A magneto-optical signature for detecting altermagnetism

Identifying altermagnets is difficult because they host symmetry-enforced spin-split bands without net magnetization. We compute magneto-optical absorption of circularly polarized light for a mean-field altermagnet with Rashba spin-orbit coupling in a perpendicular magnetic field. Landau quantization plus the spin splitting yields helicity-selective transitions that generate extra absorption lines, present only when both altermagnetism and Rashba coupling are included. These lines shift with field and show clear circular dichroism, providing a direct fingerprint of the altermagnetic spin-split band structure and a practical route to detect it.