Weyl excitations via helicon-phonon mixing in conducting materials

TL;DR

This paper predicts the emergence of Weyl excitations in conducting materials under magnetic fields due to helicon-phonon hybridization, revealing new topological phenomena detectable via scattering experiments.

Contribution

It introduces a novel mechanism for Weyl excitations arising from helicon-phonon interactions in conducting materials, expanding the understanding of topological quasiparticles.

Findings

Weyl excitations result from helicon and phonon hybridization.

Optical phonon-related Weyl excitations can be observed in X-ray and Raman scattering.

Topologically protected surface states form due to these Weyl excitations.

Abstract

Quasiparticles with Weyl dispersion can display an abundance of novel topological, thermodynamic and transport phenomena, which is why novel Weyl materials and platforms for Weyl physics are being intensively looked for in electronic, magnetic, photonic and acoustic systems. We demonstrate that conducting materials in magnetic fields generically host Weyl excitations due to the hybridisation of phonons with helicons, collective neutral modes of electrons interacting with electromagnetic waves propagating in the material. Such Weyl excitations are, in general, created by the interactions of helicons with longitudinal acoustic phonons. An additional type of Weyl excitation in polar crystals comes from the interaction between helicons and longitudinal optical phonons. Such excitations can be detected in X-ray and Raman scattering experiments. The existence of the Weyl excitations involving optical phonons in the bulk of the materials also leads to the formation of topologically protected surface arc states that can be detected via surface plasmon resonance.