Phonon thermal Hall effect in charge-compensated topological insulators

TL;DR

This study reveals a significant low-temperature phonon-dominated thermal Hall effect in charge-compensated topological insulators, suggesting a phononic mechanism possibly involving skew scattering on impurities.

Contribution

It provides the first systematic experimental evidence of a phononic thermal Hall effect in topological insulators and supports a skew scattering theoretical model.

Findings

Large low-temperature thermal Hall effect observed

Thermal conductivity is phonon-dominated in all samples

Thermal Hall ratio supports skew scattering mechanism

Abstract

From a systematic study of thermal and charge transport in various single crystals of compensated topological insulators we identify the evolution of a large low-temperature thermal Hall effect as a characteristic common feature. In order to separate phononic and electronic contributions in the measured longitudinal and transverse thermal conductivity, the electronic contributions are estimated from corresponding electrical resisivity and Hall effect measurements on the same samples by using the Wiedemann-Franz law. As may be expected for charge-compensated topological insulators the longitudinal thermal conductivity is phonon-dominated in all samples. However, we also find a pronounced field-linear thermal Hall effect that becomes most pronounced in the low-temperature range, where all samples are good electrical insulators. This indicates an underlying phononic mechanism of the thermal Hall effect and in this respect the topological insulators resemble other, mainly ionic, insulators, which have been reported to show a phonon-induced thermal Hall effect, but its underlying phononic mechanism remains to be identified. Our observation of a comparable thermal Hall ratio in topological insulators supports a theoretical scenario that explains a thermal Hall effect through skew scattering on charged impurities.