Nonlinear Photocurrent as a Probe of Magnetic Structures and Magnetoelectric Switching in Altermagnet

Altermagnets (AMs), a newly recognized class of collinear magnets characterized by the alternating spin splitting of energy bands, offer a promising platform for spintronics and nonlinear optoelectronics. However, identifying their distinct magnetic configurations and detecting the coupled magnetoelectric order remains challenging. Here, we establish a second-order photocurrent as a reliable, symmetry-sensitive probe for both the magnetic structures and ferroelectric switching in AMs. Based on relativistic magnetic point group analysis and ab-initio calculations in the exemplary altermagnetic material MnSe, we reveal distinct photocurrent fingerprints for its three different magnetic configurations. In particular, within the 3.5-4.0 eV photon energy range, the normal shift current exhibits magnetic configuration-dependent current directions. Notably, ferroelectric switching flips the directions of the normal shift current and injection current, enabling optical readout of magnetoelectric states. Our results demonstrate that second-order photocurrents can serve as sensitive probes for both the magnetic structures and magnetoelectric states in altermagnetic materials.