Transport and thermodynamic properties of a 2DEG in the presence of tilted magnetic field: the influence of Dresselhauss interaction

The effect of Dresselhauss spin-orbit coupling on transport and thermodynamic properties of a non-interacting two-dimensional electron gas (2DEG) is investigated. The Hamiltonian used also includes a tilted magnetic field and a Rashba spin-orbit interaction. The Dresselhauss spin-orbit interaction, likewise the Rashba spin-orbit interaction, introduces a beating pattern in the conductivity tensor and in the magnetization along the field direction. A method to estimate the contribution of the Rashba and Dresselhauss interactions to the beating pattern is given using the periodicity of the beating patterns.     

Spin Hall effect in Sr2RuO4 and transition metals (Nb,Ta)

We study the intrinsic spin Hall conductivity (SHC) and the d-orbital Hall conductivity (OHC) in metallic d-electron systems based on the multiorbital tight-binding model. The obtained Hall conductivities are much larger than that in p-type semiconductors. The origin of these huge Hall effects is the “effective Aharonov-Bohm phase” induced by the signs of inter-orbital hopping integrals as well as atomic spin-orbit interaction. Huge SHC and OHC due to this mechanism is ubiquitous in multiorbital transition metals.     

Magnetoquantum transport in a modulated 2D electron gas with spin-orbit interaction

We investigate the effects of spin-orbit interaction (SOI) and plane-perpendicular magnetic field on the conductivity of a two-dimensional electron system in the presence of one-dimensional electrostatic modulation. The calculations are performed when a low-intensity, low-frequency external electric field is applied. The Kubo formula for the conductivity is employed in the calculation. The single-particle eigenstates which depend on the strengths of the magnetic field, the SOI and modulation potential, are calculated and then used to determine the conductivity. We present numerical results for the conductivity along the channels as well as the tunneling conductivity perpendicular to the constrictions as functions of the modulation potential, the SOI and the magnetic field. We demonstrate that the effect of finite frequency is to related to the reduction of both the longitudinal and transverse conductivities.     

Baryon-baryon spin-orbit interaction in a quark model

The baryon-baryon spin-orbit interactions are studied within the framework of a nonrelativistic quark-cluster model. The origin of the spin-orbit interactions is taken to be the Galilei-invariant part of the spin-orbit term in the one-gluon-exchange potential between quarks. It gives, for example, the NN spin-orbit interaction which is qualitatively similar to the empirical ones. The baryon-nucleus spin-orbit interactions are also considered along this line. The N- and Σ-nucleus spin-orbit interactions are of comparable strength, while the Λ-nucleus spin-orbit interaction is weak. The main origin of the difference between the Λ -nucleus and Σ-nucleus spin-orbit interactions is the presence of the comparatively strong antisymmetric LS (ALS) terms for both NΛ and NΣ interactions but with opposite signs. Other sources of the spin-orbit interactions are briefly discussed in connection with the problem of the spin-orbit effect in the excited baryon spectra.     

Effect of the spin-orbit interaction on the thermodynamic properties of crystals: specific heat of bismuth

We discuss measurements and ab initio calculations of the specific heat for crystalline bismuth, strictly speaking, a semimetal but in the temperature region accessible to us (T>2 K) acting as a semiconductor. We extend experimental data available in the literature and notice that the ab initio calculations without spin-orbit interaction exhibit a maximum at approximately 8 K, about 20% lower than the measured one. Inclusion of spin-orbit interaction decreases the discrepancy markedly: the maximum of C(T) is now only 7% larger than the measured one. Exact agreement is obtained if the strength of the spin-orbit Hamiltonian is reduced by a factor of approximately 0.9. We also discuss the dependence of the lattice parameter and the cohesive energy on spin-orbit interaction.     

Quantum corrections to the conductivity in systems with strong spin-orbit splitting of the spectrum

Quantum corrections to the conductivity in a 2D system with a smooth random potential and strong spin-orbit splitting of the spectrum are studied. It is shown that the interference correction is positive and, right down to very low temperatures, does not exceed in magnitude the negative correction due to the electron-electron interaction. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 4, 314–319 (25 August 1998)     

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-Hall conductivity in electron-phonon coupled systems

We derive the ac spin-Hall conductivity sigmasH(omega) of two-dimensional spin-orbit coupled systems interacting with dispersionless phonons of frequency omega0. For the linear Rashba model, we show that the electron-phonon contribution to the spin-vertex corrections breaks the universality of sigmasH(omega) at low frequencies and provides a nontrivial renormalization of the interband resonance. On the contrary, in a generalized Rashba model for which the spin-vertex contributions are absent, the coupling to the phonons enters only through the self-energy, leaving the low-frequency behavior of sigmasH(omega) unaffected by the electron-phonon interaction.     

Vertex corrections to the anomalous Hall effect in spin-polarized two-dimensional electron gases with a Rashba spin-orbit interaction

We study the effect of disorder on the intrinsic anomalous Hall conductivity in a magnetic two-dimensional electron gas with a Rashba-type spin-orbit interaction. We find that anomalous Hall conductivity vanishes unless the lifetime is spin-dependent, similar to the spin Hall conductivity in the nonmagnetic system. In addition, we find that the spin Hall conductivity does not vanish in the presence of magnetic scatterers.     

Baryon-baryon spin-orbit and tensor interactions from quark-exchange kernels

Dibaryon quark-exchange kernels are constructed in explicit analytic form for the tensor and spin-orbit terms of the one-gluon-exchange quark-quark Breit interaction and for spin-orbit terms generated by quark-confinement mechanisms. The spin operators needed are defined through their spin-reduced matrix elements including those needed for interactions coupling NN, NΔ, and ΔΔ channels. Effective baryon-baryon spin-orbit potentials, generated through the Wigner transforms of the quark-exchange kernels with the use of a local momentum approximation, show that the NN spin-orbit interaction derived from the symmetric spin-orbit term of the one-gluon-exchange quark-quark interaction is in general agreement with the short-range part of phenomenological potentials derived from NN scattering. With the inclusion of the antisymmetric spin-orbit one-gluon-exchange terms and spin-orbit terms generated by confining potentials the full triplet-odd NN spin-orbit potential is greatly reduced in the 0.5–1 fm range. The uncertainties associated with spin-orbit terms generated by quark-confinement mechanisms are emphasized. The relative importance of various possible quark-gluon exchange terms is studied and shows that models which neglect some types of exchange terms are open to question. An SU(3)-flavor symmetric model for N-hyperon spin-orbit potentials leads to an NΛ spin-orbit potential only slightly weaker than the NN spin-orbit potential.     

Effects of absorbed hydrogen on the electronic properties of (Zr2Fe)(1-x)H(x) metallic glasses

The electrical conductivity (σ) of hydrogen doped (Zr(2)Fe)(1-x)H(x) metallic glasses has been measured in the temperature range from 290 down to 5 K. The decrease of the room temperature conductivity and the increase of its temperature coefficient are explained as consequences of increased disorder due to hydrogen doping. σ(T) for (Zr(2)Fe)(1-x)H(x) metallic glasses at low temperatures decreases with the increase of temperature, forming a minimum at T(min), before it starts a monotonic increase with increasing temperature. Both the functional forms and the magnitudes of the observed σ(T) are interpreted in terms of weak localization, electron-electron interaction and spin-fluctuation effects. Our results reveal that the electron-phonon scattering rate varies with the square of temperature from low temperatures up to 100 K and changes behaviour to a linear form at higher temperatures. At low temperatures, the minimum in σ(T) is shifted to higher temperatures, which is ascribed to the increase of the screening parameter of the Coulomb interaction F* associated with the enhancement of the spin fluctuations arising from the increase of the hydrogen doping. The spin-orbit scattering rate and the electron diffusion constant are reduced by hydrogen doping.     

Phase diagram of the spin Hall effect

We obtain analytic formulas for the frequency-dependent spin-Hall conductivity of a two-dimensional electron gas (2DEG) in the presence of impurities, linear spin-orbit Rashba interaction, and external magnetic field perpendicular to the 2DEG. We show how different mechanisms (skew scattering, side jump, and spin precession) can be brought in or out of focus by changing controllable parameters such as frequency, magnetic field, and temperature. We find, in particular, that the dc spin-Hall conductivity vanishes in the absence of a magnetic field, while a magnetic field restores the skew-scattering and side jump contributions proportionally to the ratio of magnetic and Rashba fields.     

Effects of geometry and linearly polarized cavity photons on charge and spin currents in a quantum ring with spin-orbit interactions

We calculate the persistent charge and spin polarization current inside a finite-width quantum ring of realistic geometry as a function of the strength of the Rashba or Dresselhaus spin-orbit interaction. The time evolution in the transient regime of the two-dimensional (2D) quantum ring connected to electrically biased semi-infinite leads is governed by a time-convolutionless non-Markovian generalized master equation. The electrons are correlated via Coulomb interaction. In addition, the ring is embedded in a photon cavity with a single mode of linearly polarized photon field, which is polarized either perpendicular or parallel to the charge transport direction. To analyze carefully the physical effects, we compare to the analytical results of the toy model of a one-dimensional (1D) ring of non-interacting electrons with spin-orbit coupling. We find a pronounced charge current dip associated with many-electron level crossings at the Aharonov-Casher phase ΔΦ = π, which can be disguised by linearly polarized light. Qualitative agreement is found for the spin polarization currents of the 1D and 2D ring. Quantitatively, however, the spin polarization currents are weaker in the more realistic 2D ring, especially for weak spin-orbit interaction, but can be considerably enhanced with the aid of a linearly polarized electromagnetic field. Specific spin polarization current symmetries relating the Dresselhaus spin-orbit interaction case to the Rashba one are found to hold for the 2D ring, which is embedded in the photon cavity.     

The tensor part of Skyrme's interaction

A tensor part is added to central and spin-orbit parts of Skyrme's effective interaction and its contribution to the Hartree-Fock spin-orbit coupling of spherical spin-unsaturated nuclei is analysed. Minor improvements to spin-orbit splittings can be achieved if the strengths of the tensor interaction are treated as free parameters, but the fit to experiment deteriorates if the tensor interaction contribution is estimated for a realistic interaction.     

Gauge potential formulations of the spin Hall effect in graphene

Two different gauge potential methods are engaged to calculate explicitly the spin Hall conductivity in graphene. The graphene Hamiltonian with spin-orbit interaction is expressed in terms of kinematic momenta by introducing a gauge potential. A formulation of the spin Hall conductivity is established by requiring that the time evolution of this kinematic momentum vector vanishes. We then calculated the conductivity employing the Berry gauge fields. We show that both of the gauge fields can be deduced from the pure gauge field arising from the Foldy-Wouthuysen transformations.     

Spin gunn effect

We predict that the flow of unpolarized current in electron-doped GaAs and InP at room temperature is unstable at high electric fields to the dynamic formation of spin-polarized current pulses. Spin-polarized current is spontaneously generated because the conductivity of a spin-polarized electron gas differs from that of an unpolarized electron gas, even in the absence of spin-orbit interaction. Magnetic fields are not required for the generation of these spin-polarized current pulses, although they can help align the polarization of sequential pulses along the same axis.     

Theory of magnetooptical effects in thin ferromagnetic films

A systematic theory is derived for the anomalous magnetooptical effects in thin ferromagnetic films for the more general case in which conduction electrons are scattered by both phonons and impurities. The Kohn-Luttinger density-matrix method is used to find the tensor for the complex transverse conductivity, which is linear in the spin-orbit interaction and can be used to find the magnetooptical parameter. The temperature dependences of the real and imaginary parts of the conductivity tensor are found for high temperatures.     

Role of spin-flip transitions in the anomalous Hall effect of FePt alloy

We carry out ab?initio calculations which demonstrate the importance of the non-spin-conserving part of the spin-orbit interaction for the intrinsic anomalous Hall conductivity of ordered FePt alloys. The impact of this interaction is strongly reduced if Pt is replaced by the lighter isoelectronic element Pd. An analysis of the interband transitions responsible for the anomalous velocity reveals that spin-flip transitions occur not only at avoided band crossings near the Fermi level, but also between well-separated pairs of bands with similar dispersions. We also predict a strong anisotropy in the anomalous Hall conductivity of FePt caused entirely by low-frequency spin-flip transitions.     

RGM calculation of the NN spin-orbit interaction in a quark model

A quark-cluster model supplemented by an effective-meson-exchange potential (EMEP) is applied to the NN ³P scattering using the resonating group method (RGM). The repulsive central and the attractive spin-orbit NN interactions are obtained from the quark-exchange interaction including the symmetric spin-orbit term in the one-gluon-exchange potential. When the long- and medium-range central and tensor forces between nucleons are introduced as the EMEP, the results obtained seem to explain a considerable part of the empirical spin-orbit effect in the ³P scattering phase shifts.     

Spin current and polarization in impure two-dimensional electron systems with spin-orbit coupling

We derive the transport equations for two-dimensional electron systems with Rashba spin-orbit interaction and short-range spin-independent disorder. In the limit of slow spatial variations, we obtain coupled diffusion equations for the electron density and spin. Using these equations we calculate electric-field induced spin accumulation and spin current in a finite-size sample for an arbitrary ratio between spin-orbit energy splitting Delta and elastic scattering rate tau(-1). We demonstrate that the spin-Hall conductivity vanishes in an infinite system independent of this ratio.