Optical investigation of the thermoelectric topological crystalline insulator Pb0.77Sn0.23Se

Pb0.77Sn0.23Se is a promising thermoelectric alloy 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 Pb0.77Sn0.23Se as a function of temperature. We find clear optical signatures suggesting the band inversion occurs at 160 ±15 K, and use the extended Drude model to accurately determine a T3 /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.

Physical Review B, 90, 235144. (2014)