Interface-engineered junctions with YbBaCuO as the counter-electrode

The electric properties of interface-engineered junctions with YbBa₂Cu₃O₇ as the counter-electrode were investigated. The junctions exhibited excellent Josephson characteristics with the critical current density (J_c) ranging from 10² A/cm² to more than 10⁶ A/cm², and the normal resistance (R_n) ranging from 10^-6 Ωcm² to 10^-9 Ωcm². The R_n values varied approximately in accordance with J_c^-p, where p was close to 0.25 for low-J_c junctions and increased gradually up to 0.75 for high-J_c junctions. The junctions with R_n exceeding 10^-7 Ωcm² exhibited dI/dV profiles peculiar to tunneling processes via localized states. The dI/dV profiles of the junctions with lower R_n were characterized by reproducible fine structures below 15 mV, probably due to multiple Andreev reflections. These results indicate that the crossover from the tunneling regime to metallic weak-links takes place in these junctions depending on the process conditions.