Spin-orbit coupling and linear crossings of dipolar magnons in van der Waals antiferromagnets

TL;DR

This paper predicts linear crossings in magnon spectra of van der Waals antiferromagnets caused by dipole-dipole interactions, and discusses how these crossings can be gapped, affecting magnon transport.

Contribution

It introduces a magnon spin-orbit coupling mechanism induced by dipole interactions in a specific bilayer honeycomb lattice, revealing phase transitions in magnon spectra.

Findings

Linear crossings occur in magnon spectrum near band minimum and zone boundary.

Gaps can open in crossings when intra- or Kitaev interactions dominate.

Results aid in understanding magnon dynamics and transport in van der Waals antiferromagnets.

Abstract

A magnon spin-orbit coupling, induced by the dipole-dipole interaction, is derived in monoclinic-stacked bilayer honeycomb spin lattice with perpendicular magnetic anisotropy and antiferromagnetic interlayer coupling. Linear crossings are predicted in the magnon spectrum around the band minimum in G valley, as well as in the high frequency range around the zone boundary. The linear crossings in K and K' valleys, which connect the acoustic and optical bands, can be gapped when the intralayer dipole-dipole or Kitaev interactions exceed the interlayer dipole-dipole interaction, resulting in a phase transition from semimetal to insulator. Our results are useful for analyzing the magnon spin dynamics and transport properties in van der Waals antiferromagnet.