Plasmon-polaron of the topological metallic surface states

TL;DR

This paper introduces a novel low-frequency plasmon-polaron mode on topological metallic surfaces, arising from strong electron-phonon interactions, with potential implications for topological protection and surface state dynamics.

Contribution

It reports the discovery and analysis of a new plasmon-polaron mode in topological surface states, highlighting its origin, properties, and experimental observation.

Findings

Identification of a new low-frequency acoustic plasmon mode

Mode exhibits topological protection with suppressed scattering

Experimental observation in Be2Se3 confirms theoretical predictions

Abstract

We report a plasmon-polaron mode of a 2D electron gas occupying surface states of a 3D topological crystal. This new, low-frequency, acoustic plasmon mode splits-off from the conventional spin-plasmon mode as a result of strong interactions of the surface electrons with bulk phonons. We show that, like in the case of the conventional spin-plasmon, the scattering of this mode is strongly suppressed in some regions of the phase space. This signature of the topological protection leads to an Umklapp-free mode dispersion at the Brillouin zone boundary. Such a plasmon polaron mode has indeed been recently observed in the topological metal Be2Se3.