Optical conductivity of an interacting Weyl liquid in the collisionless regime

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 $\ddot{I}ƒ(\hat{I}\text{c◯})=\ddot{I}{ƒ}_0(\hat{I}\text{c◯})\left[1+\frac{1}{N+1}\right]$, where of $\ddot{I}{ƒ}_0(\hat{I}\text{c◯})=N{e}_0^2\hat{I}\text{c◯}/(12hv)$ is the OC in the non-interacting system, with $v$ as the actual (renormalized) Fermi velocity of Weyl quasiparticles at frequency $\hat{I}\text{c◯}$, 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.

21 Pages, 1 Figure: Published Version in PRB