Presence Of Rashba Spin-orbit Interaction Research Articles

Spin filtration in generalized Sierpinski triangles in presence of Rashba spin–orbit interaction

In this work, we theoretically investigate the phenomenon of spin polarization in generalized Sierpinski gasket (SPG) triangles (, , , ) in the presence of Rashba spin–orbit interaction (RSOI) within a tight-binding framework. The geometrical construction is addressed for all four types of generalized SPG triangles using an iterative function system that begins with a fixed triangle of any arbitrary side length. The geometry of various types of fractal networks has a major impact on the degeneracy of the energy spectrum. It is shown that only the two-terminal setup in the presence of RSOI is incapable of breaking the spin degeneracy, which necessitates the use of a three-terminal setup to break the time-reversal symmetry. The effect of flip map induced anisotropic hopping integrals on three-terminal spin-resolved transmission probabilities is studied. In several cases, we find almost spin polarization in our considered lattices. We also analyze how spin polarization varies with RSOI strength and fractal generations. Our results indicate that fractal lattices might be suitable functional elements for designing future spin-based electronic devices.

Solutions of Noncommutative Two-Dimensional Position–Dependent Mass Dirac Equation in the Presence of Rashba Spin-Orbit Interaction by Using the Nikiforov–Uvarov Method

Solutions of Noncommutative Two-Dimensional Position–Dependent Mass Dirac Equation in the Presence of Rashba Spin-Orbit Interaction by Using the Nikiforov–Uvarov Method

Simultaneous effects of Rashba, magnetic field and impurity on the magnetization and magnetic susceptibility of a GaAs-semiconductor quantum ring

The magnetization and magnetic susceptibility of GaAs/AlGaAs quantum ring (QR) with the presence of Rashba spin-orbit interaction and acceptor Gaussian impurity have been studied. We have used the shifted 1/N expansion to calculate the energy eigenvalues as a function of the magnetic field. The obtained energies show energy level crossings; transition in the angular momentum of the ground state of the QR. Furthermore, we investigate the dependence of energy eigenvalues of QR on: confinement potential strength, Rashba parameter, and the presence of acceptor impurity. The comparisons show that the present computed results are in a good agreement with the available experimental and theoretical ones.Furthermore, we have shown the variation of the magnetization and magnetic susceptibility with the Hamiltonian variables. These magnetic quantities show an oscillating behavior associated with the phenomena of energy level crossings. The computed results indicate that as the Rashba strength increases, the positions of these oscillating peaks in the magnetic susceptibility curve shift towards a lower magnetic field value.

Effects of impurity factor on the physical and transport properties for Ga1-xAlxAs quantum wire in the presence of Rashba spin-orbit interaction

There is a need to get familiarized with a systematic and precise approach to study the energy dispersion and ballistic conductance in a Ga1-xAlxAs quantum wire. We have employed parabolic confinement in this work. The combined impacts of Rashba spin orbit interaction (RSOI), external electric field, magnetic field, and Aluminium concentration on energy dispersion and conductivity in a Ga1-xAlxAs quantum wire have been explored. The Energy eigenvalues and eigenvectors are quantified using the diagonalization method and the transport properties are computed by Landuer-Bttiker formalism. It is noticed that the external electric field, magnetic field, Rashba spin-orbit interaction, and Aluminium concentration (impurity factor x) alter the energy spectra and conductivity. Hence, these parameters significantly affect the physical and transport properties.

Topological properties of Josephson current between two s- and p-wave superconducting nanowires with Majorana fermions

Josephson current between two one-dimensional nanowires with proximity induced either s-wave or p-wave pairing and separated by a narrow dielectric barrier is calculated in the presence of Rashba spin-orbit interaction, in-plane and normal Zeeman magnetic fields. We show that Andreev retro-tunneling is realized by means of two channels. The main contribution to the Josephson current in junction of s- or p-wave superconductors is shown to give Andreev scattering in a conventional particle-hole channel, when an electron-like quasiparticle reflects to a hole-like quasiparticle with opposite spin yielding a current which depends only on the order parameters’ phase differences φ and oscillates with fractional 4π period. Nevertheless Andreev bound state energy in second anomalous particle-hole channel, corresponding to the reflection of an incident electron-like quasiparticle to a hole-like quasiparticle with the same spin orientation, survives only in the presence of the in-plane magnetic field, and oscillates with 4π period not only with φ but also with orientational angle of the in-plane magnetic field θ resulting in a magneto-Josephson effect. In the presence of Rashba spin-orbit coupling (SOC) and normal-to-plane magnetic field h, a forbidden gap is shown to open in the dependence of Andreev bound state energies on the phases φ and θ at several values of SOC strength and magnetic field, where Josephson current seems to vanish. The magnetic fields destroy also the particle-hole symmetry of the mid-gap states around Fermi level.

Josephson current between two p-wave superconducting nanowires in the presence of Rashba spin-orbit interaction and Zeeman magnetic fields

Josephson current between two one-dimensional nanowires with proximity induced p-wave superconducting pairing is calculated in the presence of Rashba spin-orbit interaction, in-plane and normal magnetic fields. We show that Andreev retro-reflection is realized by means of two different channels. The main contribution to the Josephson current gives a scattering in a conventional particle-hole channel, when an electron-like quasiparticle reflects to a hole-like quasiparticle with opposite spin yielding a current which depends only on the order parameters’ phase differences φ and oscillates with 4π period. Second anomalous particle-hole channel, corresponding to the Andreev reflection of an incident electron-like quasiparticle to an hole-like quasiparticle with the same spin orientation, survives only in the presence of the in-plane magnetic field. The contribution of this channel to the Josephson current oscillates with 4π period not only with φ but also with orientational angle of the in-plane magnetic field θ resulting in a magneto-Josephson effect. In the presence of Rashba spin-orbit coupling (SOC) and normal-to-plane magnetic field h, a forbidden gap is shown to open in the dependence of Andreev bound state energies on the phases φ and θ at several values of SOC strength and magnetic field, where Josephson current seems to vanish. We present a detailed theoretical analysis of both DC and AC Josephson effects in such a system showing contributions from these channels and discuss experiments which can test our theory.

The effect of Rashba spin–orbit interaction on the spin-polarized transport of zigzag phosphorene nanoribbons

Spin transport features of zigzag phosphorene nanoribbons (ZPNRs) are investigated in the presence of the perpendicular electric field (), the exchange field , and Rashba spin–orbit interaction (RSOI). To this end, the non-equilibrium Green’s function method is used based on the tight-binding model, which can be described by the Landauer–Büttiker formalism. Interestingly, spin-filtering and spin-flipping are observed only for incoming up (down) spins in the presence of the exchange field with anti-parallel configuration (parallel configuration). Furthermore, changing the magnitude and direction of for the parallel and anti-parallel configurations of the exchange field in the presence of RSOI can induce and control the ON/OFF state of the current, the band gap, the spin polarization, spin-flipping, and spin-filtering in the system. The obtained results could be utilized to construct novel nanostructures and also to maximize the efficiency of spintronic devices based on ZPNRs.

Rashba spin-orbit interaction effects on thermal and magnetic properties of parabolic GaAs quantum dot in the presence of donor impurity under external electric and magnetic fields

Based on the effective mass approximation, the magnetic and thermal properties of parabolic GaAs quantum dot have been investigated in the presence of Rashba Spin-Orbit interaction (RSOI), donor impurity and applied magnetic and electric fields. The exact diagonalization method has been used to solve the Hamiltonian of an electron confined in a quantum dot (QD) and obtain the eigenenergies and the binding energy of the donor impurity as a function of various QD physical parameters. We have shown the dependence of the average statistical energy, magnetization, magnetic susceptibility and heat capacity of the donor impurity in the QD on: the Rashba interaction parameter, the magnetic and electric fields, confining frequency, and temperature. The results reveal that these parameters can tune the magnetic properties of the GaAs quantum dot and flip the sign of magnetic susceptibility from negative (diamagnetic) to positive (paramagnetic) type material.

Role of Rashba spin-orbit interaction on polaron Zeeman effect in a two-dimensional quantum dot with parabolic confinement

We calculate the energies of the ground and the first excited states of a free polaron and that of a polaron bound to a Coulomb impurity in a quantum dot with harmonic confinement in the presence of Rashba spin-orbit interaction by employing the variation theory of Lee, Low and Pines as modified by Huybrechts for an all-coupling range of the electron-phonon interaction and arbitrary confinement length. We show that in both cases, the Rashba interaction removes the two-fold spin-degeneracy of the first-excited states even in the absence of any applied magnetic field, though the ground state does not show any such spin splitting. The self-energy corrections due to the polaronic effect are however not affected by the Rashba interaction. We also investigate the combined effect of Rashba and polaronic interactions in the presence of an external magnetic field using the Rayleigh-Schrödinger perturbation theory. Application of our results to GaAs and CdS quantum dots shows that the suppression of the phonon-induced size-dependent Zeeman splitting in a quantum dot is reduced by the Rashba coupling.

Spin Hall Conductance In a Two-Dimensional Tight-Binding Model In The Presence Of Rashba Spin-Orbit Interaction And Random Impurities

The spin-Hall conductance in a two-dimensional tight-binding model is studied in the presence of Rashba spin-orbit interaction and random impurities. The conventional definition of spin current falls through for a system with Rashba spin-orbit interaction because of the non-conservation of the spin magnetic moment in the presence of Rashba coupling. Using a modified definition of spin-current operator, the relaxation time for electron-impurity scattering is calculated with the help of Matsubara Green function and the spin-Hall conductivity is determined by employing the Kubo-Greenwood formalism. Our results show the explicit behavior of the spin-Hall conductance as a function of chemical potential, Rashba spin-orbit coupling constant and the impurity strength

Retro-normal reflection and specular Andreev reflection in a transition metal dichalcogenides superconducting heterojunction

Based on the Bogoliubov-de Gennes equation, the spin-resolved scattering problem through a transition metal dichalcogenides normal metal/superconductor has been investigated. It is shown that the tunneling conductances have a close relationship with the nontrivial Rashba metallic states. Without the Rashba spin–orbit interaction (RSOI), the tunneling conductances exhibit clear characteristic features for detecting the normal Rashba metal state (NRMS) and the anomalous Rashba metal state (ARMS). While in the presence of RSOI, the oscillation, hump structure, and the reentrant behavior of the tunneling conductances can be served as a smoking gun to distinguish the Rashba ring metal state (RRMS) from those nontrivial metallic states. Fundamentally, in sharp contrast to the NRMS and the ARMS where only the normal reflection and the retro-Andreev reflection can occur, the additional scattering processes of the retro-normal reflection (RNR) and the specular Andreev reflection (SAR) can take place in the present junction with the RRMS. Thus the obtained results offer a feasible way to determine the RNR, the SAR, and the nontrivial Rashba metallic states based on the transition metal dichalcogenides superconducting heterojunction.

Spin-orbit interaction and snake states in a graphene p-n junction

We study a model of a $p$-$n$ junction in single-layer graphene in the presence of a perpendicular magnetic field and spin-orbit interactions. By solving the relevant quantum-mechanical problem for a potential step, we determine the exact spectrum of spin-resolved dispersive Landau levels. Close to zero energy, we find a pair of linearly dispersing zero modes, which possess a wave-vector-dependent spin polarization and can be regarded as quantum analogous of spinful snake states. We show that the Rashba spin-orbit interaction, in particular, produces a wave vector shift between the dispersions of these modes with observable interference effects. These effects can in principle provide a way to detect the presence of Rashba spin-orbit interaction and measure its strength. Our results suggest that a graphene $p$-$n$ junction in the presence of strong spin-orbit interaction could be used as a building block in a spin field-effect transistor.

Electrically controllable spin transport in bilayer graphene with Rashba spin-orbit interaction

We study the spin transport in bilayer graphene nanoribbons (BGNs) in the presence of Rashba spin-orbit interaction (SOI) and external gate voltages. It is found that the spin polarization can be significantly enhanced by the interlayer asymmetry or longitudinal mirror asymmetry produced by external gate voltages. Rashba SOI alone in BGNs can only generate current with spin polarization along the in-plane y direction, but the polarization components can be found along the x, y and z directions when a gate voltage is applied. High spin polarization with flexible orientation is obtained in the proposed device. Our findings shed new light on the generation of highly spin-polarized current in BGNs without external magnetic fields, which could have useful applications in spintronics device design.

Optical properties of a few semiconducting heterostructures in the presence of Rashba spin-orbit interactions: a two-dimensional finite-difference numerical approach

In the present study, the effect of Rashba spin-orbit interactions on the electron energy states, spin-density distributions, and absorption coefficient of a few two-dimensional quantum dots with different confining potentials are studied. We use a finite-difference method to solve the resulting coupled Schrodinger equations. In our computations, since the concluded Hamiltonian matrix is found to be extensive; regardless of being blocked and sparse, implementing the Arnoldi factorization method for diagonalizing the Hamiltonian matrix is required. According to results, it is found that the interstate mixing that stemmed from the Rashba spin-orbit interaction can result in a new spin polarization. This occurrence explicitly justifies the observation of multiple peaks in the spin-density distributions. Furthermore, by increasing the quantum dot size, the absorption coefficient increases about 4 times. Finally, by increasing the Rashba parameter, the absorption peak decreases and a redshift takes place.

Persistent current in a chain of two Holstein-Hubbard rings in the presence of Rashba spin-orbit interaction

Persistent current in a chain of two Holstein-Hubbard rings in the presence of Rashba spin-orbit interaction

Unconventional charge and spin-dependent transport properties of a graphene nanoribbon with line-disorder

Electronic transport with a line (or a few lines) of Anderson-type disorder in a zigzag graphene nanoribbon is investigated in the presence of Rashba spin-orbit interaction. Such line-disorders give rise to a peculiar behavior in both charge as well as spin-polarized transmission in the following sense. In the weak-disorder regime, the charge transport data show Anderson localization up to a certain disorder strength, beyond which the extended states emerge and start dominating over the localized states. These results are the hallmark signature of a selectively disordered (as opposed to bulk disorder) graphene nanoribbon. However, the spin-polarized transport shows a completely contradicting behavior. Further, the structural symmetries are shown to have an important role in the spintronic properties of the nanoribbons. Moreover, the edge-disorder scenario (disorder selectively placed at the edges) seems to hold promise for the spin-filter and switching device applications.

Tunable magnetoresistance in spin-orbit coupled graphene junctions

Using the Landauer-B\"utikker formalism, we study the graphene magneto-transport in the presence of Rashba spin-orbit interaction (RSOI). We show that the angle resolved transmission probability in the proposed structures can be tuned by the RSOI strength. The transmission spectrum show Klein tunneling in the parallel (P) magnetization configuration which can be blocked by the RSOI. This effect is also observable for the anti-parallel (AP) magnetization configuration in different incident angle. The numerical results shows that the spin-polarized conductance strongly depends on the strength of the RSOI and can be generated by tuning the magnetic exchange field and RSOI strength. This spin-polarized conductance is a sensitive oscillatory function of the thickness of the RSO region. Because of the spin-flip effect, the junction shows a spin-valve effect with large and negative magnetoresistance (MR) and spin-magnetoresistance (SMR) in the presence of RSOI. When the RSOI is on, the frequency and amplitude of shot-noise and Fano factor's oscillations are also increased. These results can provide a way to extending the application of graphene-based junctions in spintronics.

Interface sensitivity on spin transport through a three-terminal graphene nanoribbon

Spin dependent transport in a three-terminal graphene nanoribbon (GNR) is investigated in presence of Rashba spin-orbit interaction. Such a three-terminal structure is shown to be highly effective in filtering electron spins from an unpolarized source simultaneously into two output leads and thus can be used as an efficient spin filter device compared to a two-terminal one. The study of sensitivity of the spin-polarized transmission on the location of the outgoing leads results in interesting consequences and is explored in details. There exist certain symmetry relations between the two outgoing leads with regard to spin-polarized transport, especially when they are connected to the system in a particular manner. We believe that the prototype presented here can be realized experimentally and hence the results can also be verified.

Spin-polarized currents in a two-terminal double quantum ring driven by magnetic fields and Rashba spin-orbit interaction

Aim of this study is to investigate spin transportation in double quantum ring (DQR). We developed an array of DQR to measure the transmission coefficient and analyze the spin transportation through this system in the presence of Rashba spin-orbit interaction (RSOI) and magnetic flux estimated using S-matrix method. In this article, we compute the spin transport and spin-current characteristics numerically as functions of electron energy, angles between the leads, coupling constant of the leads, RSOI, and magnetic flux. Our results suggest that, for typical values of the magnetic flux (ϕ/ϕ0) and Rashba constant (αR), such system can demonstrates many spintronic properties. It is possible to design a new geometry of DQR by incoming electrons polarization in a way to optimize the system to work as a spin-filtering and spin-inverting nano-device with very high efficiency. The results prove that the spin current will strongly modulate with an increase in the magnetic flux and Rashba constant.Moreover it is shown that, when the lead coupling is weak, the perfect spin-inverter does not occur.

The effects of Rashba spin-orbit coupling on spin-polarized transport in hexagonal graphene nano-rings and flakes

Quantum transport properties and spin polarization in hexagonal graphene nanostructures with zigzag edges and different sizes were investigated in the presence of Rashba spin-orbit interaction (RSOI). The nanostructure was considered as a channel to which two semi-infinite armchair graphene nanoribbons were coupled as input and output leads. Spin transmission and spin polarization in x, y, and z directions were calculated through applying Landauer-Buttiker formalism with tight binding model and the Green's function to the system. In these quantum structures it is shown that changing the size of system, induce and control the spin polarized currents. In short, these graphene systems are typical candidates for electrical spintronic devices as spin filtering.