Observations of quasi-particle tunneling and Josephson behavior in Y1Ba2Cu3O7−<i>x</i>/ native barrier/Pb thin-film junctions

Abstract

Low-leakage, thin-film planar tunnel junctions made of Y1Ba2Cu3O7−x/ native barrier/Pb were fabricated. The Y1Ba2Cu3O7−x films were prepared by in situ molecular beam epitaxy aided with an activated oxygen source. The as-grown, smooth superconducting perovskite film surface exhibits quasi-particle tunneling characteristics very similar to the etched bulk single-crystal data. The results in agreement are a linear dependence of the normal-state conductance on voltage, a gap-like structure at ∼20 mV, asymmetric modulations up to 50 mV, and a finite zero-bias conductance at low temperature. Junctions of lower resistance show, at temperatures below Tc of Pb, the development of a supercurrent at zero bias and associated hysteretic subgap structure, with a typical IcR ∼0.5 mV. Josephson-like behavior occurred in response to applied magnetic field and microwaves.