Symmetry-Breaking Magneto-Optical Effects in Altermagnets

The recently discovered altermagnets (AMs) are promising for novel spintronics, while experimentally distinguishing them, especially yet-synthesized two-dimensional candidates, from conventional antiferromagnets (AFMs) remains a challenge. Here, we investigate strain-engineered magneto-optical responses in AMs and reveal the underlying mechanism with a crystal-field picture. Symmetry analysis reveals that uniaxial strain can selectively break rotation or mirror symmetries in AMs while preserving PT symmetry in AFMs, thereby activating distinct magneto-optical responses (e.g., optical absorption and Kerr rotation) unique to AMs. First-principles calculations across prototypical systems, including a semiconducting V₂Se₂O monolayer and metallic CrSb bulk, show that the strain-induced optical signatures are significant enough for conventional optical measurements. Our work establishes a rapid, noninvasive characterization methodology for altermagnetism across material platforms, accelerating its exploration for spin-based technologies.