Nonexistence of intrinsic spin currents

TL;DR

This paper demonstrates that intrinsic spin currents do not exist in electron systems with spin-orbit interaction, showing that observed spin currents are extrinsic and depend on impurity scattering.

Contribution

The study reveals that spin currents are extrinsic, arising only beyond the Born approximation, challenging the notion of intrinsic spin currents in spin-orbit coupled systems.

Findings

Spin current is zero within the Born approximation.

Spin currents depend explicitly on impurity scattering.

Intrinsic spin currents do not exist in the studied models.

Abstract

We have described the electron spin dynamics in the presence of the spin-orbit interaction and disorder using the spin-density matrix method. We showed that in the Born approximation in the scattering amplitude the spin current is zero for an arbitrary ratio of the spin-orbit splitting and the scattering rate. Various types of the disorder potential are studied. We argue that the bulk spin current has always an {\it extrinsic} nature and depends explicitely on scattering by impurities since it appears only beyond the Born approximation in the scattering amplitude.