Spin-flip optical excitations in van der Waals antiferromagnet CrPS${}_4$

We investigate the near-infrared optical response of the semiconducting van der Waals antiferromagnet CrPS${}_4$ 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 CrPS${}_4$. From the magnetic field evolution of the optical transition, we extract key magnetic parameters, including the spin-flop ($\approx 0.9$~T) and spin-saturation ($\approx 8$~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.