Thermoelectric properties of the Kondo semiconductor: Yb1-xLuxB12

We have measured electrical resistivity rho, thermal conductivity kappa, an d thermopower S of the Kondo semiconductor Yb1-xLuxB12 (0 less than or equa l to x less than or equal to 1). On increasing x to 0.05, both the semicond ucting increase in rho (T) and the enhancement of kappa below 60 K are stro ngly suppressed. A giant negative peak in S(T) for x = 0 at 10 K vanishes a lready at x = 0.01, whereas a broad peak stays at 30 K for x less than or e qual to 0.25 and shifts to 100 K for x greater than or equal to 0.75. These results suggest that the energy gap in YbB12 is filled up by the developme nt of a mid-gap state at the Fermi level with Lu substitution. (C) 2001 Els evier Science B.V. All rights reserved.