Double stacked superconducting junctions for investigating the proximity effect in Nb/Al bilayers

Experimental investigations on the proximity effect in Nb/Al bilayers by using Nb/AlOy/Nb/Al/AlxOy/Nb structures with different Al thickness are reported. Three-terminal stacked devices were fabricated by using a new process based on a whole-wafer deposition of the multilayer without any vacuum breaking in order to ensure a high control of the interfaces. The quasiparticle density of states at both sides of the bilayer and the effective interface coupling parameters were obtained by a deconvolution of the I-V data. They were compared with numerical calculations based on the microscopic model proposed by Golubov et al. [Phys. Rev. B 51 (1995) 1073] for the proximity effect in spatially inhomogeneous bilayers. The investigation has been also performed in the presence of steady-state injection at different quasiparticle energies