Thermoelectricity in correlated narrow-gap semiconductors

TL;DR

This paper reviews the effects of many-body interactions on thermoelectric properties in correlated narrow-gap semiconductors, highlighting their unusual temperature-dependent behavior and proposing a classification of paramagnetic insulators.

Contribution

It provides a comprehensive review of microscopic origins and impacts of many-body effects on thermoelectricity, introduces a classification scheme, and discusses new insights into correlated intermetallics and their thermoelectric potential.

Findings

FeSi identified as an orbital-selective Kondo insulator.

Spectral weight transfers over large energies are linked to the insulator-metal crossover.

Correlated effects influence transport properties and thermoelectric performance.

Abstract

We review many-body effects, their microscopic origin, as well as their impact onto thermoelectricity in correlated narrow-gap semiconductors. Members of this class---such as FeSi and FeSb$_2$---display an unusual temperature dependence in various observables: insulating with large thermopowers at low temperatures, they turn bad metals at temperatures much smaller than the size of their gaps. This insulator-to-metal crossover is accompanied by spectral weight-transfers over large energies in the optical conductivity and by a gradual transition from activated to Curie-Weiss-like behaviour in the magnetic susceptibility. We show a retrospective of the understanding of these phenomena, discuss the relation to heavy-fermion Kondo insulators---such as Ce$_3$Bi$_4$Pt$_3$ for which we present new results---and propose a general classification of paramagnetic insulators. From the latter FeSi emerges as an orbital-selective Kondo insulator. Focussing on intermetallics such as silicides, antimonides, skutterudites, and Heusler compounds we showcase successes and challenges for the realistic simulation of transport properties in the presence of electronic correlations. Further, we advert to new avenues in which electronic correlations may contribute to the improvement of thermoelectric performance.