Highly Dispersive Electron Relaxation and Colossal Thermoelectricity in the Correlated Semiconductor FeSb$_2$

TL;DR

FeSb$_2$ exhibits colossal thermoelectric power, Nernst coefficient, and magnetoresistance below 30 K, driven by highly dispersive electron relaxation due to electron-electron correlations, unlike the reference compound FeAs$_2$.

Contribution

This study reveals that the unusual thermoelectric and magnetoresistive properties of FeSb$_2$ are caused by highly dispersive electron relaxation times stemming from electron-electron correlations.

Findings

FeSb$_2$ shows colossal thermoelectric power below 30 K.

The Nernst coefficient and magnetoresistance are significantly enhanced in FeSb$_2$.

FeAs$_2$ does not exhibit similar enhancements, highlighting the role of electron correlations in FeSb$_2$.

Abstract

We show that the colossal thermoelectric power, $S(T)$, observed in the correlated semiconductor FeSb$_2$ below 30\,K is accompanied by a huge Nernst coefficient $\nu(T)$ and magnetoresistance MR$(T)$. Markedly, the latter two quantities are enhanced in a strikingly similar manner. While in the same temperature range, $S(T)$ of the reference compound FeAs$_2$, which has a seven-times larger energy gap, amounts to nearly half of that of FeSb$_2$, its $\nu(T)$ and MR$(T)$ are intrinsically different to FeSb$_2$: they are smaller by two orders of magnitude and have no common features. With the charge transport of FeAs$_2$ successfully captured by the density functional theory, we emphasize a significantly dispersive electron-relaxation time $\tau(\epsilon_k)$ due to electron-electron correlations to be at the heart of the peculiar thermoelectricity and magnetoresistance of FeSb$_2$.