Theory of electric-field-induced spin accumulation and spin current in the two-dimensional Rashba model

TL;DR

This paper systematically analyzes electric-field-induced spin accumulation and spin current in the 2D Rashba model using a spin-density-matrix approach, revealing resonances, clarifying definitions, and addressing previous ambiguities.

Contribution

It introduces a physically well-founded definition of spin current and clarifies its relation to spin accumulation, differing from prior results and resolving ambiguities in the Rashba model.

Findings

Resonances in spin excitations frequency domain.

Spin-Hall conductivity diverges logarithmically at low frequencies.

Close relation between spin accumulation and spin current due to quasi-chemical potential.

Abstract

Based on the spin-density-matrix approach, both the electric-field-induced spin accumulation and the spin current are systematically studied for the two-dimensional Rashba model. Eigenmodes of spin excitations give rise to resonances in the frequency domain. Utilizing a general and physically well-founded definition of the spin current, we obtain results that differ remarkably from previous findings. It is shown that there is a close relationship between the spin accumulation and the spin current, which is due to the prescription of a quasi-chemical potential and which does not result from a conservation law. Physical ambiguities are removed that plagued former approaches with respect to a spin-Hall current that is independent of the electric field. For the clean Rashba model, the intrinsic spin-Hall conductivity exhibits a logarithmic divergency in the low-frequency regime.