Spin-orbit induced longitudinal spin-polarized currents in non-magnetic solids

TL;DR

This paper predicts and analyzes the occurrence of spin-polarized longitudinal currents in certain non-magnetic solids with low symmetry, using a group-theoretical approach that considers spin-orbit interaction and crystal symmetry.

Contribution

It introduces a universal symmetry-based formalism for analyzing spin conductivity tensors in non-magnetic solids, extending beyond the two-current model.

Findings

Longitudinal spin-polarized currents can occur in non-magnetic low-symmetry solids.

The spin conductivity tensor is governed by the magnetic Laue group.

Numerical examples show longitudinal spin conductivity can match transverse conductivity in magnitude.

Abstract

For certain non-magnetic solids with low symmetry the occurrence of spin-polarized longitudinal currents is predicted. These arise due to an interplay of spin-orbit interaction and the particular crystal symmetry. This result is derived using a group-theoretical scheme that allows investigating the symmetry properties of any linear response tensor relevant to the field of spintronics. For the spin conductivity tensor it is shown that only the magnetic Laue group has to be considered in this context. Within the introduced general scheme also the spin Hall- and additional related transverse effects emerge without making reference to the two-current model. Numerical studies confirm these findings and demonstrate for (Au$_{1-x}$Pt$_{\rm x}$)$_4$Sc that the longitudinal spin conductivity may be in the same order of magnitude as the conventional transverse one. The presented formalism only relies on the magnetic space group and therefore is universally applicable to any type of magnetic order.