Dipolar optical plasmon in thin-film Weyl semimetals

TL;DR

This paper predicts a unique optical plasmon mode in thin-film Weyl semimetals caused by surface charge oscillations, distinct from conventional systems, with potential applications in plasmonics.

Contribution

It introduces the existence of a single $ ext{omega} o ext{sqrt}(q)$ plasmon mode in Weyl semimetal thin-films, derived analytically and verified numerically, highlighting topological surface state effects.

Findings

Weyl semimetal thin-films support a unique optical plasmon mode.

The plasmon mode results from anti-symmetric surface charge oscillations.

The mode is in the particle-hole continuum gap, making it spectroscopically observable.

Abstract

In a slab geometry with large surface-to-bulk ratio, topological surface states such as Fermi arcs for Weyl or Dirac semimetals may dominate their low-energy properties. We investigate the collective charge oscillations in such systems, finding striking differences between Weyl and conventional electronic systems. Our results, obtained analytically and verified numerically, predict that the Weyl semimetal thin-film host a single $\omega\propto \sqrt{q}$ plasmon mode, that results from collective, anti-symmetric charge oscillations of between the two surfaces, in stark contrast to conventional 2D bi-layers as well as Dirac semimetals with Fermi arcs, which support anti-symmetric acoustic modes along with a symmetric optical mode. These modes lie in the gap of the particle-hole continuum and are thus spectroscopically observable and potentially useful in plasmonic applications.