The reciprocal interconversion between spin polarization and charge current (CSC) is the focus of intensive theoretical and experimental investigation in spintronics research. Its physical origin stems from the Rashba spin-orbit coupling (SOC) induced by the breaking of the structure inversion symmetry. The steady-state interconversion efficiency is the result of the non-trivial spin textures of the electric-field distorted Fermi surface. Its full understanding and evaluation requires the consideration of disorder-induced relaxation effects in the presence of spin-orbit induced band splitting. In this paper the additional effect of the orbital degree of freedom is analyzed in a two-subband quantum well with both conventional and unconventional Rashba SOC in the presence of disorder impurity scattering. The latter is treated at the level of the Born approximation in the Green’s function self-energy and with the inclusion of vertex corrections in the linear response functions for the charge current and the spin polarization. By explicitly considering the symmetry properties of the Hamiltonian the matrix structure of the correlation functions is shown to decompose in independent blocks of symmetry-related physical observables. We find that the inclusion of vertex corrections is important for the correct estimate of the CSC efficiency, which also depends on the position of the Fermi level. We also find that the relative sign of the Rashba SOC in the two subbands plays a key role in determining the behavior of the CSC. Finally, we point out how the two-subband model compares with the standard single-band two-dimensional electron gas.
Spin-charge coupled dynamics is the subject of fundamental and applied research for its relevance in spintronics. In this context the understanding of the interplay between disorder and spin-orbit coupling (SOC) plays a key role. The nonlinear sigma model for disordered electron systems is a powerful effective field theory for transport phenomena in diffusive conductors and superconductors. At the tree level the nonlinear sigma model is equivalent to the Eilenberger and Usadel equations for the quasiclassical Keldysh Green function. The latter, which were originally developed for superconductors, have been extended in order to include SOC.
Here we derive the nonlinear sigma model with Rashba SOC for the disordered two-dimensional electron gas (2DEG). By starting from a functional integral representation of the partition function for disordered fermions in the presence of Rashba SOC, we introduce the Q matrix (in Keldysh and spin space) field to decouple the effective fermion-fermion interaction introduced by the disorder average. After integrating out the fermion degrees of freedom, we get the effective action for the Q field. The saddle-point approximation reproduces the self-consistent Born approximation, in the presence of Rashba SOC. By restricting to the manifold QQ=1, we derive the nonlinear sigma model for diffusive spin and charge density modes. The Rashba SOC appears as a SU(2) gauge field coupled to the Q field. Nonuniform and time-dependent saddle-point solutions for the Q field obey the Usadel equation in the presence of Rashba SOC.
Finally, extensions of the theory beyond the 2DEG are briefly discussed.
We evaluate the non-equilibrium spin polarization induced by an applied electric field for a tight-binding model of electron states at oxides interfaces in LAO/STO heterostructures. By a combination of analytic and numerical approaches we investigate how the spin texture of the electron eigenstates due to the interplay of spin-orbit coupling and inversion asymmetry determines the sign of the induced spin polarization as a function of the chemical potential or band filling, both in the absence and presence of local disorder. With the latter, we find that the induced spin polarization evolves from a non monotonous behavior at zero temperature to a monotonous one at higher temperature. Our results may provide a sound framework for the interpretation of recent experiments.
The spin Hall effect (SHE) and the inverse spin Hall effect (ISHE) are well established phenomena in current spintronics research. A third important effect is the current-induced spin polarization, which, within the Rashba model for a spin-orbit coupled two-dimensional disordered electron gas, has been predicted by Edelstein in 1990 and it is referred to as the Edelstein effect (EE). This effect is deeply connected to the above two effects thanks to a constraint dictated by the equation of motion. Less known is the inverse Edelstein effect (IEE), which is the Onsager reciprocal of the EE and according to which a charge current is generated by a non-equilibrium spin polarization. The IEE has been recently observed (Nature Commun. 4, 2944 (2013)) in a hybrid ferromagnetic-metal system. In this talk I provide a precise microscopic definition of the IEE and its description within the Rashba model. It turns out that the effect has a surprisingly simple interpretation when the spin-charge coupled drift-diffusion equations governing it are cast in the language of a SU(2) gauge theory, with the Rashba spin-orbit coupling playing the role of a generalized spin-dependent vector potential. After sketching briefly the derivation of the drift-diffusion equations, the latter are applied to the interpretation of the experiments. The role of spin-orbit coupling due to impurities is also considered, by showing that the strenght of the IEE can be controlled by the ratio of the spin relaxation rates associated to the two type of spin-orbit coupling.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.