Magnetoresistance and thermoelectric power of Sr1-xKxBiO3: a second familyof BiO-based superconductors

We have measured the temperature dependence of magnetoresistance and thermo electric power (TEP) for the Sr1-xKxBiO3 superconductor (x = 0.45 - 0.6). T he onset temperature of superconductivity in resistivity measurement is 12. 5 K and the resistivity goes to zero at 10.2 K. The upper critical field (H -c2(0)) and the coherence length (xi (0)) determined by the criterion rho ( H = H-c2) = 0.9 rho (n), where rho (n) is the normal state resistivity, S = 1.96 muV/K estimated to be 5.09 Tesla. and 79.1 Angstrom, respectively. TE P at room temperature hay a small negative value ( S = -1.96 muV/K) and its temperature dependence shows two distinct features. The sign of TEP change s from negative to positive at 210 K. As lowering the temperature, the nega tive slope of TEP (dS/dT) decreases and becomes rather flat at around 160 K , which is a feature noted in other BiO-based superconductors.