Chern numbers of topological phonon band crossing determined with inelastic neutron scattering

TL;DR

This study demonstrates a novel spectroscopic method combining inelastic neutron scattering and ab initio calculations to directly determine Chern numbers of topological phonon band crossings in certain crystals, revealing their topological properties.

Contribution

It introduces a new approach to measure Chern numbers of phonon band crossings directly using neutron scattering data, expanding topological classification tools beyond electronic systems.

Findings

Identified topological phonon band crossings in MnSi and CoSi.

Established a relation between Chern numbers and scattering intensity modulation.

Method can determine large Chern numbers with sufficient resolution.

Abstract

Topological invariants in the band structure, such as Chern numbers, are crucial for the classification of topological matters and dictate the occurrence of exotic properties, yet their direct spectroscopic determination has been largely limited to electronic bands. Here, we use inelastic neutron scattering in conjunction with ab initio calculations to identify a variety of topological phonon band crossings in MnSi and CoSi single crystals. We find a distinct relation between the Chern numbers of a band-crossing node and the scattering intensity modulation in momentum space around the node. Given sufficiently high resolution, our method can be used to determine arbitrarily large Chern numbers of topological phonon band-crossing nodes.