Bulk Signatures of Pressure-Induced Band Inversion and Topological Phase Transitions in Pb$_{1-x}$Sn$_x$Se

TL;DR

This study reveals bulk signatures of pressure-induced topological phase transitions in Pb$_{1-x}$Sn$_x$Se through infrared measurements, showing band gap closing and reopening, and changes in carrier density.

Contribution

It provides the first comprehensive bulk optical evidence of pressure-driven topological phase transitions in Pb$_{1-x}$Sn$_x$Se, emphasizing bulk properties over surface effects.

Findings

Band gap closes and reopens under pressure.

Maximum in free carrier spectral weight at transition.

Enhanced density of states near the band gap in the topological phase.

Abstract

The characteristics of topological insulators are manifested in both their surface and bulk properties, but the latter remain to be explored. Here we report bulk signatures of pressure-induced band inversion and topological phase transitions in Pb$_{1-x}$Sn$_x$Se ($x=$0.00, 0.15, and 0.23). The results of infrared measurements as a function of pressure indicate the closing and the reopening of the band gap as well as a maximum in the free carrier spectral weight. The enhanced density of states near the band gap in the topological phase give rise to a steep interband absorption edge. The change of density of states also yields a maximum in the pressure dependence of the Fermi level. Thus our conclusive results provide a consistent picture of pressure-induced topological phase transitions and highlight the bulk origin of the novel properties in topological insulators.