Weak Rashba Spin-orbit Coupling Research Articles

Spin and spin-valley filter analysis of inner-edge states in hybrid silicene-like nanoribbons

The band structure and the topological property of the silicene-like nanoribbon (SiNR) can be regulated by external fields. The hybrization of SiNRs regulated by external fields may generate some special spin/valley properties of the inner-edge states. In this paper, we introduce three external fields: staggered electric field, antiferromagnetic exchange field and Haldane light field in SiNR systems. We analyze the hybridizations of the two and three SiNRs with two adjacent nanoribbons in different topological states, which generate the inner-edge states with some spin and valley properties. These hybrid systems may be used as the spin filter and spin-valley filter. We give the systematical and detailed investigations on these inner-edge-state spin and spin-valley filter properties for these hybrid SiNR systems. Especially for the hybrid three-ribbon systems, we consider the case only with the inner-edge states. Furthermore, we observe that the inner-edge state is robust against the weak Rashba spin–orbit coupling, the moderate disorder and the outer imperfections. In addition, the inner-edge state is absolutely broken as the vacancy is in the inner edge. We believe these inner-edge-state spin/valley filters have very wide applications in the future spintronic and valleytronic devices.

P -wave superconductivity in weakly repulsive 2D Hubbard model with Zeeman splitting and weak Rashba spin-orbit coupling

We study the superconducting order in a two-dimensional square lattice Hubbard model with weak repulsive interactions, subject to a Zeeman field and weak Rashba spin-orbit interactions. Diagonalizing the non-interacting Hamiltonian leads to two separate bands, and by deriving an effective low-energy interaction we find the mean field gap equations for the superconducting order parameter on the bands. Solving the gap equations just below the critical temperature, we find that superconductivity is caused by Kohn-Luttinger type interaction, while the pairing symmetry of the bands are indirectly affected by the spin-orbit coupling. The dominating attractive momentum channel of the Kohn-Luttinger term depends on the filling fraction $n$ of the system, and it is therefore possible to change the momentum dependence of the order parameter by tuning $n$. Moreover, $n$ also determines which band has the highest critical temperature. Rotating the magnetic field changes the momentum dependence from states that for small momenta reduce to a chiral $p_x \pm i p_y$ type state for out-of-plane fields, to a nodal p-wave type state for purely in-plane fields.

Electron spin resonance and Rashba field in GaN-based materials

We discuss problem of Rashba field in bulk GaN and in GaN/AlxGa1−xN two-dimensional electron gas, basing on results of X-band microwave resonance experiments. We point at large difference in spin–orbit coupling between bulk material and heterostructures. We observe coupled plasmon–cyclotron resonance from the two-dimensional electron gas, but no spin resonance, being consistent with large zero-field spin splitting due to the Rashba field reported in the literature. In contrast, small anisotropy of g-factor of GaN effective mass donors indicates rather weak Rashba spin–orbit coupling in bulk material, not exceed 400G, αBIA<4×10−13eVcm. Furthermore, we observe new kind of electron spin resonance in GaN, which we attribute to surface electron accumulation layer. We conclude that the sizable Rashba field in GaN/AlxGa1−xN heterostructures originates from properties of the interface.

Band structures of carbon nanotube with spin–orbit coupling interaction

We explore the band structures of single-walled carbon nanotubes (SWCNTs) with two types of spin–orbit couplings. The obtained results indicate that weak Rashba spin–orbit coupling interaction can lead to the breaking of four-fold degeneracy in all tubes even though without the intrinsic SO coupling. The asymmetric splitting between conduction bands and valence bands is caused by both SO couplings at the same time. When the ratio of Rashba spin–orbit coupling to the intrinsic spin–orbit coupling is larger than 3, metallic zigzag nanotube is always metallic conductor, on the contrary it becomes semiconducting properties. However, only when this ratio is equal to about 3 or the intrinsic spin–orbit coupling is much weak, the metallic armchair nanotube still holds the metallic behavior in transport.

SPIN CURRENT INDUCED ELECTRIC FIELD IN A RASHBA QUANTUM WIRE

We investigate theoretically the spin current and spin current induced electric field in a weak Rashba spin-orbit coupling quantum wire (QW) using a definition for spin current by means of scattering matrix. It is found that there exists two non-zero linear spin current density elements which have oscillation peaks at the center of QW and their strengths can be changed by the number of propagation modes and Rashba constant, respectively. Moreover, the spin current induced electric field has also been calculated and its strength is measurable with present technology with which can be used to detect spin current.

A possible realization of spin filter using a quantum wire with Rashba spin-orbit coupling

We study theoretically the spin-polarized electron transport properties for a weak Rashba spin-orbit coupling (SOC) quantum wire connected nonadiabatically to two normal-conductor electrode leads. The influence of both the mode mixing due to wire-lead connection and Rashba SOC split on the spin-polarized electron transport is treated simultaneously by means of scattering matrix within the framework of effective free-electron approximation. The analytical analysis with numerical examples demonstrates that the purely spin-polarized current can occur for the system with an appropriate system geometry and material parameters. Our result may imply a simple approach to the design of a spin filter device without containing any magnetic materials or applying a magnetic field.

Persistent Spin Current in a Quantum Wire with Weak RashbaSpin–Orbit Coupling

We theoretically investigate the spin current for a parabolicallyconfined semiconductor heterojunction quantum wire with weak Rashbaspin–orbit coupling by means of the perturbation method. By analyticalcalculation, it is found that only two components of spin currentdensity is non-zero in the equilibrium case. Numerical examples havedemonstrated that the spin current of electron transverse motion is10−3 times that of electron longitudinal motion. However, theformer one is much more sensitive to the strength of Rashba spin–orbitcoupling. These results may suggest an approach to the spin storagedevice and to the measurement of spin current through its inducedelectric field.

Conductance for a Quantum Wire with Weak Rashba Spin-OrbitCoupling

We theoretically study the low temperature electron transport propertiesof a weak Rashba spin-orbit coupling (SOC) semiconductor quantum wireconnected nonadiabatically to two electrode leads without SOC. The wireand the leads are defined by a parabolic confining potential, and theinfluence of both the wire-lead connection and the Rashba SOC on theelectron transport is treated analytically by means of scattering matrixwithin effective free-electron approximation. From analytical analysisand numerical examples, we find that the system shows some fractionalquantum conductance behaviour, and for some particular wire width a purespin polarized current exists. Our result may imply a simple method forthe design of a spin filter without involving any magnetic materials ormagnetic fields.

CURRENT INDUCED LOCAL SPIN POLARIZATION DUE TO THE SPIN-ORBIT COUPLING IN A TWO DIMENSIONAL NARROW STRIP

The current induced local spin polarization due to weak Rashba spin-orbit coupling in narrow strip is studied. In the presence of longitudinal charge current, local spin polarizations appear in the sample. The spin polarization perpendicular to the plane has opposite sign near the two edges. The in-plane spin polarization in the direction perpendicular to the sample edges also appears, but does not change sign across the sample. From our scaling analysis based on increasing the strip width, the out-of-plane spin polarization is important mainly in a system of mesoscopic size, and thus appears not to be associated with the spin-Hall effect in bulk samples.

Rashba splitting in Kane type quantum disk

Electrons in Kane type semiconductor quantum disk in presence of Rashba spin–orbital interaction and external magnetic field parallel to axis of quantum disk are considered theoretically. A three-level model of the kp theory is used to describe electrons in weak Rashba spin–orbit coupling regimes and external magnetic field, taking into account the main features of the band structure in InSb-type semiconductors: a small energy gap, a strong spin–orbit interaction. We calculated the radii, thickness, coupling strength, and magnetic field dependence of Rashba splitting for electrons. It has been seen that the Rashba splitting of the electrons are decreased with the increasing of radius.

Rashba spin splitting in semiconductor quantum wires

A general three-dimensional model for asymmetric semiconductor quantum wires is introduced with exact and analytical solutions for the spin-dependent electronic structure. Simple expressions are obtained for the eigenvalues, wave functions, and spin expectation values, valid in both strong and weak Rashba spin-orbit coupling regimes. For III-V quantum wires, the Rashba interaction is shown to be typically in the weak coupling regime and to lead to considerable spin mixing only near the anticrossings, seen only in narrow-gap quantum wires. For realistic wires, the Rashba splitting is shown to decrease with increasing wire confinement.