Systematic investigation of ramp edge junction using Ca-doped and Ga-dopedPBCO barrier

We have investigated systematically the characteristics of ramp edge juncti ons with Ca- and Ga-doped PBCO barriers. The localized state density g and/ or the volume of the state nu in the barriers are increased by Ca-doping an d decreased by Ga-doping. Ca-doping reduces the IcRn products, and Ga-dopin g enhances the IcRn products, though the dominant transport mechanisms are direct tnnneling for the junctions having IcRn greater than 1mV. The change in the IcRn products can be interpreted in terms of the proximity effect a t the interface states formed by hybridization between the localized states in the barrier and conduction electron states of electrodes. The ideal sup erconductor-insulator interface at the junction interfaces is required to e nhance IcRn products.