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

Abstract

Low‐leakage, thin‐film planar tunnel junctions made of Y₁Ba₂Cu₃O_7−x/ native barrier/Pb were fabricated. The Y₁Ba₂Cu₃O_7−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 T_c of Pb, the development of a supercurrent at zero bias and associated hysteretic subgap structure, with a typical I_cR ∼0.5 mV. Josephson‐like behavior occurred in response to applied magnetic field and microwaves.