Thermopower of correlated semiconductors : application to FeAs2 and FeSb2

TL;DR

This study examines how electronic correlations influence thermoelectric properties in semiconductors, finding that correlations do not inherently enhance thermopower and highlighting the importance of many-body effects for accurate modeling of FeSb2.

Contribution

It provides a detailed analysis of correlation effects on thermopower in semiconductors, applying advanced many-body techniques to FeAs2 and FeSb2.

Findings

Correlation effects do not inherently increase Seebeck coefficient.

Density functional theory accurately describes FeAs2's thermopower.

GW approximation captures FeSb2's insulating ground state.

Abstract

We investigate the effect of electronic correlations onto the thermoelectricity of semi-conductors and insulators. Appealing to model considerations, we study various many-body renormalizations that enter the thermoelectric response. We find that, contrary to the case of correlated metals, correlation effects do not per se enhance the Seebeck coefficient or the figure of merit, for the former of which we give an upper bound in the limit of vanishing vertex corrections. For two materials of current interest, FeAs2 and FeSb2, we compute the electronic structure and thermopower. We find FeAs2 to be well described within density functional theory, and the therefrom deduced Seebeck coefficient to be in quantitative agreement with experiment. The capturing of the insulating ground state of FeSb2, however, requires the inclusion of many-body effects, in which we succeed by applying the GW approximation. Yet, while we get qualitative agreement for the thermopower of FeSb2 at intermediate temperatures, the tremendously large Seebeck coefficient at low temperatures is found to violate our upper bound, suggesting the presence of decisive (e.g. phonon mediated) vertex corrections.