Semiclassical theory of spin-orbit torques in disordered multiband electron systems

We study spin-orbit torques (SOT) in non-degenerate multiband electron systems in the weak disorder limit. In order to have better physical transparency a semiclassical Boltzmann approach equivalent to the Kubo diagrammatic approach in the non-crossing approximation is formulated. This semiclassical framework accounts for the interband- coherence effects induced by both the electric field and static impurity scattering. Using the two-dimensional Rashba ferromagnet as a model system, we show that the antidamping-like SOT arising from disorder-induced interband-coherence effects is very sensitive to the spin structure of disorder and may have the same sign as the intrinsic SOT in the presence of spin-dependent disorder. While the cancellation of this SOT and the intrinsic one occurs only in the case of spin-independent short-range disorder.Comment: 10 pages, 2 figures, accepted by Physical Review

Unconventional thermoelectric behaviors and enhancement of figure of merit in Rashba spintronic systems

Thermoelectric transport in strongly spin-orbit coupled two-dimensional Rashba system is studied using the exact solution of the linearized Boltzmann equation. Some unusual transport behaviors are revealed. We show that the electrical conductivity takes a Drude form when the Fermi energy $E_{F}$ is above the band crossing point, but a non-Drude form which is a quadratic function of $E_{F}$ when $E_{F}$ lies below the band crossing point. The Mott relation breaks down when $E_{F}$ lies in the vicinity of the band crossing point. It is shown that the thermopower and thermoelectric figure of merit are strongly enhanced when $E_{F}$ downs below the band crossing point. This enhancement is attributed to not only the one-dimensional-like density of state but also the unconventional intraband elastic scattering below the band crossing point. The differences between these results and those obtained by the relaxation time approximation are discussed in detail.Comment: 9 pages, 5 figure

Thermoelectric response of spin polarization in Rashba spintronic systems

Motivated by recent discovery of strongly spin-orbit coupled two-dimensional (2D) electron gas near the surface of Rashba semiconductors BiTeX (X=Cl, Br, I), we calculate thermoelectric responses of spin polarization in 2D Rashba model using an exact solution of the linearized Boltzmann equation for elastic scattering. When the Fermi energy $E_{F}$ lies below the band crossing point we find a non-Edelstein electric-field induced spin polarization which is linear in $E_{F}$. We show that the Mott-like relation between spin polarizations induced by the temperature gradient and electric field breaks down significantly when $E_{F}$ lies in the vicinity of the band crossing point. As the temperature tends to zero, the temperature-gradient induced spin polarization vanishes. These results differ from previous ones obtained by relaxation time approximations.Comment: 9 pages, 3 figure