Optical investigation of thermoelectric topological crystalline insulator Pb$_{0.77}$Sn$_{0.23}$Se

TL;DR

This study investigates the temperature-dependent optical properties of the thermoelectric topological crystalline insulator Pb$_{0.77}$Sn$_{0.23}$Se, revealing a band inversion at around 160 K and analyzing carrier dynamics, with implications for thermoelectric performance.

Contribution

It provides the first optical evidence of band inversion in Pb$_{0.77}$Sn$_{0.23}$Se and examines how this affects carrier scattering and thermoelectric properties.

Findings

Optical evidence of band inversion at approximately 160 K.

Bulk carrier lifetime follows a T^{3/2} dependence due to electron-acoustic phonon scattering.

No clear signatures of topological surface states due to high bulk doping.

Abstract

Pb$_{0.77}$Sn$_{0.23}$Se is a novel alloy of two promising thermoelectric materials PbSe and SnSe that exhibits a temperature dependent band inversion below 300 K. Recent work has shown that this band inversion also coincides with a trivial to nontrivial topological phase transition. To understand how the properties critical to thermoelectric efficiency are affected by the band inversion, we measured the broadband optical response of Pb$_{0.77}$Sn$_{0.23}$Se as a function of temperature. We find clear optical evidence of the band inversion at $160\pm15$ K, and use the extended Drude model to accurately determine a $T^{3/2}$ dependence of the bulk carrier lifetime, associated with electron-acoustic phonon scattering. Due to the high bulk carrier doping level, no discriminating signatures of the topological surface states are found, although their presence cannot be excluded from our data.