The effects of step angle on step edge Josephson junctions on MgO

Abstract

We have fabricated step edge junctions using MgO substrates and YBCO thin films. By varying the angle of the step edge over a range of angles up to 45/spl deg/, we have obtained 3 distinct step edge morphologies: a deep trench junction, a double junction and a single junction. We found that only the step angle and morphology affected the critical current density (I/sub c/) and that the film thickness-to-step height ratio had no effect over the range 0.2-1.1. Noise measurements indicated that the single junction steps had the lowest level of critical current fluctuations and the highest values of dynamic resistance. We have also studied the variation of I/sub c/ with temperature and found it follows the Ambergaokar-Baratoff model with a lower zero energy gap. We use this information to confirm that the junction parameters are affected by the c-axis tilt and the in-plane orientations proposed by others and consider the transport mechanisms across the junction.