Quantized circular photogalvanic effect in Weyl semimetals

TL;DR

This paper predicts a quantized circular photogalvanic effect in Weyl semimetals and related materials, linking it directly to topological charges and enabling experimental detection of Weyl node monopole charges.

Contribution

It demonstrates that in certain Weyl semimetals and Rashba materials, the CPGE trace is effectively quantized and directly measures the topological charge of Weyl points, with minimal material dependence.

Findings

CPGE trace is quantized in Weyl semimetals.

Quantization relates to fundamental constants and topological charge.

Large CPGE magnitude allows experimental detection of Weyl monopole charge.

Abstract

The circular photogalvanic effect (CPGE) is the part of a photocurrent that switches depending on the sense of circular polarization of the incident light. It has been consistently observed in systems without inversion symmetry and depends on non-universal material details. Here we find that in a class of Weyl semimetals (e.g. SrSi$_2$) and three-dimensional Rashba materials (e.g. doped Te) without inversion and mirror symmetries, the injection contribution to the CPGE trace is effectively quantized in terms of the fundamental constants $e, h, c$ and $\epsilon_0$ with no material-dependent parameters. This is so because the CPGE directly measures the topological charge of Weyl points, and non-quantized corrections from disorder and additional bands can be small over a significant range of incident frequencies. Moreover, the magnitude of the CPGE induced by a Weyl node is relatively large, which enables the direct detection of the monopole charge with current techniques.