Electrodynamical properties of superconducting contacts

We have studied, experimentally and theoretically, the linear response to a small (d.c. or a.c.) magnetic field in the normal part of a normal-superconducting N/S binary layer. It has been shown that the tunneling characteristic of an N/S sandwich, measured on the N side, is sensitive to the values of the pair potential at points far away from the free surface of the N material. Similar nonlocal effects also appear in the electromagnetic response. The greater the temperature compared to the critical temperature of N, the bigger these effects. Some experimental confirmations of these theoretical predictions have been obtained. The theory also explains: (1) why a Meissner effect has not been observed in Cu for the Pb/Cu systems, down to 1°K; (2) why, on the other hand, the r.f. absorption is much smaller in Cu coated with Pb than in normal Cu.