Polarized Raman Spectra of Layered CrPS₄

Chromium thiophosphate (CrPS₄), a monoclinic crystal of C₂ space group, is a ternary layered semiconductor with an optical bandgap of 1.4 eV and exhibits antiferromagnetism below 36 K. Despite its potential in optoelectronic and magnetic applications, its lattice vibrations have not been studied. In this work, we performed a polarized Raman spectroscopy study of bulk CrPS₄. High quality crystals grown by the chemical vapor transport method were mechanically exfoliated into thin crystals for cleavage-plane excitation and mechanically polished for edge-plane excitation. Polarized Raman spectra were obtained in parallel and cross configurations, where the polarization of the Raman signal was parallel and perpendicular to that of the excitation beam, respectively. Among 33 Raman active modes (16 A and 17 B) at the Brillouin zone center, 14 (8) peaks observed in the parallel (cross) configuration were assigned as A (B) modes. To determine the Raman tensor values, the angular dependence of A and B modes were systematically investigated by rotating crystals with respect to the excitation polarization. The results can be used in determining crystallographic orientation unequivocally.