Interface-engineered Josephson junctions optimized for high JC

High-temperature superconducting interface-engineered junctions were fabricated using YBa₂Cu₃O_7-δ on LaAlO₃ (LAO) and sapphire substrates. We report on the improvements in the electrical characteristics by junction narrowing. Originally, the 2-μm-wide junctions had high critical current densities of 1.2 × 10⁶ 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