Observation of Double Weyl Phonons in Parity-Breaking FeSi

TL;DR

This study reports the first experimental observation of double-Weyl phonons in parity-breaking FeSi, confirming theoretical predictions and opening new avenues for exploring topological bosonic excitations.

Contribution

The paper provides the first direct measurement of double-Weyl phonons in FeSi, validating theoretical models and demonstrating FeSi as a platform for topological bosonic states.

Findings

Observation of double-Weyl points in FeSi

Agreement between experimental data and theoretical calculations

FeSi as an ideal material for topological bosonic excitations

Abstract

Condensed matter systems have now become a fertile ground to discover emerging topological quasi-particles with symmetry protected modes. While many studies have focused on Fermionic excitations, the same conceptual framework can also be applied to bosons yielding new types of topological states. Motivated by the recent theoretical prediction of double-Weyl phonons in transition metal monosilicides [Phys. Rev. Lett. 120, 016401 (2018)], we directly measured the phonon dispersion in parity-breaking FeSi using inelastic x-ray scattering. By comparing the experimental data with theoretical calculations, we make the first observation of double-Weyl points in FeSi, which will be an ideal material to explore emerging Bosonic excitations and its topologically non-trivial properties.