Electronic transport in Ba1-xKxBiO3 single crystals

We report measurements of the thermopower and resistivity of two supercondu cting Ba1-xKxBiO3 single crystals with x similar to 0.4 (close to optimal d oping), and analyze these data together with earlier data for K concentrati ons that span the accessible metallic and superconducting phase 0.37<x<0.55 . The thermopower S for temperatures below 120 K exhibits similar behavior to that seen for the cuprates close to optimal doping: the thermopower is p ositive for temperatures just above T-c but decreases with increasing tempe rature. A change of slope appears in the thermopower data at T similar to 1 20-150 K, with an increase in dS/dT above this temperature. We show that al l the data can be accounted for by a two-band model similar to that used by Hashimoto et al. to explain the thermopower of the related superconductor, BaPb0.75Bi0.25O3, and are consistent with the reported persistence of the charge-density-wave gap in the superconducting phase near the metal-semicon ductor transition.