PROXIMITY EFFECT IN BILAYER FILMS OF YBA2CU2.7FE0.3OY AND YBA2CU3O7-DELTA

We studied the proximity effect in a series of YBa2Cu2.7Fe0.3Oy/YBa2Cu 3O7-delta bilayer film with varying YBa2Cu3O7-delta thickness, In a bi layer of isolated YBCO islands, a T-c of 72 K was observed, much highe r than T-c of 32 K of the YBa2Cu2.7Fe0.3Oy film. T-c and J(c) of thick er bilayers of continuous YBa2Cu3O7-delta films were found to decrease with decreasing YBCO thickness. This behavior of T-c and J(c) 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 dimen sions scale with the average film thickness. (C) 1998 American Institu te of Physics. [S0003-6951(98)02914-3].