Minimum critical length for superconductivity in one-dimensional wires

We have experimentally studied the superconducting behavior of one-dimensional aluminum wires of various lengths. Each wire had much wider two-dimensional contact pads on both sides. At a temperature T below ${\mathit{T}}_{\mathit{c}}$, when the wide pads are driven normal by a perpendicular magnetic field, only samples longer than a critical length, ${\mathit{L}}_{\mathit{c}}$≃πξ(T), show evidence for superconductivity. This is a direct confirmation of the prediction by Liniger for a normal-metal–superconductor–normal-metal structure with clean interfaces.