# Fermi arc plasmons in Weyl semimetals

## TL;DR

This paper explores the unique chiral surface plasmons called Fermi arc plasmons in Weyl semimetals, revealing their hyperbolic dispersion and potential for highly directional surface plasmon beams.

## Contribution

It introduces the concept of Fermi arc plasmons in Weyl semimetals and characterizes their hyperbolic, chiral dispersion relations and directional propagation properties.

## Key findings

- Fermi arc plasmons are chiral with hyperbolic dispersion.
- Support for a wide range of surface plasmon wave vectors.
- Potential for launching highly directional surface plasmon beams.

## Abstract

In the recently discovered Weyl semimetals, the Fermi surface may feature disjoint, open segments -- the so-called Fermi arcs -- associated with topological states bound to exposed crystal surfaces. Here we show that the collective dynamics of electrons near such surfaces sharply departs from that of a conventional three-dimensional metal. In magnetic systems with broken time reversal symmetry, the resulting Fermi arc plasmons (FAPs) are chiral, with dispersion relations featuring open, hyperbolic constant frequency contours. As a result, a large range of surface plasmon wave vectors can be supported at a given frequency, with corresponding group velocity vectors directed along a few specific collimated directions. Fermi arc plasmons can be probed using near field photonics techniques, which may be used to launch highly directional, focused surface plasmon beams. The unusual characteristics of FAPs arise from the interplay of bulk and surface Fermi arc carrier dynamics, and give a window into the unusual Fermiology of Weyl semimetals.