# Observation of Topological Photocurrents in the Chiral Weyl Semimetal RhSi

## TL;DR

This study demonstrates the observation of topological photocurrents in the chiral Weyl semimetal RhSi, confirming theoretical predictions that relate the photocurrent to the Weyl nodes' topological charge, with potential implications for topological photonics.

## Contribution

First experimental verification of the topological circular photogalvanic effect in a chiral Weyl semimetal, matching theoretical predictions based on Berry monopole charge.

## Key findings

- Photocurrent spectrum matches theoretical predictions.
- Response observed in a low-energy window up to 0.65 eV.
- Results confirm the topological origin of the photocurrent.

## Abstract

Weyl semimetals are crystals in which electron bands cross at isolated points in momentum space. Associated with each crossing point (or Weyl node) is an integer topological invariant known as the Berry monopole charge. The discovery of new classes of Weyl materials is driving the search for novel properties that derive directly from the Berry charge. The circular photogalvanic effect (CPGE), whereby circular polarized light generates a current whose direction depends on the helicity of the absorbed photons, is a striking example of a macroscopic property that emerges from Weyl topology. Recently, it was predicted that the rate of current generation associated with optical transitions near a Weyl node is proportional to its monopole charge and independent of material-specific parameters. In Weyl semimetals that retain mirror symmetry this universal photogalvanic current is strongly suppressed by opposing contributions from energy equivalent nodes of opposite charge. However, when all mirror symmetries are broken, as in chiral Weyl systems, nodes with opposite topological charge are no longer degenerate, opening a window of photon energies where the topological CPGE can emerge. In this work we test this theory through measurement of the photon-energy dependence of the CPGE in the chiral Weyl semimetal RhSi. The spectrum is fully consistent with a topological CPGE, as it reveals a response in a low-energy window that closes at 0.65 eV, in quantitative agreement with the theoretically-derived bandstucture.