Dynamical density response and optical conductivity in topological metals

TL;DR

This paper investigates the electromagnetic response of three-dimensional topological metals with Weyl or Dirac nodes, revealing unique features like propagating chiral density modes and an additional optical conductivity peak linked to the chiral anomaly.

Contribution

It extends previous studies by systematically analyzing the electromagnetic response of topological metals, highlighting observable signatures of the chiral anomaly such as new propagating modes and optical conductivity features.

Findings

Propagating chiral density modes exist even in weak magnetic fields.

Optical conductivity shows an extra peak due to the chiral anomaly.

Spectral weight of the peak shifts from high frequencies, width relates to chiral charge relaxation.

Abstract

Topological metals continue to attract attention as novel gapless states of matter. While there by now exists an exhaustive classification of possible topologically nontrivial metallic states, their observable properties, that follow from the electronic structure topology, are less well understood. Here we present a study of the electromagnetic response of three-dimensional topological metals with Weyl or Dirac nodes in the spectrum, which systematizes and extends earlier pioneering studies. In particular, we argue that a smoking-gun feature of the chiral anomaly in topological metals is the existence of propagating chiral density modes even in the regime of weak magnetic fields. We also demonstrate that the optical conductivity of such metals exhibits an extra peak, which exists on top of the standard metallic Drude peak. The spectral weight of this peak is transferred from high frequencies and its width is proportional to the chiral charge relaxation rate.