c-axis tunneling in YBa2Cu3O7-δ/PrBa2Cu3O7-δ superlattices

In this work we report c-axis conductance measurements done on a superlattice based on a stack of two layers of YBa2CU3O7-delta and Seven layers of PrBa2Cu3O7-delta (2.:7). We find that these quasi-two-dimensional structures show no clear superconducting coupling along the c axis. Instead, we observe tunneling with a gap of Delta(c) = 5.0 +/- 0.5 meV for the direction perpendicular to the superconducting planes. The conductance spectrum show well defined quasiperiodic structures which are attributed to the superlattice structure. From this data we deduce a low-temperature c-axis coherence length of xi(c) = 0.24 +/- 0.03 nm.