Nonlinear Optomagnetic Signature of d -Wave Altermagnets

Altermagnetism, a recently discovered collinear magnetic order with net zero magnetization but exhibiting spin-splitting band structure, has attracted much research interest due to the rich fundamental physics and possible applications. In this Letter, we investigate the optomagnetic response of d-wave altermagnets, focusing on the inverse Cotton-Mouton effect-the induction of static magnetization via linearly polarized light. We find that the direction of the induced magnetization is determined by the Néel vector. Moreover, its magnitude exhibits a periodic dependence on the polarization angle of the incident light, a hallmark of the system's symmetry. Our findings demonstrate that the inverse Cotton-Mouton effect offers a direct method both for detecting d-wave altermagnets and for probing their intrinsic properties.