Tunable Van Hove singularities and the magnetization in a two-dimensional electron gas with the spin–orbit interaction in a parallel magnetic field

The problem of finding the single-particle density of states of a two-dimensional electron gas with the spin–orbit interaction in a parallel magnetic field has been solved. It has been shown that, with increasing field, the square-root singularity of the density of states (N(E) ~ 1 / \(\sqrt {E + 1} \)) existing at the minimum energy in zero magnetic field becomes logarithmic (the Van Hove singularity) and is displaced inside the spectrum, and the minimum energy of the spectrum decreases. The presence of two types of spin–orbit interaction (Rashba and Dresselhaus) is responsible for two peaks of the density of states and for an additional step in the density of states at certain directions of the magnetic field. The energy position of these features can be determined from the magnetization of the electron gas. This makes it possible to find the Rashba and Dresselhaus coupling constants.     

Ground states of spin-orbit-coupled Bose Einstein condensates in the presence of external magnetic field

Two different kinds of spin-orbit (SO) coupling are often investigated theoretically and experimentally in atomic Bose-Einstein condensates (BECs), namely, Rashba and Dresselhaus SO couplings. We show that ground states for these two SO-coupled BECs share lots of similarities and it is impossible to distinguish them from the observation of ground states. We find that an Ioffe-Pritchard magnetic field can be utilized as a tool to distinguish them. In the presence of the Ioffe-Pritchard magnetic field, ground states manifest distinctively for the Rashba and Dresselhaus SO-coupled BECs.     

Spin and Majorana polarization in topological superconducting wires

We study a one-dimensional wire with strong Rashba and Dresselhaus spin-orbit coupling (SOC), which supports Majorana fermions when subject to a Zeeman magnetic field and in the proximity of a superconductor. Using both analytical and numerical techniques we calculate the electronic spin texture of the Majorana end states. We find that the spin polarization of these states depends on the relative magnitude of the Rashba and Dresselhaus SOC components. Moreover, we define and calculate a local "Majorana polarization" and "Majorana density" and argue that they can be used as order parameters to characterize the topological transition between the trivial system and the system exhibiting Majorana bound modes. We find that the local Majorana polarization is correlated to the transverse spin polarization, and we propose to test the presence of Majorana fermions in a 1D system by a spin-polarized density of states measurement.     

Current-induced spin accumulation in lateral superlattices with Rashba and Dresselhaus spin–orbit interaction

The current-induced spin accumulation is calculated for a 1D lateral semiconductor superlattice with spin–orbit interaction of the Rashba and Dresselhaus type. Due to its particular symmetry, the Rashba interaction alone only leads to an in-plane component of the magnetization transverse to the applied electric field. When in addition a Dresselhaus contribution is present, this symmetry is lifted, and all components of the magnetization are induced by the electric field. Based on the density-matrix approach, the induced spin polarization is determined as a function of external in-plane electric and magnetic fields.     

Spin texturing in quantum wires with Rashba and Dresselhaus spin–orbit interactions and in-plane magnetic field

In this work, we investigate the effects of interplay of spin–orbit interaction and in-plane magnetic fields on the electronic structure and spin texturing of parabolically confined quantum wire. Numerical results reveal that the competing effects between Rashba and Dresselhaus spin–orbit interactions and the external magnetic field lead to a complicated energy spectrum. We find that the spin texturing owing to the coupling between subbands can be modified by the strength of spin–orbit couplings as well as the magnitude and the orientation angle of the external magnetic field.     

Influence of spin–orbit interaction,Zeeman effect and light polarisation on the electronic and optical properties of pseudo-elliptic quantum rings under magnetic field

ABSTRACT

We theoretically investigated the influences of the magnetic field and light polarisation on the electronic and optical properties of a GaAs/GaAlAs pseudo-elliptic quantum ring, modelled by an outer ellipsis and an inner circle, in the presence of the Rashba and Dresselhaus spin–orbit interactions and Zeeman effect. We show that Aharonov-Bohm oscillations of the energy spectrum are not affected by the presence of the Zeeman effect alone but, in the presence of Rashba and Dresselhaus spin–orbit couplings, the periodicity of certain levels becomes hardly definite. The Zeeman effect generally enhances/diminishes the separation levels produced by Rashba/Dresselhaus interactions (SOI) and when both types of SOI are considered, the effect depends on their relative strength. The magnetic field can trigger spin-flip for each type of spin–orbit interaction and Zeeman effect or their combination through anticrossings in the energy spectra. Our results reveal that the absorption spectra are very sensitive to the magnetic field and light polarisation. For all polarisations considered, the magnetic field increment leads to the redshift or blueshift of some particular peaks (an effect of this ring geometry) and a better separation of the peaks. The x-polarised light determines spectra with many small, but separated peaks while the circular polarised light leads to spectra with large peaks of high amplitude.     

Spin–lattice relaxation phenomena in the magnetic state of a suggested Weyl semimetal CeAlGe

ABSTRACT

In this work, we report the results of DC susceptibility, AC susceptibility and related technique, resistivity, transverse and longitudinal magnetoresistance and heat capacity on polycrystalline magnetic semimetal CeAlGe. This compound undergoes antiferromagnetic type ordering around 5.2 K (T¹). Under the application of external magnetic fields, parallel alignment of magnetic moments is favoured above 0.5?T. At low field and temperature, frequency and AC field amplitude response of AC susceptibility indicate the presence of spin–lattice relaxation phenomena. The observation of spin–lattice interaction suggests the presence of the Rashba–Dresselhaus spin–orbit interaction which is associated with inversion and time-reversal symmetry breaking. Additionally, the presence of negative and asymmetric longitudinal magnetoresistance indicates anomalous velocity contribution to the magnetoresistance due to the Rashba–Dresselhaus spin–orbit interaction which is further studied by heat capacity.     

The effects of Dresselhaus and Rashba spin-orbit interactions on the electron tunneling in a non-magnetic heterostructure

We theoretically investigate the electron transport properties in a non-magnetic heterostructure with both Dresselhaus and Rashba spin-orbit interactions. The detailed-numerical results show that (1) the large spin polarization can be achieved due to Dresselhaus and Rashba spin-orbit couplings induced splitting of the resonant level, although the magnetic field is zero in such a structure, (2) the Rashba spin-orbit coupling plays a greater role on the spin polarization than the Dresselhaus spin-orbit interaction does, and (3) the transmission probability and the spin polarization both periodically change with the increase of the well width.     

Zero field spin splitting in asymmetric quantum wells

Spin splitting of asymmetric quantum wells is theoretically investigated in the absence of any electric field, including the contribution of interface-related Rashba spin-orbit interaction as well as linear and cubic Dresselhaus spin-orbit interaction. The effect of interface asymmetry on three types of spin-orbit interaction is discussed. The results show that interface-related Rashba and linear Dresselhaus spin-orbit interaction can be increased and cubic Dresselhaus spin-orbit interaction can be decreased by well structure design. For wide quantum wells, the cubic Dresselhaus spin-orbit interaction dominates under certain conditions, resulting in decreased spin relaxation time.     

Spin-flip transport in one-dimensional comb-like waveguide

The spin-flip transport of electron in one-dimensional comb-like waveguide structures is investigated theoretically including the Rashba and Dresselhaus effects. The spin-polarized transmission of electron oscillates with changing the length of stubs and/or electronic momentum, and depends sensitively on electron spin orientation injected from the ferromagnetic source. The spin-flip transmission induced by the Rashba and Dresselhaus effects can only be up to 25% in the case of one stub, and can be enhanced significantly by adding more stubs. The spin-flip transmission induced by the Dresselhaus effect is similar to what induced by the Rashba effect for the one stub case, but is quite different for multi-stub case. The interplay between the Rashba and Dresselhaus effects shortens the period of transmission oscillation and enhances the splitting of the transmission peaks.     

Orbital mechanisms of electron-spin manipulation by an electric field

A theory of spin manipulation of quasi-two-dimensional (2D) electrons by a time-dependent gate voltage applied to a quantum well is developed. The Dresselhaus and Rashba spin-orbit coupling mechanisms are shown to be rather efficient for this purpose. The spin response to a perpendicular-to-plane electric field is due to a deviation from the strict 2D limit and is controlled by the ratios of the spin, cyclotron, and confinement frequencies. The dependence of this response on the magnetic field direction is indicative of the strengths of the competing spin-orbit coupling mechanisms.     

Determination of the Rashba and Dresselhaus coupling constants using the conductance of a ballistic nanowire

We study the conductance steps of a ballistic nanowire in the presence of a harmonic potential, an in-plane magnetic field, and spin–orbit interactions induced by Rashba and Dresselhaus effects. Calculations of the conductance, at low temperature, using the Landauer–Büttiker formalism, reveal different patterns of steps that are strongly dependent on the magnetic field. Such dependence provides a powerful tool for determining the strengths of the spin–orbit interaction independently, especially in nanowires with low carrier density.     

The nondissipative spin Hall current in a nonuniform Rashba effect system

The spin Hall current in a two-dimensional electron system with nonuniform Rashba spin–orbit interaction (SOI) is investigated by means of the lattice Green's function method. Large electric and spin Hall currents are produced by this nonuniform Rashba SOI, while the electric Hall current vanishes in the uniform Rashba SOI system. A nondissipative spin Hall current is also produced, without any longitudinal voltage bias, any external magnetic field and any special class of band insulators.     

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.     

Magnetic moment of a two-dimensional degenerate electron gas in mesoscopic samples

The orbital magnetism of two-dimensional electrons in mesoscopic samples is studied in models where the interaction between electrons is neglected. Various geometries are considered as there are disc, plaquette, bracelet with hard wall confinement and also a confinement with a parabolic potential. We calculate the average magnetic moment which means an average with respect to size fluctuations and de Haas-van Alphen oscillations which arise in the case of a sharp Fermi cutoff. We see three distinct ranges in the magnetic field: (i) small field region where perturbation theory applies; (ii) moderate fields where edge currents play a prominent role; and (iii) the high field range with a Landau type susceptibility. In a quasiclassical picture, the electronic orbits are not qualitatively changed by a magnetic field in (i); skipping orbits are important in (ii); and in (iii), the cyclotron radius is smaller than the sample size. As a rule, we find an enhancement of the magnetic response which increases with k_FL, that is, with sample size divided by the Fermi wave length. Also, we have found out that the quasiclassical approximation fails in the calculation of the magnetic properties; on the other hand, we have seen no essential differences between the canonical ensemble (fixed particle number) and the grand canonical ensemble (chemical potential given). In the case of plaquettes, in particular for samples in the form of squares, we have found agreement with experimental results by Lévy, Reich, Pfeiffer and West.     

Spin Splitting in Different Semiconductor Quantum Wells

We theoretically investigate the spin splitting in four undoped asymmetric quantum wells in the absence of external electric field and magnetic field. The quantum well geometry dependence of spin splitting is studied with the Rashba and the Dresselhaus spin-orbit coupling included. The results show that the structure of quantum well plays an important role in spin splitting. The Rashba and the Dresselhaus spin splitting in four asymmetric quantum wells are quite different. The origin of the distinction is discussed in this work.     

Spin separation in cyclotron motion

Charged carriers with different spin states are spatially separated in a two-dimensional hole gas. Because of strong spin-orbit interaction, holes at the Fermi energy in GaAs have different momenta for two possible spin states traveling in the same direction, and, correspondingly, different cyclotron orbits in a weak magnetic field. Two point contacts, acting as a monochromatic source of ballistic holes and a narrow detector arranged in the magnetic focusing geometry are demonstrated to work as a tunable spin filter.     

Electron-spin polarization in a non-magnetic heterostructure

The spin dependent electron transmission through a non-magnetic III-V semiconductor symmetric well is studied theoretically so as to investigate the output transmission current polarization at zero magnetic field. Transparency of electron transmission is calculated as a function of electron energy as well as the well width, within the one electron band approximation along with the spin-orbit interaction. Enhanced spin-polarized resonant tunneling in the heterostructure due to Dresselhaus and Rashba spin-orbit coupling induced splitting of the resonant level is observed. We predict that a spin-polarized current spontaneously emerges in this heterostructure. This effect could be employed in the fabrication of spin filters, spin injectors and detectors based on non-magnetic semiconductors.     

Spin inverter and polarizer curved nanowire driven by Rashba and Dresselhaus spin–orbit interactions

We propose in theory a curved nanowire structure that can both serve as a spin inverter and a spin polarizer driven by a periodic Rashba spin–orbit coupling (SOC) and a uniform Dresselhaus SOC. The curved section of the U-shaped quasi-one dimensional nanowire with an arc of radius R and circumferential length $\pi R$ is divided into segments of equal length initially having only its inherent homogeneous Dresselhaus SOC. Then a Rashba-type SOC is applied at every alternating segment. By tuning the Rashba SOC strength and the incident electron energy, this device can flip the spin at the output of an incoming spin-polarized electron. On the other hand, this same device acts as a spin filter for an unpolarized input for which an outgoing electron with a non-zero polarization can be achieved without the application of an external magnetic field. Moreover, the potential modulation caused by the periodic Rashba SOC enables this device to function as an attenuator for a certain range of incident electron energies that can make the probability current density drop to 10⁻⁴ of its otherwise magnitude in other regimes.