both microscopic and geometrical symmetries of the system to extract information on the normal and Andreev transmission probabilities from the multiterminal electric or thermoelectric differential conductance matrix under the assumption of an electrostatic potential landscape independent of the bias voltages, as well as the absence of leakage currents. These assumptions lead to several symmetry relations on the conductance matrix. Next, by considering a numerical model of a proximitized semiconductor wire with spin-orbit coupling and two normal contacts at its ends, we show how such symmetries can be used to identify the direction and relative strength of Rashba versus Dresselhaus spin-orbit coupling. Finally, we study how a voltage-bias-dependent electrostatic potential as well as quasiparticle leakage break the derived symmetry relations and investigate characteristic signatures of these two contributions.

Spin Hall effect in two-dimensional InSe: Interplay between Rashba and Dresselhaus spin-orbit couplings

Materials with inversion asymmetries can exhibit strong spin Hall effect (SHE) in the presence of Dresselhaus and Rashba spin-orbit coupling (D/R SOC) interactions. Ideally, in a two-dimensional crystal, inversion asymmetry could be modulated by stacking order and external perturbations. Here, using first-principles calculations, we systematically investigate the interplay between DSOC and RSOC and their influences on SHE in mono- and bilayer InSe. We show that in the presence of DSOC, the introduction of Rashba interaction through gate voltages in monolayer InSe increases Zeeman-like spin splitting around the Brillouin-zone center and contributes to the enhancement of spin Hall conductivity (SHC), which reaches a saturation point due to the RSOC-enforced spiral-spin texture. The SHC in the unperturbed centrosymmetric $\mathit{AB}$ stacked bilayer shows a peak associated with the Mexican-hat-like valence-band edge; however, in a wide energy range the SHC stays insignificant. In the $\mathit{AB}$\ensuremath{'} stacked bilayer with the intrinsic RSOC present, the value of SHC can be comparable to that of $\mathit{AB}$ stacked bilayer with an external electric field. Moreover, we show that the spin-momentum locking in the $\mathit{AB}$\ensuremath{'} stacked bilayer is switchable by a gate voltage. These findings provide a promising route for spintronic and magneto-optical applications by exploiting the rich physics of spin-orbit effects.

Superfluid transition temperature and fluctuation theory of spin-orbit- and Rabi-coupled fermions with tunable interactions

We obtain the superfluid transition temperature of equal Rashba-Dresselhaus spin-orbit- and Rabi-coupled Fermi superfluids, from the Bardeen-Cooper-Schrieffer (BCS) to Bose-Einstein condensate (BEC) regimes in three dimensions for tunable $s$-wave interactions. In the presence of Rabi coupling, we find that spin-orbit coupling enhances (reduces) the critical temperature in the BEC (BCS) limit. For fixed interactions, we show that spin-orbit coupling can convert a first-order (discontinuous) phase transition into a second-order (continuous) phase transition, as a function of Rabi coupling. We derive the Ginzburg-Landau free energy to sixth power in the superfluid order parameter to describe both continuous and discontinuous phase transitions as a function of spin-orbit and Rabi couplings. Lastly, we develop a time-dependent Ginzburg-Landau fluctuation theory for an arbitrary mixture of Rashba and Dresselhaus spin-orbit couplings at any interaction strength.

(2+1)-dimensional unstable matter waves in self-interacting pseudospin-1/2 BECs under combined Rashba and Dresselhaus spin-orbit couplings

The modulational instability (MI) of continuous waves is exclusively addressed theoretically and numerically in a two-component Bose-Einstein condensate in the presence of a mixture of Rashba and Dresselhaus (RD) spin-orbit couplings and the Lee-Huang-Yang (LHY) term. The linear stability analysis is utilized to derive an expression for the MI growth rate. It is revealed that instability can be excited in the presence of the RD spin-orbit coupling under conditions where nonlinear and dispersive effects are suitably balanced. Analytical predictions are confirmed via direct numerical simulations, where MI is manifested by the emergence of soliton-molecules that include four-peaked solitons and more exotic vortex structures that are very sensitive to variations in spin-orbit coupling strengths. Our study suggests that MI is a suitable mechanism for generating matter waves through multi-peaked solitons of various geometries.