Interface-engineered Josephson junctions optimized for high J/sub C/

High-temperature superconducting interface-engineered junctions were fabricated using YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// on LaAlO/sub 3/ (LAO) and sapphire substrates. We report on the improvements in the electrical characteristics by junction narrowing. Originally, the 2-/spl mu/m-wide junctions had high critical current densities of 1.2 /spl times/ 10/sup 6/ A/cm at 4.0 K and showed wide junction effects. Narrowing the junctions to below a micrometer reduced the wide junction effect over a large range of temperatures and the junctions had characteristic voltages of 5.16 mV at 4.0 K. The magnetic-field modulation of the critical current was also more ideal after narrowing. Furthermore, we show that interface engineered junctions on sapphire substrates have similar characteristics to those on LAO.