NONLOCAL RESISTANCE OSCILLATIONS NEAR THE SUPERCONDUCTING TRANSITION

It is shown that the current response to an electric field is strongly nonlocal slightly above the superconducting transition temperature T(c). The length scale for nonlocality is defined by the correlation length for superconducting fluctuations xi(T) and diverges at T(c). This makes it possible to observe the nonlocal part of the conductance in a multiterminal measurement on a sample of size 2piR is-similar-to xi(T). The local part, originating from the Aslamazov-Larkin correction to the conductivity, exceeds usual mesoscopic interference effects near T(c). We use a simple approach (the time-dependent Ginzburg-Landau equation) to calculate the nonlocal resistances for a ring geometry. We predict that the ratio of voltages measured by two different sets of probes attached to the same ring should oscillate as a function of the flux with a period equal to the "superconducting" flux quantum. This is strikingly different from the known Aharonov-Bohm effect for rings made of a "dirty" normal metal, where such a ratio should be flux independent.