Spin force and the generation of sustained spin current in time-dependent Rashba and Dresselhauss systems

TL;DR

This paper investigates how time-dependent Rashba and Dresselhaus spin-orbit couplings in a 2DEG generate and sustain spin currents, revealing the relation between spin force and current, and demonstrating maximum spin current at specific modulation frequencies.

Contribution

It introduces a non-Abelian gauge field approach to relate Lorentz spin force with spin current and shows sustained spin currents in time-dependent SOC systems even with impurity scattering.

Findings

Longitudinal spin force induces transverse spin current.

Universal spin Hall conductivity of e/8π for constant Rashba SOC.

Maximum ac spin current occurs at modulation frequency matching Larmor frequency.

Abstract

The generation of spin current and spin polarization in a 2DEG 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 $\frac e{8\pi}$, derived previously via the Berry phase and semiclassical 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.