  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.
