Rashba spin-orbit interaction in graphene armchair nanoribbons

We study graphene nanoribbons (GNRs) with armchair edges in the presence of Rashba spin- orbit interactions (RSOI). We impose the boundary conditions on the tight binding Hamiltonians for bulk graphene with RSOI by means of a sine transform and study the influence of RSOI on the spectra and the spin polarization in detail. We derive the low energy approximation of the RSOI Hamiltonian for the zeroth and first order in momentum and test their ranges of validity. The choice of a basis appropriate for armchair boundaries is important in the case of mode-coupling effects and leads to results that are easy to work with.     

Transport in magnetic graphene superlattice with Rashba spin-orbit interaction

Based on the transfer-matrix method, we have investigated the spin-dependent transport properties of magnetic graphene superlattice in the presence of Rashba spin-orbit interaction (RSOI). It is shown that the angular range of the spin transmission probability through magnetic graphene superlattice can be efficiently controlled by the number of barriers. As the number of magnetic barriers increases, the angular range of the transmission through the magnetic superlattice decreases, the gaps in the transmission and conductivity versus energy become wider. It is also found that the spin conductivities oscillate with the Fermi energy and RSOI strength. Specifically, when a magnetic field is present, the spin polarisation can be observed, whereas for the RSOI alone it is zero. Application of such a phenomenon to design a spin polarised electron device based on the graphene material is anticipated.     

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.     

Probing anisotropic superfluidity in atomic Fermi gases with Rashba spin-orbit coupling

Motivated by the prospect of realizing a Fermi gas with a synthetic non-Abelian gauge field, we investigate theoretically a strongly interacting Fermi gas in the presence of a Rashba spin-orbit coupling. As the twofold spin degeneracy is lifted by spin-orbit interaction, bound pairs with mixed singlet and triplet components emerge, leading to an anisotropic superfluid. We calculate the relevant physical quantities, such as the momentum distribution, the single-particle spectral function, and the spin structure factor, that characterize the system.     

Thermoelectric effects in a double-dot Aharonov-Bohm interferometer with Rashba spin-orbit interaction

We investigate the thermoelectric effects in a double-dot Aharonov-Bohm interferometer coupled to ferromagnetic leads held at different temperatures. The interplay of Rashba spin-orbit interaction (RSOI) and magnetic flux ϕ induces various interesting spin-dependent interference phenomena. The thermoelectric transport oscillates with ϕ. The peak of the thermopower S and figure of merit ZT splits into two new peaks and its splitting increases with the Rashba induced phase factor φ _R . With increasing φ _R S and ZT at ϕ = ± 2nπ (n = 0,1,2,...) exhibit a conversion from a peak to a valley. In the presence of the interplay of RSOI and ϕ by increasing spin polarization the splitting peaks of S (ZT) become asymmetric and ZT is greatly enhanced. The influence of the quantum dot levels on thermoelectric effects is also analyzed.     

Electron-dephasing time in a two-dimensional spin-polarized system with Rashba spin-orbit interaction

We calculate the dephasing time tau(phi)(B) of an electron in a two-dimensional system with a Rashba spin-orbit interaction, spin-polarized by an arbitrarily large magnetic field parallel to the layer. tau(phi)(B) is estimated from the logarithmic corrections to the conductivity within a perturbative approach that assumes weak, isotropic disorder scattering. For any value of the magnetic field, the dephasing rate changes with respect to its unpolarized-state value by a universal function whose parameter is 2E(Z)/E(SOI) (E(Z) is the Zeeman energy, while E(SOI) is the spin-orbit interaction), confirming the experimental report published in Phys. Rev. Lett. 94, 186805 (2005). In the high-field limit, when 2E(Z) > E(SOI), the dephasing rate saturates and reaches asymptotically to a value equal to half the spin-relaxation rate.     

Spin filtering in a nonuniform quantum wire with Rashba spin-orbit interaction

We investigate theoretically the spin-polarized electron transport for a wide-narrow-wide (WNW) quantum wire under the modulation of Rashba spin-orbit interaction (SOI). The influence of both the structure of the quantum wire and the interference between different pairs of subbands on the spin-polarized electron transport is taken into account simultaneously via the spin-resolved lattice Green function method. It is found that a very large vertical spin-polarized current can be generated by the SOI-induced effective magnetic field at the structure-induced Fano resonance even in the presence of strong disorder. Furthermore, the magnitude of the spin polarization can be tuned by the Rashba SOI strength and structural parameters. Those results may provide an effective way to design a spin filter device without containing any magnetic materials or applying a magnetic field.     

Rashba and Dresselhaus spin-orbit interaction in semiconductor quantum wells

We theoretically investigate the Rashba and Dresselhaus spin-orbit interaction in AlAs/GaAs/Al_0.3Ga_0.7As/AlAs step-quantum wells. The ratio of Rashba and Dresselhaus spin splitting can be effectively manipulated by the well width and step width in the absence of electric field and magnetic field. When the well width of the step-quantum well is wider than 10 nm, the total spin splitting, which contains the contribution of interface as well as linear and cubic Dresselhaus terms, is always the greatest when the width of GaAs layer equals to about 2 nm. When the well width is wider than 2 nm, two different step widths can meet the SU(2) symmetry conditions, the smaller one of them results in maximum spin relaxation time. We also predict the application of the step-quantum well in spintronic devices.     

Optical properties of BiTeI semiconductor with a strong Rashba spin-orbit interaction

We have modeled the 4f ¹-5d ¹ absorption spectrum of a LiYF₄:Ce³⁺ crystal at zero temperature using a microscopic model of the electron-phonon interaction and the real spectrum of LiYF₄ lattice vibrations. Effects caused by mixing of the wave functions of different states of the 5d ¹ excited configuration of the Ce³⁺ ion, which is induced by the electron-phonon interaction, are considered based on the calculations of the second-, third-, and fourth-order exact moments of curvature of the spectrum envelope. We have shown that the large value of the splitting between the maxima of the bands in the absorption spectrum that correspond to transitions to the third and fourth 5d ¹ levels is a result of the nonadiabatic interaction of 5d electrons with lattice vibrations.     

Spin-polarized transport in adiabatic quantum point contact with strong Rashba spin-orbit interaction

We first report 0.5(2e²/h) conductance quantization in adiabatic quantum point contacts (QPCs) fabricated at high In-content InGaAs/InAlAs single heterojunctions under no magnetic field. This quantization seems difficult to understand, since the spin one-dimensional (1D) subbands in the QPCs are generally degenerated when B=0. However, this observation is reproducible in various QPC samples with different dimensions but not likely so definite as the conductance quantization in usual QPCs. It is noted that this particular heterojunction 2DEG is found to have high electron mobility of <5×10⁵ cm²/Vs as well as very large Rashba spin-orbit (SO) coupling constant of <35×10⁻¹² eVm. So that, the QPCs realized here can be regarded as a kind of Tomonaga-Luttinger wire with an enhanced Rashba interaction. In such a case, a mode coupling between the Rashba splitting 1D subbands gives rise to a spin-polarized transport in each ±k direction. This theory could be the one plausible candidate to explain the 0.5(2e²/h) conductance quantization observed here in the adiabatic QPC. This finding would be developed to novel spin-filters or spin-directional coupler devices based on nonmagnetic semiconductors.     

Spin Hall and spin Nernst effects in graphene with intrinsic and Rashba spin-orbit interactions

The spin Hall and spin Nernst effects in graphene are studied based on Green’s function formalism.We calculate intrinsic contributions to spin Hall and spin Nernst conductivities in the Kane-Mele model with various structures.When both intrinsic and Rashba spin-orbit interactions are present,their interplay leads to some characteristics of the dependence of spin Hall and spin Nernst conductivities on the Fermi level.When the Rashba spin-orbit interaction is smaller than intrinsic spin-orbit coupling,a weak kink in the conductance appears.The kink disappears and a divergence appears when the Rashba spin-orbit interaction enhances.When the Rashba spin-orbit interaction approaches and is stronger than intrinsic spin-orbit coupling,the divergence becomes more obvious.     

Voltage-controllable spin-polarized transport through parallel-coupled double quantum dots with Rashba spin-orbit interaction

A spin device, consisting of parallel-coupled double quantum dots and three normal metal leads, is proposed to realize spin-polarized current without the help of magnetic field and magnetic material. Based on the Keldysh nonequilibrium Green function technique and equation of motion method, the spin-dependent current formula in each lead is derived. It is shown that not only a fully polarized current but also a tunable pure spin current can be obtained by modulating the structure parameters, strength of Rashba spin-orbit interaction and bias voltages properly. It further demonstrates the dependence of the spin-polarized current on the strength of the Rashba spin-orbit interaction.     

Quantum dots with Rashba spin-orbit coupling

We present results on the effects of spin-orbit coupling on the electronic structure of few-electron interacting quantum dots. The ground-state properties as a function of the number of electrons in the dot N are calculated by means of spin-density functional theory. We find a suppression of Hund's rule due to the competition of the Rashba effect and exchange interaction. Introducing an in-plane Zeeman field leads to a paramagnetic behavior of the dot in a closed-shell configuration and to spin texture in space.     

Electron-electron interaction in the magnetoresistance of graphene

We investigate the magnetotransport in large area graphene Hall bars epitaxially grown on silicon carbide. In the intermediate field regime between weak localization and Landau quantization, the observed temperature-dependent parabolic magnetoresistivity is a manifestation of the electron-electron interaction. We can consistently describe the data with a model for diffusive (magneto)transport that also includes magnetic-field-dependent effects originating from ballistic time scales. We find an excellent agreement between the experimentally observed temperature dependence of magnetoresistivity and the theory of electron-electron interaction in the diffusive regime. We can further assign a temperature-driven crossover to the reduction of the multiplet modes contributing to electron-electron interaction from 7 to 3 due to intervalley scattering. In addition, we find a temperature-independent ballistic contribution to the magnetoresistivity in classically strong magnetic fields.     

Rashba spin-orbit interaction and shot noise for spin-polarized and entangled electrons

We study shot noise for spin-polarized currents and entangled electron pairs in a four-probe (beam-splitter) geometry with a local Rashba spin-orbit (s-o) interaction in the incoming leads. Within the scattering formalism we find that shot noise exhibits Rashba-induced oscillations with continuous bunching and antibunching. We show that entangled states and triplet states can be identified via their Rashba phase in noise measurements. For two-channel leads, we find an additional spin rotation due to s-o induced interband coupling which enhances spin control. We show that the s-o interaction deter-mines the Fano factor, which provides a direct way to measure the Rashba coupling constant via noise.     

Universal spin-induced time reversal symmetry breaking in two-dimensional electron gases with Rashba spin-orbit interaction

We have experimentally studied the spin-induced time reversal symmetry (TRS) breaking as a function of the relative strength of the Zeeman energy (E(Z)) and the Rashba spin-orbit interaction energy (E(SOI)), in InGaAs-based 2D electron gases. We find that the TRS breaking, and hence the associated dephasing time tau(phi)(B), saturates when E(Z) becomes comparable to E(SOI). Moreover, we show that the spin-induced TRS breaking mechanism is a universal function of the ratio E(Z)/E(SOI), within the experimental accuracy.     

Anomalous Hall effect in a two-dimensional electron gas with Rashba and Dresselhaus spin-orbit interaction

We discuss the mechanism of the anomalous Hall effect in a Rashba-Dresselhaus two-dimensional electron gas subjected to a homogeneous out-of-plane magnetization. On the basis of a systematic treatment of the kinetic equations for the spin-density matrix, results are derived for the dynamic Hall conductivity in a closed form. Its nonanalytic dependence on both the scattering time and the frequency of the applied electric field is discussed. Except for in a special Rashba-Dresselhaus model, there is a finite intrinsic anomalous Hall effect, which is extremely sensitive to short-range elastic scattering.     

Two-dimensional S-N-S junction with Rashba spin-orbit coupling

The effect of Rashba spin-orbit coupling on the supercurrent in S-2DEG-S proximity junctions is investigated in the clean limit. A generalization of Beenakker’s formula for Andreev levels to the case of spin-orbit scattering is presented. Spin-orbit induced splitting of Andreev bound states is predicted for an infinite-width junction with nonvanishing normal backscattering at S-N interfaces. However, a semiclassical average of the Josephson current is insensitive to the Rashba coupling as long as the electron-electron interaction in 2DEG is neglected. The text was submitted by the authors in English.     

Chiral splitting and polarization-dependent optical absorption of exciton for Rashba spin-orbit interaction

We study theoretically the effect of Rashba spin-orbit interaction (RSOI) on the chiral splitting of quasi-two-dimensional quantum well (QW) exciton. By a nonvariational method, entire energy spectrum is treated simultaneously, it does not require a great deal of insight to choose a good variational function. We show that, the coexistence of electron and hole RSOI introduces a four-energy system for both heavy-hole and light-hole exciton, the competition between them leads to an anticrossing exciton energy spectrum. We also show that the chiral splitting of energy spectrum leads to a polarization-dependent optical absorption. The results suggest a way for direct optical measurements of RSOI parameters.     

Tunneling anisotropic magnetoresistance and spin-orbit coupling in Fe/GaAs/Au tunnel junctions

We report the observation of tunneling anisotropic magnetoresistance effect in the epitaxial metal-semiconductor system Fe/GaAs/Au. The observed twofold anisotropy of the resistance can be switched by reversing the bias voltage, suggesting that the effect originates from the interference of the spin-orbit coupling at the interfaces. Corresponding model calculations reproduce the experimental findings very well.