Superconductor-insulator-superconductor tunneling in Ba1−<i>x</i>K<i>x</i>BiO3 grain boundaries

Abstract

We have prepared single grain boundaries of the superconductor Ba1−xKxBiO3 by growing epitaxial thin films of this compound on SrTiO3 bicrystal substrates. The four-terminal current-voltage characteristics of the grain boundaries showed clear superconductor- insulator-superconductor (SIS) tunneling behavior. The leakage at zero bias was smaller than 0.3% at 4.2 K. The differential conductance displayed sharp symmetric peaks at 2Δ close to 6.5 mV. At higher bias, an increase in conductance proportional to V2 was observed. The temperature dependence of the conductance was found to be in qualitative accord with conventional SIS theory.