Antiferromagnetic magnon pseudospin: Dynamics and diffusive transport

TL;DR

This paper develops a pseudospin formalism to describe the dynamics and diffusive transport of antiferromagnetic magnons, accounting for material anisotropies and interactions, and relates it to recent experimental observations.

Contribution

It introduces a pseudospin-based theoretical framework for antiferromagnetic magnon transport, unifying bosonic mode interactions with spin dynamics.

Findings

Pseudospin formalism accurately describes magnon transport in anisotropic antiferromagnets.

The approach explains recent non-local spin transport experiments.

Formalism is applicable to other coupled bosonic systems.

Abstract

We formulate a theoretical description of antiferromagnetic magnons and their transport in terms of an associated pseudospin. The need and strength of this formulation emerges from the antiferromagnetic eigenmodes being formed from superpositions of spin-up and -down magnons, depending on the material anisotropies. Consequently, a description analogous to that of spin-1/2 electrons is demonstrated while accounting for the bosonic nature of the antiferromagnetic eigenmodes. Introducing the concepts of a pseudospin chemical potential together with a pseudofield and relating magnon spin to pseudospin allows a consistent description of diffusive spin transport in antiferromagnetic insulators with any given anisotropies and interactions. Employing the formalism developed, we elucidate the general features of recent non-local spin transport experiments in antiferromagnetic insulators hosting magnons with different polarisations. The pseudospin formalism developed herein is valid for any pair of coupled bosons and is likely to be useful in other systems comprising interacting bosonic modes.