Weyl excitations and topological surface states via helicon-phonon mixing

Helicons are low-frequency almost transverse electromagnetic waves supported by electron gas in the presence of external magnetic field. In metals and doped semiconductors their anisotropic dispersion relation can be tuned to intersect with the dispersion curves for acoustic or optical phonons that favors the formation of hybrid helicon-phonon modes. Previously, interactions with longitudinal phonons have been routinely disregraded since they are small at low angles between helicon wavevector and magnetic filed direction and completely vanishes if they are aligned. In the present paper we reconsider the formation of helicon-phonon waves and argue that the corresponding intersections between dispersion curves for the hybrid modes are the topologically protected Weyl points. We discus their possible manifestations and demonstrate the presence of topologically protected arc states.