Heavy fermion metal–Kondo insulator transition inFeSi1−xAlx

Doping the Kondo insulator FeSi with Al at the Si site introduces carriers and eventually yields metallic conduction. The lattice constant, thermoelectric effect, Hall effect, electrical conductivity, magnetic susceptibility, specific heat, and magnetoresistance have been measured over the $0<x<\mathrm{}0.08\mathrm{}$ range of Al concentration. All of these quantities show a systematic variation with x including a metal-insulator transition for carrier densities between $2.2\times {10}^{20}$ and $4.4\times {10}^{20}\hspace{0.5em}{\mathrm{cm}}^{-3}.$ A detailed analysis of the transport and thermodynamic properties reveal a metal-insulator transition closely resembling that of the classic semiconductors (Si:P, Si:B, and Ge:Sb) with one important exception: a substantially enhanced carrier mass.