Chirality-dependent spin polarization in metals: linear and quadratic responses

TL;DR

This paper investigates how structural chirality in metals influences spin polarization induced by electric currents, revealing both linear and quadratic responses and explaining the sign discrepancy in quadratic responses.

Contribution

It uncovers the mechanisms of chirality-dependent spin polarization in metals, including bulk and interface effects, and clarifies the origin of sign differences in quadratic responses.

Findings

Spin polarization occurs in the bulk and near interfaces with different responses.

The sign of quadratic response spin polarization is opposite to that of the bulk spin current.

Charge distribution dipoles cause the sign discrepancy in quadratic responses.

Abstract

We study spin polarization induced by locally injected electric currents in a metal whose spin--orbit coupling reflects its structural chirality. We reveal both spin polarization in the bulk in the linear response and antiparallel spin polarization near the interface in the quadratic response to external electric currents, and reproduce the experimentally observed correlation between the chirality of the metal and the direction of spin polarization. In particular, we elucidate that the sign of the spin polarization in the quadratic response is opposite to that expected from the bulk spin current. This sign discrepancy originates from spin polarization induced by dipole-like charge distribution appearing in the quadratic response.