UPPER CRITICAL-FIELD IN THE BA1-XKXBIO3 SUPERCONDUCTOR

We have performed simultaneously magnetotransport and magnetotunneling experiments on Ba1-xKxBiO3 single crystals (T-c similar to 23 K) in m agnetic fields up to 30 Tesla (similar to H-c2(O)) to determine the up per critical field H-c2. A completely different modulus and temperatur e dependence of 'the critical fields' are obtained by the dissipative method (magnetoresistance) and the non-dissipative one (tunneling). Wh ile H-c2(T) from tunneling follows the BCS prediction, the magnetotran sport data show rather a melting line in the field-versus-temperature H - T phase diagram of this 3D - superconductor. One can speculate tha t the same situation holds in high-T-c, cuprates.