Ba(1-x)K(x)BiO3 thin film Josephson tunnel junctions

We have fabricated sandwich-type Josephson tunnel junction devices from Ba1-xKxBiO3 electrodes and KNbO3 insulating barriers. Near ideal superconductor-insulator-superconductor tunnel junction pp structure was seen in high resistance devices at 4.2 K. Lower resistance devices with similar gap structure but much higher subgap leakage were hysteretic with switching voltages up to 5 mV. Hysteresis and well-defined gap structure persisted past 12 K. Magnetic field modulation of the zero-bias pair current showed Fraunhofer-like behavior with almost complete quenching at the nodes.