Anomalous thermoelectric transport phenomena from interband electron-phonon scattering

TL;DR

This paper reveals a novel electron-phonon scattering regime in thermoelectric materials where multiple bands at the Fermi level cause unusual transport behaviors, including sign reversal of the Seebeck coefficient and a second peak in power factor.

Contribution

It introduces a new scattering regime caused by interband electron-phonon interactions, providing insights for designing high-performance thermoelectric materials.

Findings

Electrical conductivity decreases with doping in the anomalous regime.

Seebeck coefficient can reverse sign at high doping levels.

Power factor shows an unusual second peak.

Abstract

The Seebeck coefficient and electrical conductivity are two critical quantities to optimize simultaneously in designing thermoelectric materials, and they are determined by the dynamics of carrier scattering. We uncover a new regime where the co-existence at the Fermi level of multiple bands with different effective masses leads to strongly energy-dependent carrier lifetimes due to intrinsic electron-phonon scattering. In this anomalous regime, electrical conductivity decreases with carrier concentration, Seebeck coefficient reverses sign even at high doping, and power factor exhibits an unusual second peak. We discuss the origin and magnitude of this effect using first-principles Boltzmann transport calculations and simplified models. We also identify general design rules for using this paradigm to engineer enhanced performance in thermoelectric materials.