Topological magnons in a collinear altermagnet

TL;DR

This paper introduces a model of topological magnons in a collinear altermagnet on a honeycomb lattice, revealing novel magnon topological properties and effects such as the magnon spin Nernst effect and a topologically induced gyromagnetic ratio.

Contribution

It presents a new model for Weyl and nodal-line magnons in altermagnets without DMI, highlighting the role of symmetry breaking and topology in magnon behavior.

Findings

Magnon bands exhibit Weyl and nodal-line features in the model.

The model predicts a nonzero magnon spin Nernst effect under temperature gradients.

A differential gyromagnetic ratio induced by magnon topology is calculated.

Abstract

We propose a model with Weyl magnons and nodal-line magnons ($\mathbb{Z}_2$) in a collinear altermagnet on the honeycomb lattice. Altermagnetic magnon bands can be realized by breaking the symmetry of the second nearest neighbor exchange couplings without the Dzyaloshinskii-Moriya interaction (DMI). In addition to the Chern number and $\mathbb{Z}_2$ invariant, chirality is important to describe the magnon topology. The model shows the nonzero magnon spin Nernst effect when a longitudinal temperature gradient exists. We calculate the differential gyromagnetic ratio induced purely by the topology of altermagnetic magnons, which can be probed through the Einstein-de Haas (EdH) effect.