Raman scattering investigation of structural phase transition in compressed EuSn2As2

Abstract

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.