# Sound of Fermi arcs

## TL;DR

This paper investigates the collective charge excitations of Fermi arcs in Weyl semimetals, revealing gapless, linearly dispersing plasmon modes influenced by surface state penetration and anisotropy, with implications for their electron liquid behavior.

## Contribution

It introduces a theoretical analysis of Fermi arc plasmons in Weyl semimetals, highlighting their unique gapless and linear dispersion characteristics due to surface state penetration and anisotropic effects.

## Key findings

- Fermi arc plasmons are gapless and linearly dispersing.
- Surface state penetration influences plasmon gaplessness.
- Fermi arc electron liquid exhibits mixed 1D and 2D characteristics.

## Abstract

Using Green's function of semi-infinite Weyl semimetals we find that the collective charge excitations of Fermi arcs in undoped Weyl semi-metals are linearly dispersing gapless plasmon modes. The gaplessness comes from proper consideration of the deep penetration of surface states at the end of Fermi arcs into the interior of Weyl semimetal. The linear dispersion -- rather than square root dispersion of {\it pure 2D} electron systems with extended Fermi surface -- arises from the strong anisotropy introduced by the Fermi arc itself, due to which the continuum of surface particle-hole excitations in this system will have strong resemblence to the one-dimensional electron systems. This places the Fermi arc electron liquid in between the 1D and 2D electron liquids. Contamination with the particle-hole excitations of the bulk gives rise to the damping of the Fermi arc sounds.