PROXIMITY EFFECT IN SUPERCONDUCTING TUNNEL-JUNCTIONS WITH BILAYER ELECTRODES

A wide variety of theories exists for modelling the proximity effect i n superconductor/normal metal bilayers. However, their predictions of the resultant energy gap, its temperature dependence and the tunneling density of states are generally only qualitatively correct. In order to test these theories we have fabricated tunnel junctions with bilaye r electrodes from a variety of different materials and have found that the relatively simple McMillan model agrees quantitatively in most ca ses. In addition, we have shown theoretically that the major undetermi ned parameter of this model, the transmission factor sigma, may be det ermined exactly from fundamental quantities.