Investigation of YBCO step-edge Josephson junctions

The authors report on the superconducting transport properties of YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) Josephson junctions fabricated by pulsed laser deposition on steep steps in epitaxial substrates. The steps were prepared by Ar-ion milling. The YBCO thin films were patterned either by Ar-ion milling or an inhibit process. The current-voltage characteristics of step-edge junctions (SEJs) fit approximately the resistively shunted-junction (Stewart-McCumber) model up to temperatures of 85 K. The temperature dependence of the characteristic voltage can be explained by a superconductor-normal-superconductor (SNS)type model. Simulations of Shapiro steps were performed. The simulations, the form of the I(V) curves, the I/sub c/(H) curves. and the DC superconducting quantum interference device (SQUID) quantization properties all suggest that a SEJ consists of two weak links in series formed by the grain boundaries at the lower and upper edges of the steps. This conclusion is in good agreement with HREM results, which show that the upper and lower grain boundaries at the step edge are different. Each of these weak links is a parallel array of Josephson junctions with different current densities.<>