Resonant Charge Relaxation as a Likely Source of the Enhanced Thermopower in FeSi

TL;DR

This study suggests that resonant charge scattering at magnetic crossover points is a key factor behind the unusually high thermopower observed in FeSi, a correlated semiconductor.

Contribution

It introduces the idea that resonant charge relaxation explains the enhanced thermopower in FeSi, supported by transport measurements near the magnetic crossover.

Findings

Large maximum in Nernst coefficient at 70 K

Hall mobility drops below 1 cm^2/Vs at the same temperature

Resistivity hump and sign change in magnetoresistance

Abstract

The enhanced thermopower of the correlated semiconductor FeSi is found to be robust against the sign of the relevant charge carriers. At $T$\,$\approx$\,70 K, the position of both the high-temperature shoulder of the thermopower peak and the nonmagnetic-enhanced paramagnetic crossover, the Nernst coefficient $\nu$ assumes a large maximum and the Hall mobility $\mu _H$ diminishes to below 1 cm$^2$/Vs. These cause the dimension-less ratio $\nu$/$\mu_H$ $-$ a measure of the energy dispersion of the charge scattering time $\tau(\epsilon)$ $-$ to exceed that of classical metals and semiconductors by two orders of magnitude. Concomitantly, the resistivity exhibits a hump and the magnetoresistance changes its sign. Our observations hint at a resonant scattering of the charge carriers at the magnetic crossover, imposing strong constraints on the microscopic interpretation of the robust thermopower enhancement in FeSi.