Thermoelectric properties of the Kondo semiconductor: Yb1− Lu B12

Abstract We have measured electrical resistivity ρ, thermal conductivity κ, and thermopower S of the Kondo semiconductor Yb1−xLuxB12 (0⩽x⩽1). On increasing x to 0.05, both the semiconducting increase in ρ(T) and the enhancement of κ below 60 K are strongly suppressed. A giant negative peak in S(T) for x=0 at 10 K vanishes already at x=0.01, whereas a broad peak stays at 30 K for x⩽0.25 and shifts to 100 K for x⩾0.75. These results suggest that the energy gap in YbB12 is filled up by the development of a mid-gap state at the Fermi level with Lu substitution.