Unchanged thermopower enhancement at the semiconductor-metal transition in correlated FeSb_2-x Te_x

Substitution of Sb in FeSb₂ by less than 0.5% of Te induces a transition from a correlated semiconductor to an unconventional metal with large effective charge carrier mass m*. Spanning the entire range of the semiconductor-metal crossover, we observed an almost constant enhancement of the measured thermopower compared to that estimated by the classical theory of electron diffusion. Using the latter for a quantitative description one has to employ an enhancement factor of 10-30. Our observations point to the importance of electron-electron correlations in the thermal transport of FeSb₂, and suggest a route to design thermoelectric materials for cryogenic applications.