Junction Using Ba_1-xK_xBiO₃ Thin Films

Abstract

We have fabricated a contact junction between an epitaxially grown YBa₂Cu₃O₇₄ thin film and a polycrystalline Ba _{?? x}K_xBiO₃ thin film. This contact junction shows the typical I-V characteristics of quasi-particle tunneling which are observed for junctions consisting of electrodes having different superconducting energy gaps. From the I-V characteristics, the superconducting energy gap, 2Δ, is estimated to be 1.5 meV along the c-axis for YBa₂Cu₃O₇₄ and 3 meV for Ba _{?? x}K_xBiO₃₊ The 2Δ/kTc for the Ba _{?? x}K_xBiO₃ is about 3.5, which is equal to that derived from a boundary Josephson junction. These properties show that the contact boundary between YBa₂Cu₃O₇₄ and Ba _{?? x}K_xBiO₃ works as the tunneling barrier.