Upper critical field in {Ba${}_{1-x}$K${}_x$BiO${}_3$}: magnetotransport versus magnetotunneling

Abstract

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

4 pages incl. 5 figures