Upper critical field in Ba _{1 − <i>x</i>} K _<i>x</i> BiO ₃ : Magnetotransport <i>vs.</i> magnetotunneling

Abstract

Elastic tunneling is used as a powerful direct tool to determine the upper\ncritical field $H_{c2}(T)$ in the high-$T_c$ oxide Ba$_{1-x}$K$_x$BiO$_3$. The\ntemperature dependence of $H_{c2}$ inferred from the tunneling follows the\nWerthamer-Helfand-Hohenberg prediction for type-II superconductors. A\ncomparison will be made with resistively determined critical field data.\n