Critical current behavior of Ag-coated YBa2Cu3O7-x thin films

The authors studied the behavior of high-quality Ba₂Cu ₃O_7-x (YBCO) thin films with Ag overlayers. The authors chose to study Ag in detail because of its widespread use as contact metallization and because of their earlier studies of proximity effects in YBCO. The details of transport critical current measurements are presented. It is shown that the Ag coatings can reduce normal state resistance while not degrading the critical current density. The key technological result is that the various thicknesses of Ag that were used did not reduce J_c or J_c(H). Critical current densities in excess of 10⁶ A/cm² have been achieved at temperatures greater than 76 K. An unusual effect was seen in J_c(H) when the field was oriented perpendicular to the c axis of the film. The J_c at 1 T was higher in samples with 10-nm coatings of Ag than in similar uncoated samples. It was also shown that the composite resistance of Ag-YBCO bilayers can be much lower than the resistance of uncoated YBCO