Acoustic plasmons in type-I Weyl semimetals

TL;DR

This paper studies the collective electromagnetic excitations in type-I Weyl semimetals, revealing gapless acoustic plasmons that could influence superconductivity and plasmonic phenomena.

Contribution

It demonstrates the existence of weakly damped acoustic plasmons in type-I Weyl semimetals and analyzes their properties and potential effects.

Findings

Existence of gapless acoustic plasmons in type-I Weyl semimetals.

Acoustic plasmons are weakly damped and propagate along [001].

Potential implications for superconductivity and plasmon instabilities.

Abstract

Massless chiral fermions emergent in inversion symmetry-breaking Weyl semimetals (WSMs) reside in the vicinity of multiple low symmetry nodes and thus acquire strongly anisotropic dispersion. We investigate the longitudinal electromagnetic modes of two-component degenerate Weyl plasma relevant to the realistic band structure of type-I WSM. We show that the actual spectrum of three dimensional collective density excitations in TaAs family of WSM is gaples due to emergence of acoustic plasmons corresponding to out-of-phase oscillations of the plasma components. These modes exist around the [001] crystallographic direction and are weakly damped, thanks to large difference in the Weyl velocities of the $W_1$ and $W_2$ quasiparticles when propagating along [001]. We show that acoustic plasmons can manifest themselves as slow beatings of electric potential superimposed on fast plasmonic oscillations upon charge relaxation. The revealed acoustic modes can stimulate purely electronic superconductivity, collisionless plasmon instabilities, and formation of Weyl soundarons.