Steady-state spin densities and currents

TL;DR

This review discusses steady-state spin densities and currents in materials with strong spin-orbit interactions, emphasizing band structure effects, spin precession, and extrinsic phenomena like skew scattering and side jump.

Contribution

It provides a comprehensive overview of how spin precession influences steady-state spin phenomena, integrating both intrinsic and extrinsic effects with recent theoretical and experimental insights.

Findings

Spin densities arise from conserved spin components during precession.

Spin currents are generated by continually precessing spin components.

Extrinsic effects like skew scattering are significantly affected by spin precession.

Abstract

This article reviews steady-state spin densities and spin currents in materials with strong spin-orbit interactions. These phenomena are intimately related to spin precession due to spin-orbit coupling which has no equivalent in the steady state of charge distributions. The focus will be initially on effects originating from the band structure. In this case spin densities arise in an electric field because a component of each spin is conserved during precession. Spin currents arise because a component of each spin is continually precessing. These two phenomena are due to independent contributions to the steady-state density matrix, and scattering between the conserved and precessing spin distributions has important consequences for spin dynamics and spin-related effects in general. In the latter part of the article extrinsic effects such as skew scattering and side jump will be discussed, and it will be shown that these effects are also modified considerably by spin precession. Theoretical and experimental progress in all areas will be reviewed.