Brightened Optical Transition Hinting to Strong Spin-Lattice Coupling in a Layered Antiferromagnet

Two-dimensional (2D) van der Waals magnets show strong interconnection between their electrical, magnetic, and structural properties. Here, the emergence of a luminescent transition is revealed upon crossing the Néel transition temperature of CrPS₄, a layered antiferromagnetic semiconductor. This luminescent transition occurs above the lowest absorption level. The optical transitions are attributed to excited states of the t_2g orbitals of the Cr³⁺ ions, which are influenced by the distortion of the octahedral crystal field. Specifically, the vicinity of the Néel temperature, the distortion switches from an anti-polar to a polar arrangement, thereby not only promoting an additional luminescent pathway but also significantly strengthening the static dipole moment detected by a marked enhancement in the intensity of the second harmonic generation. These results strongly encourage further investigation into the multiferroic properties and potential coupling mechanisms in CrPS₄.