Robust phonon engineering and symmetry-selective lattice dynamics in CrSBr$_{1-x}$Cl$_{x}$

TL;DR

This study explores how atomic substitution of Cl for Br in CrSBr alters lattice vibrations and symmetry, using Raman spectroscopy and first-principles calculations to reveal systematic phonon shifts, symmetry lowering, and electron-phonon interactions.

Contribution

It provides a detailed analysis of phonon evolution and symmetry changes in CrSBr$_{1-x}$Cl$_{x}$ due to Cl substitution, combining experimental and theoretical approaches.

Findings

Cl substitution shifts phonon modes systematically

Symmetry lowering activates new Raman features

Electron-phonon coupling remains robust with Cl doping

Abstract

Atomic substitution provides a controlled route to engineer lattice dynamics in low-symmetry two-dimensional materials. Here, by combining polarization-resolved Raman spectroscopy and first-principles calculations, we investigate the evolution of phonon characteristics in CrSBr$_{1-x}$Cl$_{x}$ ($0 \leq x \leq \sim 0.5$) upon partial substitution of Br with Cl atoms. Progressive Cl substitution of Br induces systematic shifts of parent CrSBr out-of-plane $A_\textrm{g}$ phonon modes and activates additional Raman features. These features persist across different polarization configurations and excitation energies, reflecting substitution-induced symmetry lowering and local lattice perturbations. Explicit supercell phonon calculations combined with Raman $\Gamma$-density-of-states simulations identify these features as symmetry-lowered descendants of parent modes arising from alloy disorder. Complementary strain-dependent calculations reveal that anisotropic lattice compression plays a key role in renormalizing Cr-S dominated phonons. Under near-resonant excitation, stimulated Raman scattering-like amplification remains observable with increasing Cl content, highlighting the resilience of anisotropic electron-phonon coupling in this system.