Polarized Raman Spectra and Complex Raman Tensors of Antiferromagnetic Semiconductor CrPS4

TL;DR

This study systematically analyzes the polarized Raman spectra of CrPS4, revealing detailed symmetry and tensor properties of its lattice vibrations, which aids in understanding its magnetic and optical characteristics.

Contribution

It provides the first comprehensive polarized Raman analysis of CrPS4, including determination of complex Raman tensors for key vibrational modes.

Findings

Identified 19 Raman-active modes in CrPS4.

Determined complex Raman tensors for 7 major A modes.

Established methods for crystallographic orientation determination.

Abstract

Chromium thiophosphate (CrPS4), a monoclinic crystal of C_2^3 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, the symmetry of its lattice vibrations has not been systematically studied. In this work, we performed a polarized Raman spectroscopy of bulk CrPS4 using three different excitation wavelengths of 457, 514, and 633 nm. High-quality crystals grown by the chemical vapor transport method were mechanically exfoliated or polished to expose three orthogonal crystallographic facets. Polarized Raman spectra were obtained in parallel and cross configurations by rotating samples about the surface normal to each of the facets. Among 33 Raman active modes (16 A and 17 B) at the Brillouin zone center, 19 (8) peaks observed in the parallel (cross) configuration were assigned as A (B) modes. Complex-valued Raman tensors were determined for 7 major A modes using the angle-dependent Raman spectra of the three facets. The results can also be used in determining the crystallographic orientations of CrPS4 unequivocally.