Magnon thermal Hall effect in collinear antiferromagnets

TL;DR

This paper theoretically investigates the magnon thermal Hall effect in collinear antiferromagnets, revealing that broken symmetries and Dzyaloshinskii-Moriya interactions enable a non-zero effect even without external magnetic fields.

Contribution

It introduces a theoretical model showing how symmetry breaking and Dzyaloshinskii-Moriya interactions induce magnon thermal Hall effect in antiferromagnets.

Findings

Thermal Hall effect occurs in compensated Néel order without external magnetic field.

Dzyaloshinskii-Moriya interaction causes spin-momentum splitting of magnons.

External electric fields can modify the magnon thermal Hall effect.

Abstract

In this paper we theoretically discuss thermal Hall effect of magnons in insulating N\'{e}el ordered antiferromagnets at zero external magnetic field. We show that for compensated N\'{e}el order the non-zero thermal Hall effect will occur in the absence of any symmetry between the two magnetic sublattices, thus making the system ferrimagnetic. We then show that collinear Dzyaloshinskii's weak ferromagnets, in which there is a symmetry connecting the magnetic sublattices, also show magnon thermal Hall effect. The thermal Hall effect of magnons will be non-zero by a virtue of the spin-momentum splitting of the magnon spectrum due to the Dzyaloshinskii-Moriya interaction as well as second-nearest exchange interaction different in the two magnetic sublattices, both corresponding to the broken symmetries that lead to the Dzyaloshinskii's invariant. We construct a theoretical model in which an external electric field may change the symmetry of the antiferromagnetic system thus altering the thermal Hall effect of magnons.