Persistent spin current in spin-orbit coupling systems in the absence of an external magnetic field

TL;DR

This paper predicts the existence of a persistent spin current in spin-orbit coupled systems at equilibrium without external magnetic fields, highlighting a novel phenomenon where spin flows without charge currents or accumulation.

Contribution

It introduces the concept of persistent spin currents in equilibrium in spin-orbit systems, especially demonstrating this in a two-dimensional quantum wire, which is a new insight.

Findings

Persistent spin current exists at equilibrium without magnetic fields.

Spin current flows along the confined direction due to spin precession.

Charge current and spin accumulation are zero despite the spin flow.

Abstract

The spin-orbit coupling systems with a zero magnetic field is studied under the equilibrium situation, {\it i.e.}, without a voltage bias. A persistent spin current is predicted to exist under most circumstances, although the persistent charge current and the spin accumulation are identically zero. In particular, a two-dimensional quantum wire is investigated in detail. Surprisingly, a persistent spin current is found to flow along the confined direction, due to the spin precession in accompany with the particle motion. This provides an interesting example of constant spin flowing without inducing a spin accumulation, contrary to common intuition.