Nonlocal effects in mesoscopic superconducting aluminum structures

We have measured the magnetoresistance and the magnetic phase boundary $T_c\mathrm{}\left(B\right)\mathrm{}$ of mesoscopic superconducting Al structures containing a loop. The structures were designed to study the nonlocal character of the superconducting condensate confined by the loop and the electrical leads connected to it. Voltage probes have been attached at several positions to monitor the superconducting transition of both the loop and the segments of the leads. Strong-coupling effects have been found to exist between the loop and the leads. At low magnetic fields, $T_c\mathrm{}\left(B\right)\mathrm{}$ of the lead segments reveals a pronounced oscillatory component, while the oscillation amplitude of $T_c\mathrm{}\left(B\right)\mathrm{}$ of the loop is significantly reduced when compared to the usual Little-Parks effect. The coupling strength is controlled by the temperature-dependent superconducting coherence length.