Effect Of Rashba Spin-orbit Interaction Research Articles

Combined effect of rashba spin-orbit interaction, hydrostatic pressure and temperature on energy dispersion based ballistic conductance of InAs tunnel-coupled (double) quantum wire under exterior magnetic and electric field

In this work the change in energy dispersion curve and ballistic conductance for InAs tunnel-coupled double quantum wire (DQWR) under the influence of the external magnetic field, electric field, hydrostatic pressure, temperature, and Rashba spin-orbit interaction (SOI) are studied theoretically in detail. A constant magnetic field transverse to the fundamental plane is applied to the DQWR. The Landuer-Büttiker formalism is used to determine the transport characteristics, and the energy eigenvectors and eigenvalues are derived within the parameters of the diagonalization approach. The numerical results indicate that the energy spectra of the system are influenced by external factors such as magnetic field, electric field, temperature, hydrostatic pressure, and Rashba SOI, resulting in variations in lateral/vertical and downward/upward shifts. These factors also cause oscillatory patterns in ballistic conductance due to the oddity of energy subbands. These results have significant implications for the advancement of double-quantum wire-based devices.

Rashba effect on linear and nonlinear optical properties of a cylindrical core/shell heterojunction quantum dot

Rashba effect may play an important role in the nonlinear optical properties of heterojunction quantum dots. In this work, we have theoretically examined the effects of Rashba spin-orbit interaction on an electron in a cylindrical core/shell quantum dot (CCSQD). The modifications of various properties of cylindrical core/shell quantum dot such as transition energies, dipole transition matrix elements and linear and nonlinear optical properties due to change in Rashba coupling parameter, magnetic field and effective Rydberg energy were studied. We solved the Schrödinger equation using numerical methods and obtained energy eigenvalues as functions of the aforementioned parameters. It was observed that, the magnetic field has a considerable effect on absorption coefficients and refractive index. It was also observed that increasing the magnetic field shifts the resonances towards higher energies. Additionally, increasing in the Rashba coupling coefficient (αR) was found out to result an increase in absorption coefficients and refractive index. Our results demonstrated that, we can manipulate optical properties of cylindrical core/shell quantum dot using an external magnetic field.

Modeling for Improved Performance of Ultra-Fast Nonvolatile Toggle Spin Torque MRAM Bit-Cell

In the recent past, exploiting nonvolatile memory devices to facilitate in-memory computation benchmarks has demonstrated a considerable capability to address the von-Neumann drawbacks. This process resulted in a tremendous effort towards spintronics memory development. Due to the voltage-controlled magnetic anisotropy (VCMA) effect, the toggle magnetoresistive random-access memory (MRAM) exhibits faster switching and lower power consumption than spin-transfer torque (STT) MRAM. We assessed read/write access time, magnetized time and anisotropic field for crystalline perpendicular magnetic tunnel junctions (CPMTJ) with detailed material study and device parameters in this work. These junctions are affected by the VCMA effect. Various VCMA parameters, including the VCMA coefficient, the time constant and antiparallel (AP) resistance on the saturated magnetization, are measured via the memory cell’s SPICE modeling. The Rashba spin–orbit interaction (SOI) and spin-valve model are developed by MATLAB scripting for evaluating a Rashba and Hamiltonian vector field. The toggle spin torque (TST) in the TST-MRAM cell is generated due to the interconnection between STT and spin–orbit torque (SOT) mechanisms. The TST-MRAM cell’s benefits are energy efficiency, large TMR ratio and superfast read and write operation. This work’s novel part is that the Hamiltonian field can control the net magnetization factor by the Rashba SOI effect. We end this paper with the performance enhancement techniques of MRAM cells due to VCMA and Rashba SOI effect.

Superarrival and spin polarization of spin-dependent wave-packets propagating through one-dimensional rectangular and inverse parabolic barriers: Rashba spin-orbit interaction and nonlinearity effects

In this paper, we study the effects of Rashba spin-orbit interaction, quantum barrier shape, barrier height, etc. on the spin polarization and less studied superarrival of spin-dependent Gaussian wave-packets propagating through one-dimensional rectangular and inverse parabolic quantum barriers. We show that in some situations the transient inverse parabolic barrier can be regarded as a reflectionless dispersion reducing tool for wave-packet propagation applications. Spin up and down components of the wave-packet have different Superarrivals and they can be tuned by means of the strength of the Rashba parameter. The superarrival effect is also very sensitive to the strength of the nonlinearity and can be eliminated by using a small 0.3 nonlinearity strength. Superarrival depends just on the physical properties of the system and the spin polarization of the incident initial wave packet does not affect it.

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.

Spin torque induced spin current in a two-dimensional tight-binding system with Rashba coupling in the presence of random impurities

The effect of Rashba spin-orbit interaction on quantum transport in a two-dimensional tight-binding system is studied in the presence of random impurities. The relaxation time for the impurity scattering is calculated using the Matsubara Green function technique and the spin and charge conductivities are determined using the Kubo formalism. The relaxation time, charge and spin conductivities are shown to exhibit peak structures at a critical chemical potential, the peak of the spin conductivity being higher than that of charge conductivity. It is also shown that the Rashba interaction increases the peaks of the charge and spin conductivities, while the impurity coupling decreases them. In case of relaxation time, however, the peak value remains unaffected by RSOI. It is furthermore shown that in general, the relaxation time, and charge and spin conductivities are enhanced by RSOI while they are reduced by impurities.

NAND/AND/NOT logic gates response in series of mesoscopic quantum rings

There is a special class of logic gates, called universal gates, any one of which is sufficient to express any desired computation. The NAND gate is truly global, given that it is already known, each Boolean function can be represented in a circuit that contains only NOT and AND gates, it is sufficient to show that these gates can be defined from the NAND gate. The effect of Rashba spin-orbit interaction (SOI) on the gate response and spin current density in a series of non-interacting one-dimensional rings connected to some leads is studied theoretically within the waveguide theory. The gates response and spin current density are computed in geometry of the system containing two terminal double quantum rings. Also, the presence and absence of Rashba SOI are treated as the two inputs of the AND/NAND/NOT gates. Furthermore, simulation of the device performance demonstrates that vital improvement toward spintronic applications can be achieved by optimizing device parameters such as magnetic flux and Rashba coefficient.

Rashba splitting of Dirac points and symmetry breaking in strained artificial graphene

The effect of Rashba spin-orbit interaction and anisotropic strain on the electronic, optical and thermodynamic properties of artificial graphene-like superlattice composed of InAs-GaAs quantum dots has been considered theoretically. The electronic energy dispersions have been obtained using Green's function formalism in combination with Fourier transformation to the reciprocal space and an exact diagonalization technique. We have observed a splitting of Dirac points and appearance of edditional Dirac-like points due to the Rashba spin-orbit interaction. Breaking of the hexagonal symmetry of the dispersion surfaces caused by the strain anisotropy is observed as well. It is shown that both the spin-orbit interaction and strain anisotropy have a qualitative impact on the measurable characteristics of the considered structure and can be used as effective tools to control the performance of devices based on artificial graphene.

The effect of Rashba spin-orbit interaction on persistent current in a chain of two Holstein-Hubbard rings

We study the persistent current in a chain of two coupled quantum rings threaded by an Aharonov-Bohm flux in the presence of electron-phonon and Rashba spin-orbit interactions. In the framework of the Holstein-Hubbard model, the equations for ground state energy, persistent current and Drude weight were derived. Obtaining of the expression for the ground state energy allowed us to obtain the persistent current by a conventional way (differentiating). The influence of the magnetic flux and the Rashba spin-orbit interaction on the ground state energy, persistent current and Drude weight was studied numerically.

Influences of temperature and Rashba spin-orbit interaction on oscillation period of bound polaron in quantum pseudodot

In the present work, we study the influences of the temperature and the Rashba spin-orbit interaction on the oscillation period of the bound polaron in the quantum pseudodot using the Lee-Low-Pines unitary transformation, the variational method of Pekar-type and the quantum statistical theory. We have derived the oscillation period of the bound polaron in the superposition state and reported the temperature dependences and the Rashba spin-orbit interaction effects of the oscillation period of polaron when the wave vector, the electron-LO phonon coupling, the Coulomb bound potential and the chemical potential take different values.

The effect of Rashba spin-orbit interaction on electronic and optical properties of a double ring-shaped quantum dot

In this work, we analytically study the effects of the Rashba spin-orbit interaction (SOI) and magnetic field on energy levels and optical properties of a double ring-shaped quantum dot. For this purpose, we first solve the Schrödinger equation and obtain the energy eigenvalues and the wave functions. Then, we use analytical expressions for optical properties obtained by the compact-density matrix formalism. We calculate the total refractive index change and total absorption in the presence of applied magnetic field and Rashba SOI. It is found that the energy levels strongly depend on the combined effects of the Rashba SOI and the applied magnetic field. The energy levels split into two branches, spin-up and spin-down states, due to the Rashba spin-obit interaction. The peak positions of both optical properties shift towards higher energies with increasing the magnetic field and Rashba parameter.

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.

Aharonov-Bohm effect in a helical ring with long-range hopping: Effects of Rashba spin-orbit interaction and disorder

We study Aharonov-Bohm effect in a two-terminal helical ring with long-range hopping in presence of Rashba spin-orbit interaction. We explore how the spin polarization behavior changes depending on the applied magnetic flux and the incoming electron energy. The most interesting feature that we articulate in this system is that zero-energy crossings appear in the energy spectra at $\Phi=0$ and also at integer multiples of half-flux quantum values ($n \Phi_0/2$, $n$ being an integer) of the applied magnetic flux. We investigate the transport properties of the ring using Green's function formalism and find that the zero energy transmission peaks corresponding to those zero energy crossings vanish in presence of Rashba spin-orbit interaction. We also incorporate static random disorder in our system and show that the zero energy crossings and transmission peaks are not immune to disorder even in absence of Rashba spin-orbit interaction. The latter prevents the possibility of behaving these helical states in the ring like topological insulator edge states.

20pAU-6 ディラック電子系の磁場応答に対するラシュバ型スピン軌道相互作用の効果

20pAU-6 ディラック電子系の磁場応答に対するラシュバ型スピン軌道相互作用の効果

Rashba spin-orbit coupling effects on the optical properties of double quantum wire under magnetic field

We investigate the effects of Rashba spin-orbit interaction on the optical absorption coefficients and refractive index changes associated with transitions between the first two lower-lying electronic levels in double quantum wire. The wire system represented by a symmetric, double quartic-well confinement potential is subjected to a perpendicular magnetic field. The analytical expressions of the linear and third-order nonlinear optical absorption coefficients and refractive index changes are obtained by using the compact-density matrix formalism and iterative scheme. Optical properties are investigated as a function of structural parameter, magnetic field, Rashba spin-orbit interaction and photon energies. Numerical results reveal that competing effects between spin-orbit interaction and magnetic field modify strongly the optical properties and can be altered by these parameters.

Spin accumulation in the parallel-coupled double quantum dots with Rashba spin-orbit interaction connected with ferromagnetic and superconducting electrodes

Using the standard nonequilibrium Green’s function techniques, we investigate the effect of Rashba spin-orbit interaction (RSOI) and ferromagnetic electrode on the spin accumulation in the parallel-coupled double quantum dots coupled with a ferromagnetic and a superconducting electrode. It is demonstrated that FM electrode cannot induce the spin polarization of Andreev reflection (AR) current, but can induce the spin accumulation in the QDs. However, RSOI can lead to the spin polarization of AR current as well as the spin accumulation in the QDs. In the existence of RSOI, complete spin-polarized QD can be achieved with negative bias voltage [Formula: see text], which is the most significant advantage of our device. When energy levels [Formula: see text] and the interdot coupling strength [Formula: see text], the maximum value of spin accumulation in this paper is obtained as 0.7. The results may be useful on the design of spintronic devices.

Electron transport through a two-terminal Aharonov-Bohm interferometer coupled with linear di-quantum dot molecules

A two-terminal Aharonov-Bohm (A-B) interferometer coupled with linear di-quantum dot molecules is presented. By employing Keldysh non-equilibrium Green's function technique, the conductance without introducing time-dependent external field and the average current with applying time-dependent external field are theoretically studied. In the absence of time-dependent external field, two identical linear diquantum dot molecules embedded respectively in the two arms of A-B interferometer lead to degeneracy energy levels. The central resonance peak at εd = 0 in the conductance spectrum splits into two resonance peaks as the inter-coupling strength of di-quamtum dot increases over a threshold. In the case that the two linear di-quantum dot molecules are different, three or four resonance peaks appear in the conductance spectrum. When tuning magnetic flux ψ= π, the destructive quantum interference of electron waves in the A-B interferometer takes place. The conversion between 0 and 1 for conductance is performed by switching on/off the magnetic flux, which suggests a new physical scheme of quantum switches. The effect of Rashba spin-orbit interaction on the conductance is discussed. The functionality of spin filter is suggested through adjusting the Rashba spin-orbit coupling strength and the external magnetic flux. When time-dependent external field is applied, the notable side-band effect appears in the average current curve. A series of resonance peaks is produced, with the peak-peak separation of ħω. Two main peaks become reduced as the amplitude of time-dependent external field increases, however, the sideband peaks grow gradually. This indicates that both the magnitude and the position of average current resonance peak are controllable by adjusting the amplitude of time-dependent external field. The sideband effect remains always in the average current curve no matter how much the frequency of time-dependent external field changes. But the increase in the frequency of external field leads to the growth of two main peaks at the bonding and anti-bonding energy respectively, and the decay of the corresponding sideband peaks as well. The conversion between the current peak and valley can be realized by tuning the frequency of time-dependent field. Moreover, the dependence of A-B effect of the average current on the magnetic flux is found. As the magnetic flux is ψ≠nπ, each peak in average current curves splits into two peaks. But under the condition of ψ=2nπ, the splitting phenomenon disappears. The spin-dependent average current shows effective controllability by tuning the magnetic flux and Rashba spin-orbit coupling. The results would be useful for gaining a physical insight into electron transport in the multi-quantum-dot molecules coupled A-B interferometer and for designing the quantum devices.

Spin–orbit effects on the nonlinear optical properties of a quantum dot in simultaneous electric and magnetic fields

We report on the nonlinear optical properties of a quantum dot including the Rashba spin–orbit interaction (RSOI) with external electric and magnetic fields. The effect of dot size is considered. We do not make any assumptions about the strength of the confinement. We use the numerical diagonalization of the Hamiltonian to determine the electronic structure. The confining potential is taken to be of the Woods–Saxon type. We find the effect of RSOI on nonlinear optical coefficients.

Signatures of Rashba spin-orbit interaction in charge and spin properties of quantum Hall systems

We study the local equilibrium properties of two-dimensional electron gases at high magnetic fields in the presence of random smooth electrostatic disorder, Rashba spin-orbit coupling, and the Zeeman interaction. Using a systematic magnetic length (${l}_{B}$) expansion within a Green's function framework we derive quantum functionals for the local spin-resolved particle and current densities which can be useful for future studies combining disorder and mean-field electron-electron interaction in the quantum Hall regime. We point out that the spin polarization presents a peculiar spatial dependence which can be used to determine the strength of the Rashba coupling by local probes. The spatial structure of the current density, consisting of both compressible and incompressible contributions, also essentially reflects the effects of Rashba spin-orbit interaction on the energy spectrum. We show that in the semiclassical limit ${l}_{B}\ensuremath{\rightarrow}0$ the local Hall conductivity remains, however, still quantized in units of ${e}^{2}/h$ for any finite strength of the spin-orbit interaction. In contrast, it becomes half-integer quantized when the latter is infinite, a situation which corresponds to a disordered topological insulator surface consisting of a single Dirac cone. Finally, we argue how to define at high magnetic fields a spin Hall conductivity related to a dissipationless angular momentum flow, which is characterized by a sequence of plateaus as a function of the inverse magnetic field (thus free of resonances).

Study of the properties of strong-coupling magnetopolaron in quantum disks induced by the Rashba spin-orbit interaction

On the basis of Lee-Low-Pines unitary transformation, the properties of strong-coupling magnetopolarons in quantum disks (QDs) induced by the Rashba spin-orbit interaction are studied using the Tokuda improved linearly combined operator method. Results show that the state properties of magnetopolarons are closely linked with the sign of the interaction energy Eint, and the Eint of magnetopolarons changes with the transverse confinement strength 0, the cyclotron frequency of the external magnetic field c, the electron-LO phonon coupling strength , and the thickness L of QDs. The average number N of phonons increases with increasing c, 0 and , but the oscillation decreases with increasing thickness L of QDs. The effective mass m0* of magnetopolarons splits into two (m+*, m-*), induced by the Rashba spin-orbit interaction, and the values of them increase with increasing c, 0 and , but the oscillation decreases with increasing thickness L of QDs. For the ground state of magnetopolarons in QDs, the electron-LO phonon interaction plays a significant role, meanwhile, the Rashba spin-orbit coupling effect cannot be ignored. Only for the lower volocity of the electrons, can the polaron effect and the Rashba spin-orbit interaction effect on the magnetopolaron be obvious.