Rashba Spin-orbit Interaction Strength 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.

Spin-dependent tunnelling time in phosphorene superlattice

ABSTRACT We study theoretically the Hartman effect and spin-dependent group delay time in a strained phosphorene superlattice in the presence of Rashba spin–orbit interaction (RSOI). It is found that the total group delay time depends on the spin degree of freedom. Thus, spin filtering can be obtained in the time domain by means of the phosphorene superlattice. The total group delay time can be efficiently controlled by the angles of incidence of electrons, strength of RSOI and number of superlattice barriers. Particularly, the magnitude of the total group delay time can be tuned via the direction and strength of strain. Therefore, in phosphorene superlattice the total group delay time can be efficiently adjusted mechanically. Moreover, in a strained phosphorene superlattice the superluminal tunnelling or Hartman effect can be observed even for a normal incident.

Spin polarization and heat generation matching in a quantum dot with magnetic background

Motivated by the increasing demand for designing spin-polarized quantum devices via electric manipulation, we theoretically studied the spin polarization induced by Rashba spin-orbit interaction (RSOI) and the heat generated by thermal bias in the normal metal(N)-(insulator(I), Quantum Dot(QD))-Superconductor(S) ring threaded by a magnetic flux. We observed that the effective dot level, ε¯d=0 or ε¯d=±ω02 (ω0: characteristic phonon frequency), is responsible for the outstanding spin polarization in different BCS gaps and that non-dissipative spin-polarized current is produced effectively by adjusting the RSOI strength and thermal bias. Furthermore, we concluded that the thermal bias accounts for the spin-polarized Andreev current through the s-wave superconducting electrode, rather than the electric bias. Overall, our work provides a novel method for producing non-dissipative pure spin current.

Spin splitting and spin polarization through a multi-terminal phosphorene quantum nanoring

In this paper, spin split, spin-polarization, and spin-flip effect were theoretically investigated through a three-terminal phosphorene quantum nanoring (PQNR) by using the Green’s function formalism in the presence of Rashba spin–orbit interaction (RSOI) and penetrating magnetic flux inside the ring. Our results show that the perfect spin splitting occurs because of the PQNR anisotropic structure. Furthermore, the spin polarization can be tunned by the RSOI strength and the energy of incident electrons. Consequently, this configuration can provide an efficient way to control the spin-dependent transport. Moreover, the structure can illustrate the full spin-flip effect that is irrespective of the injection source.

Lead position and lead-ring coupling effects on the spin-dependent transport properties in a two-dimensional network of quantum nanorings in the presence of Rashba spin–orbit interaction

The effects of lead positions and lead-ring coupling regimes are investigated for spin-related transport through a two-dimensional network of quantum nanorings (2DNQRs) considering Rashba spin–orbit interaction (RSOI) and magnetic flux. A matrix representation of the transmission and reflection coefficients through a single ring connected to the arbitrary number of leads has been introduced. As a specific example of 2DNQRs, the conductance, spin polarization and system efficiency are obtained via a triangular network of quantum rings (TNQRs). TNQRs are completely opaque or transparent versus RSOI strength and wave vector (k) of the incident electron. The periodicity of these functions along the k axis depends on the lead positions and is independent of lead-ring coupling. Also, the symmetric geometry and strong lead-ring coupling regime significantly improve the performance of the system as a multipurpose spintronic device (i.e., a perfect spin filter, spin splitter, spin switching, Stern–Gerlach device and an electronic switching device).

Giant magnetoresistance control and nontrivial metallic state manipulation in a transition-metal dichalcogenide spin-valve using a gate voltage

Here, we have theoretically studied the valley- and spin-resolved transport in a monolayer transition metal dichalcogenides based spin valve device, where both the Rashba spin orbit interaction and a gate voltage coexist in the central lead. In contrast to conventional semiconductor, nontrivial metallic states, such as, normal Rashba metal state (NRMS), anomalous Rashba metal state (ARMS), and Rashba ring metal state (RRMS), can be generated and manipulated by Rashba spin orbit interaction without the magnetic effect. For a nonferromagnetic double junction, it was found that the valley- and spin-resolved tunneling conductance can be effectively tuned by the incident energy, the junction length, the Rashba spin orbit interaction strength, and the gate voltage. Due to the spin texture and the Fermi wavevectors in the central lead, both the tunneling coefficient and the tunneling conductance all exhibit the remarkable characteristic features which enable us to diagnose the special states. For a ferromagnetic spin valve device, the resulting nontrivial metallic groundstates in the central lead also demonstrate directly in the giant magnetoresistance with notable unique features. We have further revealed that a perfect valley and spin giant magnetoresistance stems from the spin splitting and the spin-valley coupling. These valley- and spin-resolved phenomena are interesting for both fundamental research and 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.

Spin-dependent tunneling time and Hartman effect in silicene

We theoretically investigate the tunneling time, including group delay and dwell time, through silicene barrier in the presence of extrinsic Rashba spin-orbit interaction (RSOI). It is found that the group delay and dwell time depend on the spin state of electron and have an oscillatory behavior with respect to on-site potential difference between A and B sublattices (Δz) and barrier width. Furthermore similar to graphene the group delay time for normal incident angle is independent of spin state of electron, while unlike the graphene, the superluminal tunneling or Hartman effect can be observed even at the normal incidence. Moreover, the difference of the dwell time between spin-up and spin-down can be efficiently tuned by the (Δz) and extrinsic RSOI strength.

Extrinsic Rashba spin-orbit interaction effect on shot noise properties in silicene superlattice

We theoretically study the spin-dependent transmission and shot noise properties in silicene superlattice with extrinsic Rashba spin–orbit interaction (RSOI). It is found that the new Dirac-like point is determined by the ratio of well width to barrier width. The Fano factor shows a peak at new Dirac-like point. Also, Fano factor has an oscillatory behavior for the both spin-up and spin-down electrons with respect to extrinsic RSOI strength and the oscillation period decreases by increasing the number of barriers. The results indicate that the shot noise of a spin state can be efficiently controlled by the on-site potential difference between A and B sublattices (Δz), which can be tuned by the local electric field. The Fano factor increases by increasing the Δz and plateau of the Fano factor is formed. In this case, the transmission can be blocked by the electric barrier and the Fano factor approaches 1.

Spin flip in single quantum ring with Rashba spin–orbit interation**Project supported by the National Natural Science Foundation of China (Grant No. 11504016).

We theoretically investigate spin transport in the elliptical ring and the circular ring with Rashba spin–orbit interaction. It is shown that when Rashba spin–orbit interaction is relatively weak, a single circular ring can not realize spin flip, however an elliptical ring may work as a spin-inverter at this time, and the influence of the defect of the geometry is not obvious. Howerver if a giant Rashba spin–orbit interaction strength has been obtained, a circular ring can work as a spin-inverter with a high stability.

Electromagnetically induced transparency in a quantum pseudo-dot with spin–orbit interaction

Electromagnetically induced transparency of a quantum pseudo-dot with Rashba spin–orbit interaction and under the influence of external magnetic field is investigated. To study electromagnetically induced transparency the dependence of absorption coefficient and refractive index of the probe light pulse on the Rashba spin–orbit interaction strength, magnetic field, dot size and parameters of pseudo-harmonic potential is explained. Results show the considerable effects of SOI and other mentioned parameters on the electromagnetically induced transparency of the system.

Weak antilocalization induced by Rashba spin-orbit interaction in layered III-VI compound semiconductor GaSe thin films

Magnetoconductance (MC) at low temperature was measured to investigate spin-related transport affected by spin-orbit interaction (SOI) in III-VI compound $n$-type GaSe thin films. Results reveal that MC shows weak antilocalization (WAL). Its temperature and gate voltage dependences reveal that the dominant spin relaxation is governed by the D'yakonov-Perel' mechanism associated with the Rashba SOI. The estimated Rashba SOI strength in GaSe is much stronger than that of III-V compound GaAs quantum wells, although the energy gap and spin split-off band in GaSe closely resemble those in GaAs. The angle dependence of WAL amplitude in the in-plane magnetic field direction is almost isotropic. This isotropy indicates that the strength of the Dresselhaus SOI is negligible compared with the Rashba SOI strength. The SOI effect in $n$-GaSe thin films differs greatly from those of III-V compound semiconductors and transition-metal dichalcogenides.

Tunability of Andreev levels via spin-orbit coupling in Zeeman-split Josephson junctions

We study Andreev reflection and Andreev levels $\ensuremath{\varepsilon}$ in Zeeman-split superconductor/Rashba wire/Zeeman split superconductor junctions by solving the Bogoliubov--de Gennes equation. We theoretically demonstrate that the Andreev levels $\ensuremath{\varepsilon}$ can be controlled by tuning either the strength of Rashba spin-orbit interaction or the relative direction of the Rashba spin-orbit interaction and the Zeeman field. In particular, it is found that the magnitude of the band splitting is tunable by the strength of the Rashba spin-orbit interaction and the length of the wire, which can be interpreted by a spin precession in the Rashba wire. We also find that if the Zeeman field in the superconductor has the component parallel to the direction of the junction, the $\ensuremath{\varepsilon}\ensuremath{-}\ensuremath{\phi}$ curve becomes asymmetric with respect to the superconducting phase difference $\ensuremath{\phi}$. Whereas the Andreev reflection processes associated with each pseudospin band are sensitive to the relative orientation of the spin-orbit field and the exchange field, the total electric conductance interestingly remains invariant.

Spin-dependent transport properties in strained silicene with extrinsic Rashba spin–orbit interaction

We theoretically investigate the spin-dependent transport properties in a silicene junction, with extrinsic Rashba spin–orbit interaction (RSOI), in the presence of strain. Due to the RSOI coupling, spin-inversion can be achieved. The spin resolved conductance and spin- inversion effect can be efficiently tuned by RSOI and strain strength. In addition, for particular values of RSOI strength, electrons with perfect spin-inversion transmit through the junction. It is found that for the armchair direction strain, unlike the zigzag direction the spin polarization can be observed and it increases with increasing the RSOI strength. The magnitude and sign of spin polarization can be manipulated by strain. The spin polarization reaches a maximum value at 2% strain.

Spin-dependent conductance and shot noise in graphene based periodic velocity barrier

We theoretically investigate the spin-dependent conductance and shot noise properties in graphene based periodic velocity barrier structure under Rashba spin–orbit interaction (RSOI). The system consists of graphene sheet in which the Fermi velocity and the electrostatic potential vary in space. We find that the spin-dependent conductance and shot noise in graphene can be efficiently controlled by tuning the Fermi velocity. Moreover, changing the Fermi velocity allows us to change the positions of the Dirac points. The spin-dependent Fano factor without and with spin flip increases and decreases, respectively with increasing the RSOI strength. When Fermi velocity in the barriers is smaller than the velocity outside the barriers, we find that the Fano factor for outgoing electrons with opposite spins has an oscillatory behavior with respect to the RSOI strength. Specifically, as the number of velocity barriers increases or Fermi velocity decreases the spin polarization increases.

Optical properties of wedge-shaped quantum dots under Rashba spin–orbit interaction

In the present paper, the optical properties of a GaAs wedge-shaped quantum dot (QD) under the effect of Rashba spin–orbit interaction (SOI) are theoretically studied. For this purpose, we have used analytical expressions for optical properties obtained by the compact-density matrix formalism. The dependence of the optical absorption coefficients and refractive index changes on the strength of Rashba SOI for different angles and different radii of wedge-shaped QD has been studied. According to the obtained results, it is found that (i) the Rashba SOI does not have considerable effects on the refractive index changes maxima. (ii) The total absorption coefficient is increased and shifted towards higher energies with considering the Rashba SOI. (iii) The influence of Rashba SOI on the optical properties depends on the parameters such as apex angle and radius of the wedge-shaped QD.

Rashba and Dresselhaus spin-orbit interactions effects on electronic features of a two dimensional elliptic quantum dot

In this paper, electronic structure of a two dimensional elliptic quantum dot under the influence of external electric and magnetic fields are studied in the presence of Rashba and Dresselhaus spin-orbit interactions. This investigation is done computationally and to do this, at first, the effective Hamiltonian of the system by considering the spin-orbit coupling is demonstrated in the presence of applied electric and magnetic fields and afterwards the Schrödinger equation is solved using the finite difference approach. Utilizing finite element method, eigenvalues and eigenstates of the system are calculated and the effect of the external fields, the size of the dot as well as the strength of Rashba spin-orbit interaction are studied. Our results indicate that, Spin-orbit interactions, external fields and the dot size have a great influence on the electronic structure of the system.

Rashba Spin Orbit Interaction Effect on Spin Current in a Quantum Wire with Magnetic Field

We study the spin current in a quantum wire subjected to magnetic fields in the presence of Rashba spin orbit interaction. For an infinite superlattice wire, we find that the spin current density is strongly affected by the nature of the sub bands. The results are presented as a function of transverse coordinate, magnetic field and Rashba spin orbit interaction strength. Our results indicate an increase of spin current density with the increase of Rashba factor. The roles of confinement strength and magnetic fields as control parameters on the spin current have been demonstrated.

Radius effect on the spintronic properties of a triangular network of quantum nanorings in the presence of Rashba spin-orbit interaction

The effect of radius on conductance and spin transport through a triangular array of quantum nanorings (QR) in the presence of Rashba spin-orbit interaction (RSOI) is studied. By using wave-guide theory, we obtain the conductance through such network as a function of RSOI strength and the wave vector k of the incoming electrons, with rings of equal and different radius. It is shown that in the network with rings of different radius and local modulations of RSOI, the input current can be directed to any of output ports, so it can be used as a switching device. In addition, in the certain ranges of k, the network can be perfectly opaque, depending on the value of RSOI strength and ring radius. Besides, considerable pure spin currents can be revealed in the two output leads with the same amplitude and reverse polarizations.

Spin polarized bound states in the continuum in open Aharonov–Bohm rings with the Rashba spin–orbit interaction

We consider the trapping of electrons with a definite spin polarization by bound states in the continuum (BSC) in the open Aharonov–Bohm rings in the presence of the Rashba spin–orbit interaction (RSOI). Neglecting the Zeeman term we show the existence of BSCs in the one-dimensional ring when the eigenstates of the closed ring are doubly degenerate. With account of the Zeeman term BSCs occur only at the points of threefold degeneracy. The BSCs are found in the parametric space of flux and RSOI strength in close pairs with opposite spin polarization. Thereby the spin polarization of electrons transmitted through the ring can be altered by minor variation of magnetic or electric field at the vicinity of these pairs. Numerical simulations of the two-dimensional open ring show similar results for the BSCs. Encircling the BSC points in the parametric space of the flux and the RSOI constant gives rise to a geometric phase.