Magnonic Weyl semimetal in pyrochlore ferromagnets

TL;DR

This paper demonstrates that pyrochlore ferromagnets with Dzyaloshinskii-Moriya interaction can host magnonic Weyl semimetal states, featuring topologically protected surface states and Fermi arcs similar to electronic Weyl semimetals.

Contribution

It introduces the concept of magnonic Weyl semimetals in pyrochlore ferromagnets, revealing topological magnon band crossings and surface states.

Findings

Magnonic Weyl nodes occur at specific points in momentum space.

Fermi arcs appear on sample surfaces due to topologically protected states.

Additional Weyl nodes can be generated with anisotropic exchange interactions.

Abstract

Topological states of matter have been a subject of intensive studies in recent years because of their exotic properties such as the topologically protected edge and surface states. The initial studies were exclusively for electron systems. It is now known that topological states can also exist for other particles. Indeed, topologically protected edge states have already been found for phonons and photons. In spite of active searching for topological states in many fields, the studies in magnetism are relatively rare although topological states are apparently important and useful in magnonics. Here we show that the pyrochlore ferromagnets with the Dzyaloshinskii-Moriya interaction are intrinsic magnonic Weyl semimetals. Similar to the electronic Weyl semimetals, the magnon bands in a magnonic Weyl semimetal are nontrivially crossing in pairs at special points (called Weyl nodes) in momentum space. The equal energy contour around the Weyl nodes gives rise to the Fermi arcs on sample surfaces due to the topologically protected surface states between each pair of Weyl nodes. Additional Weyl nodes and Fermi arcs can be generated in lower energy magnon bands when an anisotropic exchange interaction is introduced.