Optical conductivity of an interacting Weyl liquid in the collisionless regime

TL;DR

This paper demonstrates that long-range Coulomb interactions cause a universal increase in optical conductivity in 3D Weyl semimetals, depending only on the number of Weyl nodes, revealing fundamental quantum-critical effects.

Contribution

It reveals a universal correction to optical conductivity in Weyl semimetals due to Coulomb interactions, linked to quantum-criticality and violation of hyperscaling.

Findings

Universal correction to OC depends only on number of Weyl nodes

Long-range Coulomb interaction enhances OC in a universal manner

Local interactions produce non-universal corrections

Abstract

Optical conductivity (OC) can serve as a measure of correlation effects in a wide range of condensed matter systems. We here show that the long-range tail of the Coulomb interaction yields a universal correction to the OC in a three-dimensional Weyl semimetal $\sigma(\Omega)=\sigma_0(\Omega)\left[ 1+\frac{1}{N+1} \right]$, where of $\sigma_0(\Omega)=Ne^2_0 \Omega/(12 h v)$ is the OC in the non-interacting system, with $v$ as the actual (renormalized) Fermi velocity of Weyl quasiparticles at frequency $\Omega$, and $e_0$ is the electron charge in vacuum. Such universal enhancement of OC, which depends only on the number of Weyl nodes near the Fermi level ($N$), is a remarkable consequence of an intriguing conspiracy among the quantum-critical nature of an interacting Weyl liquid, marginal irrelevance of the long-range Coulomb interaction and the violation of hyperscaling in three dimensions, and can directly be measured in recently discovered Weyl as well as Dirac materials. By contrast, a local density-density interaction produces a non-universal correction to the OC, stemming from the non-renormalizable nature of the corresponding interacting field theory.