Interactions remove the quantization of the chiral photocurrent at Weyl points

TL;DR

This paper investigates how Coulomb and Hubbard interactions affect the quantized chiral photocurrent in Weyl semimetals, revealing that interactions break the quantization and introduce observable corrections.

Contribution

It demonstrates that interactions perturbatively break the quantization of the CPGE in Weyl semimetals, challenging the notion of topological protection.

Findings

Interactions break the quantization of the chiral photocurrent.

Corrections are larger than those in graphene's optical conductivity.

Observable frequency dependence of the interaction corrections.

Abstract

The chiral photocurrent or circular photogalvanic effect (CPGE) is a photocurrent that depends on the sense of circular polarization. In a disorder-free, noninteracting chiral Weyl semimetal, the magnitude of the effect is approximately quantized with a material-independent quantum $e^3/h^2$ for reasons of band topology. We study the first-order corrections due to the Coulomb and Hubbard interactions in a continuum model of a Weyl semimetal in which known corrections from other bands are absent. We find that the inclusion of interactions generically breaks the quantization. The corrections are similar but larger in magnitude than previously studied interaction corrections to the (nontopological) linear optical conductivity of graphene, and have a potentially observable frequency dependence. We conclude that, unlike the quantum Hall effect in gapped phases or the chiral anomaly in field theories, the quantization of the CPGE in Weyl semimetals is not protected but has perturbative corrections in interaction strength.