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 ${\mathrm{cm}}^2$/V s. These cause the dimensionless ratio $\nu /{\mu }_H$—a measure of the energy dispersion of the charge scattering time $\tau \left(\epsilon \right)$—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.

• Received 25 July 2014
• Revised 8 December 2014

DOI:https://doi.org/10.1103/PhysRevB.90.245146