Nonlocal conductance of small superconducting loops in the paraconductive regime

Abstract

Both quasiparticles and superconducting fluctuations contribute to the conductance of superconductors in the paraconductive regime slightly above the transition temperature. The fluctuation contribution consists of the Maki-Thompson correction, which results from the scattering of electrons by a superconducting fluctuation, and the Aslamazov-Larkin contribution which describes the conductivity of a fluctuating electron pair. The latter is nonlocal over a length scale set by the fluctuation correlation length, ξ( T). The observation of this nonlocality involves a multi-terminal measurement of voltages in the paraconductive regime of a square superconducting loop of characteristic size, L ∼ ξ( T). The ratio of the voltages measured by two different sets of probes attached to the loop at different positions is found to oscillate as a function of the flux threading the loop. This effect is distinct from phenomena associated with the coherent transport of electrons in mesoscopic structures of a size smaller than the dephasing length, L φ.