Unchanged thermopower enhancement at the semiconductor-metal transition   in correlated FeSb$_{2-x}$Te$_x$
  Substitution of Sb in FeSb$_2$ 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 FeSb$_2$, and suggest a route to design thermoelectric materials for cryogenic applications. 
P. Sun, M. S{\o}ndergaard, Y. Sun, S. Johnsen, B.B. Iversen, and F.   Steglich
cond-mat.mtrl-sci