Kondo-hole conduction in the la-doped kondo insulator Ce3Bi4Pt3

The resistivity, Hall constant, specific heat, and magnetic susceptibility of the doped Kondo insulator (Ce1-xLax)(3)Bi4Pt3 are studied as a function of temperature and x. Already at x= 0.006, the alloy behaves like a metal, so that the metal-insulator transition in the impurity band must occur at a lower concentration. Our data allow to determine the effective mass m* and the carrier concentration n separately. After a strong initial increase of n(x), the carrier concentration remains nearly constant between x= 0.1 and 0.5. The effective mass in the metallic state initially increases with x and reaches a maximum of m* approximate to 100m(0) at x= 0.3. The scattering time tau as determined from the Drude formula decreases drastically between x= 0.006 and 0.1, has a minimum at about x= 0.1, and then a maximum at x= 0.3. Surprisingly, m*/tau is nearly constant for the entire alloy range for x >= 0.1.