Absence of enhanced superconductivity in double-barrier superconducting tunnel junctions: Measurements of lateral electric transport in the middle normal-metal layer

The lateral conductivity of the middle Al layer of a Nb/Al/AlOx/Al/AlOx/Al/Nb (SINIS) multiterminal device is studied as a function of the current injected perpendicular to the layers in a regime where a gap-difference-like feature is observed in the current-voltage characteristic. The response of the Al layer does not confirm an earlier reported observation of superconductivity in the Al far above its transition temperature [Blamire , Phys. Rev. Lett. 66, 220 (1991)].