Deciphering the lattice vibrational behaviors of CuInP2S6 by angle-resolved polarized Raman scattering

TL;DR

This study combines polarized Raman spectroscopy and first-principles calculations to analyze the anisotropic lattice vibrations of CuInP2S6, revealing symmetry properties, phase transition behaviors, and providing insights into its ferroelectric mechanisms.

Contribution

It offers a comprehensive experimental and theoretical analysis of lattice dynamics and vibrational symmetries in CuInP2S6, advancing understanding of its ferroelectric properties.

Findings

Identified symmetry assignments and Raman tensors of vibrational modes.

Demonstrated Raman spectroscopy as a probe for phase transitions.

Revealed thickness-dependent polarization suppression.

Abstract

The layered van der Waals (vdW) ferroelectric CuInP2S6 (CIPS) exhibits unique cation hopping-driven phenomena that bring about unconventional properties with intriguing mechanisms and hold promises for advanced applications in nanoelectronics. However, an explicit analysis of its lattice dynamics and vibrational symmetries, pivotal for understanding the material's peculiar ferroelectric and ferroionic behaviors, remains incomplete. Here, we employ angle-resolved polarized Raman spectroscopy in concert with first-principles calculations to systematically unravel the anisotropic lattice vibrations of CIPS single crystals. By analyzing the polarization-dependent Raman intensities, we determine the symmetry assignments and Raman tensors of all major vibrational modes, revealing good agreement with theoretical predictions. Furthermore, we demonstrate the utility of Raman spectroscopy as a sensitive and non-invasive probe for structural and ferroelectric order evolution, by examining temperature-driven phase transitions and thickness-dependent polarization suppression in CIPS. Our findings establish a foundational framework for correlating lattice dynamics with functional properties in CIPS and provide a methodological blueprint for studying other vdW ferroelectrics.