Raman scattering investigation of structural phase transition in compressed EuSn₂As₂ Available to Purchase

The layered EuSn₂As₂ crystal has been proved to be an intrinsic magnetic topological insulator with Bi₂Te₃-type rhombohedral structure at ambient conditions and undergoes a structural phase transition under pressure. Here, we report an experimental lattice vibration study of EuSn₂As₂ up to 30.5 GPa by in situ Raman scattering measurements. Four Raman-active modes (2A₁g + 2Eg) at ambient pressure are observed experimentally and identified by first-principles calculations. Upon compression, the Eg² and A₁g² modes merge together at 12.45 GPa, meanwhile the frequencies, intensities, and linewidths of all Raman modes show discontinuous changes, exhibiting a structural phase transition. No Raman-active modes are observed above 21.5 GPa, indicating the new high-pressure metallic phase is completely achieved. The evolution of all observed modes under pressure is also discussed with a two-stage reconstruction mechanism proposed recently by ab initio calculations and XRD measurements. These results provide a basic information about the lattice dynamics and expand our understandings on the structural evolution in layered magnetic topological insulators under high pressure.