Sharp Raman Anomalies and Broken Adiabaticity at a Pressure Induced Transition from Band to Topological Insulator in Sb2Se3

TL;DR

This study reveals vibrational anomalies in Raman spectra indicating a pressure-induced electronic topological transition in Sb2Se3, highlighting nonadiabatic phonon-electron interactions as key signatures of topological phase change.

Contribution

It demonstrates that nonadiabatic phonon renormalization serves as a measurable bulk signature of the electronic topological transition in Sb2Se3, advancing understanding of topological insulator development.

Findings

Raman spectra show phonon softening and linewidth anomalies at the ETT

First-principles calculations confirm the electronic transition and parity reversal

Breakdown of adiabatic approximation due to phonon-electron coupling

Abstract

The nontrivial electronic topology of a topological insulator is thus far known to display signatures in a robust metallic state at the surface. Here, we establish vibrational anomalies in Raman spectra of the bulk that signify changes in electronic topology: an E2 g phonon softens unusually and its linewidth exhibits an asymmetric peak at the pressure induced electronic topological transition (ETT) in Sb2Se3 crystal. Our first-principles calculations confirm the electronic transition from band to topological insulating state with reversal of parity of electronic bands passing through a metallic state at the ETT, but do not capture the phonon anomalies which involve breakdown of adiabatic approximation due to strongly coupled dynamics of phonons and electrons. Treating this within a four-band model of topological insulators, we elucidate how nonadiabatic renormalization of phonons constitutes readily measurable bulk signatures of an ETT, which will facilitate efforts to develop topological insulators by modifying a band insulator.