Proximity effect in high-T_c oxide superconductors

The proximity effect in SNS (superconductor-normal conductor-superconductor) junctions composed of the oxides with isomorphic crystal structures is theoretically studied by using a simple model in which the S and N layers have similar electronic structures, and the superconducting pairing interaction works even in the N layer. The proximity effect is enhanced by the pairing interaction and the superconducting pair amplitude is connected between the S layers through the thick N layer which is primarily not superconductive due to a small number of holes. The proximity effects is almost unaffected by elastic impurity scatterings at low temperatures.