The generation of spin current and spin polarization in a two-dimensional electron gas structure is
studied in the presence of Dresselhaus and Rashba spin-orbit couplings (SOC), the strength of the
latter being modulated in time by an ac gate voltage. By means of the non-Abelian gauge field
approach, we established the relation between the Lorentz spin force and the spin current in the
SOC system, and showed that the longitudinal component of the spin force induces a transverse
spin current. For a constant (time-invariant) Rashba system, we recover the universal spin Hall
conductivity of e
8p, derived previously via the Berry phase and semi-classical methods. In the case
of a time-dependent SOC system, the spin current is sustained even under strong impurity
scattering. We evaluated the ac spin current generated by a time-modulated Rashba SOC in the
absence of any dc electric field. The magnitude of the spin current reaches a maximum when the
modulation frequency matches the Larmor frequency of the electrons.
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Copyright (2014) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in J. Appl. Phys. 115, 183705 (2014) and may be found at http://dx.doi.org/10.1063/1.4876226.