Spin-Flip Optical Excitations in van der Waals Antiferromagnet CrPS4.

We investigate the near-infrared optical response of the semiconducting van der Waals antiferromagnet CrPS4 and identify previously unreported spin-entangled optical resonances. The strong and anisotropic magnetic-field dependence of these resonances reflects the underlying magnetic order and confirms the biaxial antiferromagnetic nature of CrPS4. From the magnetic field evolution of the optical transition, we extract key magnetic parameters, including the spin-flop (≈0.9 T) and spin-saturation (≈8 T) fields. These results demonstrate a potential pathway for all-optical probing of spin states in van der Waals antiferromagnets, with relevance for spin-sensitive optoelectronic and magneto-optical devices.