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 ${\mathit{T}}_{\mathit{c}}$. The length scale for nonlocality is defined by the correlation length for superconducting fluctuations ξ(T) and diverges at ${\mathit{T}}_{\mathit{c}}$. This makes it possible to observe the nonlocal part of the conductance in a multiterminal measurement on a sample of size 2πR∼ξ(T). The local part, originating from the Aslamazov-Larkin correction to the conductivity, exceeds usual meso- scopic interference effects near ${\mathit{T}}_{\mathit{c}}$. 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.