Spontaneous Crystal Thermal Hall Effect in Insulating Altermagnets

TL;DR

This paper predicts a thermal Hall effect in certain insulating altermagnets with specific symmetries, driven by magnon Berry curvature, controllable by magnetic orientation and strain, and discusses potential material candidates.

Contribution

It introduces the concept of a crystal thermal Hall effect in altermagnets and demonstrates how it can be controlled and observed in specific materials.

Findings

Finite thermal Hall conductivity predicted for altermagnetic insulators.

Magnon Berry curvature leads to controllable thermal Hall response.

Material candidates like MnF₂, CoF₂, and NiF₂ identified for experiments.

Abstract

We show that magnetic insulators with a collinear and compensated order can exhibit a thermal Hall effect even at zero magnetic field if they have altermagnetic symmetries. We predict a finite thermal Hall conductivity vector $\boldsymbol{\kappa}_\text{H}$ for a rutile-inspired effective spin model with Dzyaloshinskii-Moriya interaction. Within the linear spin-wave theory, we identify two magnon branches that carry identical Berry curvature and give rise to a finite $\boldsymbol{\kappa}_\text{H}$, which can be controlled by the N\'eel vector orientation and by strain. The thermal Hall response is further complemented with a spin Nernst response to contrast spin and heat transport in altermagnetic insulators with those in ferromagnets and antiferromagnets. Our results establish the crystal thermal Hall effect of magnons and we discuss material candidates for experimental realization, such as MnF$_2$, CoF$_2$, and NiF$_2$.