Dipolar optical plasmon in thin-film Weyl semimetals

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 time-reversal symmetry-broken Weyl semimetal thin films will host a single ω∝q plasmon mode that results from collective, antisymmetric charge oscillations between the two surfaces, in stark contrast to conventional 2D bilayers as well as Dirac semimetals with Fermi arcs, which support antisymmetric 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.