THE EFFECT OF BARRIER THICKNESS AND INTERFACE RESISTANCE UPON THE CRITICAL CURRENTS OF YBA2CU3O7-DELTA NOBLE-METAL CONVENTIONAL SUPERCONDUCTOR JUNCTIONS

We report a study of the critical current I(c) of YBa2Cu3O7-delta (YBC O)/noble metal/conventional superconductor structures with noble-metal thicknesses in the range 20 nm to 1 mum and resistance-area products R(n)A between 10(-9) OMEGA cm2 and 10(-5) OMEGA cm2. Good agreement wa s found between the temperature dependence of I(c) and the predictions of a simple proximity-effect theory which assumed that there was no d egraded layer between the YBCO and the noble metal. The magnitude of I (c), corrected for the sample temperature and noble-metal thickness us ing the theory, was found to scale with R(n)-1. These observations are shown to be consistent with a model in which the YBCO/noble metal int erface is highly nonuniform with the total area of low-resistance cont act making up only a small fraction of the total junction area. This e xplains the large interface resistivities observed in the YBCO/noble m etal system.