LAUSR

We present simultaneous suppression of FeSb2 thermal conductivity and electronic correlations in Fe1−xRuxSb2 (0 ≤ x ≤ 0.6) single crystal alloys. Small energy gap Δ 1 in Kondo-insulator-like semiconductor FeSb2 associated with impurity in-gap state increases whereas the intrinsic bandgap Δ 2 decreases upon Ru substitution on Fe atomic site. Thermopower is suppressed along with the intrinsic bandgap and with the thermal conductivity. The more delocalized 4d character of atomic orbital of Ru brings suppression of electronic correlations, but also an increase in impurity density which reduces phonon mean free path and surface scattering length. Our results indicate a range of Ru doping x where nanostructuring could be used to suppress thermal conductivity further, potentially toward the amorphous limit.