# Ab initio theory of the spin-dependent conductivity tensor and the spin Hall effect in random alloys

## TL;DR

This paper extends relativistic electron transport theory to include spin-dependent conductivity, enabling analysis of the spin Hall effect in random alloys, with applications to Pt-based alloys showing promising spin conversion efficiency.

## Contribution

It introduces a formalism for the spin-dependent conductivity tensor in random alloys, including the Fermi sea term, and applies it to analyze the spin Hall effect in Pt alloys.

## Key findings

- Spin Hall conductivity has intrinsic and extrinsic contributions with different concentration dependencies.
- Selected Pt alloys exhibit sizable spin Hall angles around 0.2.
- Alloys like Pt-Re and Pt-Ta are promising for efficient charge-to-spin conversion.

## Abstract

We present an extension of the relativistic electron transport theory for the standard (charge) conductivity tensor of random alloys within the tight-binding linear muffin-tin orbital method to the so-called spin-dependent conductivity tensor, which describes the Kubo linear response of spin currents to external electric fields. The approach is based on effective charge- and spin-current operators, that correspond to intersite electron transport and that are nonrandom, which simplifies the configuration averaging by means of the coherent potential approximation. Special attention is paid to the Fermi sea term of the spin-dependent conductivity tensor, which contains a nonzero incoherent part, in contrast to the standard conductivity tensor. The developed formalism is applied to the spin Hall effect in binary random nonmagnetic alloys, both on a model level and for Pt-based alloys with an fcc structure. We show that the spin Hall conductivity consists of three contributions (one intrinsic and two extrinsic) which exhibit different concentration dependences in the dilute limit of an alloy. Results for selected Pt alloys (Pt-Re, Pt-Ta) lead to the spin Hall angles around 0.2; these sizable values are obtained for compositions that belong to thermodynamically equilibrium phases. These alloys can thus be considered as an alternative to other systems for efficient charge to spin conversion, which are often metastable crystalline or amorphous alloys.