Thermoelectric properties of the Kondo semiconductor: Yb1−x LuxB12

Abstract We have measured electrical resistivity ρ , thermal conductivity κ , and thermopower S of the Kondo semiconductor Yb 1− x Lu x B 12 (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 YbB 12 is filled up by the development of a mid-gap state at the Fermi level with Lu substitution.