NONLOCAL EFFECTS IN MESOSCOPIC SUPERCONDUCTING AL STRUCTURES

We have measured the magnetoresistance R(B) and the magnetic phase bou ndaries T-c(B) of a mesoscopic superconducting Al loop and of the lead s connected to the loop. Pronounced oscillations with flux period h/2e of R(B) and T-c(B) are observed for the loop as well as for the leads . At low magnetic fields the oscillation amplitude Delta T-c(B) of the loop is suppressed when compared to the usual Little-Parks oscillatio ns in Al microcylinders. With increasing magnetic field, Delta T-c(B) for the loop rises to the theoretically expected value, while the nonl ocal oscillations in the leads are dying out. The results can be under stood in terms of a proximity effect coupling between the leads and th e loop, which is weakened when the temperature dependent coherence len gth decreases.