Weyl magnons in breathing pyrochlore antiferromagnets

TL;DR

This paper predicts the existence of Weyl magnons—topologically protected magnon band crossings—in breathing pyrochlore antiferromagnets, suggesting they can be manipulated experimentally and may lead to new magnetic excitation phenomena.

Contribution

It introduces Weyl magnons in breathing pyrochlore antiferromagnets and discusses their experimental manipulation and detection, expanding the understanding of topological magnetic excitations.

Findings

Weyl magnon band crossings are predicted in the model.

Chiral magnon surface states form arcs at finite energy.

Weyl points can be manipulated in situ by applied fields.

Abstract

Frustrated quantum magnets not only provide exotic ground states and unusual magnetic structures, but also support unconventional excitations in many cases. Using a physically relevant spin model for a breathing pyrochlore lattice, we discuss the presence of topological linear band crossings of magnons in antiferromagnets. These are the analogs of Weyl fermions in electronic systems, which we dub Weyl magnons. The bulk Weyl magnon implies the presence of chiral magnon surface states forming arcs at finite energy. We argue that such antiferromagnets present a unique example in which Weyl points can be manipulated in situ in the laboratory by applied fields. We discuss their appearance specifically in the breathing pyrochlore lattice, and give some general discussion of conditions to find Weyl magnons and how they may be probed experimentally. Our work may inspire a re-examination of the magnetic excitations in many magnetically ordered systems.