Universal optical conductivity of a disordered Weyl semimetal

TL;DR

This paper shows that optical conductivity can serve as a universal, experimentally measurable order parameter to distinguish between semimetallic and metallic phases in disordered Weyl semimetals, revealing critical behavior during the quantum phase transition.

Contribution

It demonstrates that optical conductivity exhibits universal scaling behavior across the disorder-driven semimetal-metal transition in Weyl semimetals, independent of impurity details.

Findings

Optical conductivity acts as an order parameter for the phase transition.

Correction to dielectric constant and optical conductivity is impurity-independent.

Optical conductivity reveals critical properties and universality class of the transition.

Abstract

Topological Weyl semimetals, besides manifesting chiral anomaly, can also accommodate a disorder-driven unconventional quantum phase transition into a metallic phase. A fundamentally and practically important question in this regard concerns an experimentally measurable quantity that can clearly distinguish these two phases. We show that the optical conductivity while serving this purpose can also play the role of a bonafide order parameter across such disorder-driven semimetal-metal quantum phase transition by virtue of displaying distinct scaling behavior in semimetallic and metallic phases, as well as inside the quantum critical fan supporting a non-Fermi liquid. We demonstrate that the correction to dielectric constant and optical conductivity in a dirty Weyl semimetal due to weak disorder is independent of the actual nature of point-like impurity scatterers. Therefore, optical conductivity can be used as an experimentally measurable quantity to study the critical properties and to pin the universality class of the disorder-driven quantum phase transition in Weyl semimetals.