Absence of proximity coupling in ultra-thin c-axis oriented YBa2Cu3O7 - Au bilayers

We have measured the mutual inductance signal of the superconducting transition in ultra-thin YBa 2 Cu 3 O 7 - Au bilayers. The samples consist of d S = 50 A of c -axis oriented YBa 2 Cu 3 O 7 , capped with initially d N = 50 A of Au. As d N is increased on each sample, no decrease in T c is observed, to within our experimental resolution. These results set an upper limit of ≤ 15 A on the proximity coupling range of YBa 2 Cu 3 O 7 , through Au.