LOW-TEMPERATURE TRANSPORT, THERMODYNAMIC, AND OPTICAL-PROPERTIES OF FESI

We present a comprehensive series of electrical transport (conductivit y, magnetoresistance, and Hall effect), thermodynamic (specific heat, magnetic susceptibility, and magnetization), and optical (reflectivity ) measurements in varying temperature ranges between 0.05 and 330 K on high-quality FeSi single crystals grown by vapor transport. The entir e set of data can consistently be described with the usual relations f or a (compensated n type) semiconductor if an unconventional band stru cture is assumed. Compared to the results of mean-held band-structure calculations, the height of the peaks in the total density of states a round the energy gap is considerably enhanced, implying enhanced effec tive masses. Most likely correlation effects are the source of these f eatures. At very low temperatures we encounter metallic behavior. A lo w concentration of correlated itinerant charge carriers coexists with interacting magnetic moments.