The coupling between the superconducting planes of YBa2Cu3O7- S/PrBa2Cu3O7-
delta superlattices has been measured by c-axis transport. We show that onl
y by changing the thickness of the superconducting YBa2Cu3O7-delta layers,
it is possible to switch between quasi-particle and Josephson tunneling. Fr
om our data we deduce a low-temperature c-axis coherence length of xi(c) =
0.27 nm. (C) 2000 Elsevier Science B.V. All rights reserved.