Experimental observation of quantized circular photogalvanic effect in Weyl semimetals

Demonstrate, under experimentally controlled conditions, the quantized circular photogalvanic effect in Weyl semimetals with energy-offset Weyl nodes, and verify that the photocurrent magnitude is determined by the Chern number of a single Weyl node, thereby establishing the predicted quantization of the CPGE.

Background

The circular photogalvanic effect (CPGE) generates a dc photocurrent from circularly polarized light in noncentrosymmetric materials. Theory predicts that in certain Weyl semimetals where opposite-chirality Weyl nodes reside at different energies, the CPGE becomes quantized and directly tied to a topological invariant (the single-node Chern number).

Despite theoretical proposals, a definitive experimental observation of this quantized CPGE has not yet been reported, making its verification a key goal for connecting topological band geometry with nonlinear optical responses.