Magnetotunneling and magnetic pair-breaking in superconducting Ba1-xKxBiO3

The gapless superconductivity theory for dirty superconductors has been used to interpret the tunneling measurements on the strongly type-II high-T-c oxide-superconductor Ba1-xKxBiO3 in high magnetic fields up to 30 T. This theory describes the tunneling curves at all temperatures below T-c not only near the upper critical field H-c2 but in a wide range of magnetic fields H > 0.5H(c2), yielding an estimation of the pair-breaking parameter alpha. This allows us to determine the temperature dependence of the upper critical field H-c2(T) which is in agreement with the predictions of the classical Werthamer-Helfand-Hohenberg theory. Our results are comparable with H-c2 data directly obtained from the tunneling experiment. (C) 2000 Elsevier Science B.V. All rights reserved.