Proximity effect in bilayer films of YBa2Cu2.7Fe0.3Oy and YBa2Cu3O7−δ

We studied the proximity effect in a series of YBa2Cu2.7Fe0.3Oy/YBa2Cu3O7−δ bilayer film with varying YBa2Cu3O7−δ thickness. In a bilayer of isolated YBCO islands, a Tc of 72 K was observed, much higher than Tc of 32 K of the YBa2Cu2.7Fe0.3Oy film. Tc and Jc of thicker bilayers of continuous YBa2Cu3O7−δ films were found to decrease with decreasing YBCO thickness. This behavior of Tc and Jc can be explained by the Deutscher de Gennes theory for the proximity effect, provided one models the film as a series of grains whose lateral dimensions scale with the average film thickness.