Quantization of Spin Circular Photogalvanic Effect in Altermagnetic Weyl Semimetals
Phys. Rev. Lett. 136, 096701 – Published 2 March, 2026
DOI: https://doi.org/10.1103/463y-q7lt
Abstract
We theoretically predict a spin-current analog of the quantized circular photogalvanic effect in Weyl semimetals. This phenomenon is forbidden in antiferromagnets by symmetry but uniquely allowed in altermagnets, highlighting a novel and intrinsic characteristic of altermagnetism. To systematically explore second-order spin current responses, we classify all symmetry-allowed responses based on spin point groups. Furthermore, we provide a comprehensive classification of altermagnetic Weyl semimetals by identifying spin space groups that host symmetry-enforced Weyl points. Utilizing this classification, we construct a symmetry-guided tight-binding model and confirm our predictions. Finally, we identify Weyl crossings in a material candidate via first-principle calculations. Our Letter unveils a distinctive optical response of altermagnets, paving the way for a new frontier in altermagnetism.
