Layer breathing Raman mode in two-dimensional van der Waals material $\mathrm{Cr_2Ge_2Te_6}$

TL;DR

This paper reports the observation of the layer breathing mode in few-layer Cr2Ge2Te6 using Raman spectroscopy, revealing insights into interlayer coupling and lattice dynamics in 2D magnetic materials.

Contribution

It introduces the detection and analysis of the layer breathing mode in Cr2Ge2Te6, providing quantitative measures of interlayer forces and understanding of lattice symmetry.

Findings

Layer breathing mode observed in few-layer Cr2Ge2Te6.

LBM frequency softens with increasing layer number.

Interlayer force constant quantified using the Linear Chain Model.

Abstract

Two-dimensional (2D) van der Waals (vdW) magnetic materials have emerged as key materials for next-generation magneto-electric and spintronic devices, where understanding the relationship between layer number, lattice dynamics, and magnetic interactions is very important. In this work, we report the observation of the layer breathing mode (LBM) in few-layer $\mathrm{Cr_2Ge_2Te_6}$, a ferromagnetic semiconductor with thickness dependent electronic, magnetic and optical properties, using Raman spectroscopy, which serves as a direct fingerprint of interlayer coupling and lattice symmetry. Group-theoretical symmetry analysis confirms that the CGT falls under the non-polar category of layered material. The evolution of the LBM-frequency with increasing layer number (N) reveals a distinct softening trend, characteristic of weakening restoring forces in thicker flakes. By fitting the experimental Raman data using the Linear Chain Model (LCM), we quantitatively extract the interlayer force constant ($\mathrm{K_c}$), providing a measure of the vdW coupling strength between layers.