Long range proximity effect in High Tc Josephson NanoJunctions : a quantitative study.

Proximity effect (PE) between a superconductor (S) and a normal metal (N) has been a powerful tool to study conventional superconductors. In High Tc (HTc) compounds, low quality interfaces and poor Fermi wave-vector match with most of common metals usually considerably reduce the proximity effect, and make really difficult its study. We have designed Josephson NanoJunctions in which two S reservoirs are connected through an N layer at a nanoscale, where N is a lightly disordered HTcS, whose Tc has been reduced by ion irradiation. In these SNS junctions, Cooper pairs propagate through the N layer by PE. In this situation with no metallurgical interfaces within the same material, we have shown that a long range PE takes place, which can be quantitatively described by the quasi-classical approach of the diffusive Usadel equations. The Josephson coupling temperature can be computed. The role of the order parameter symmetry will be also discussed.