Modelling the energy gap in transition metal/aluminium bilayers

We present an application of the generalised proximity effect theory. The t heory has been used to determine the energy gap (Delta (g)) in proximised t ransition metal/aluminium bilayer structures such as Nb/Al, Ta/Al, V/Al and Mo/Al. These bilayers have different film thicknesses ranging from 5 to 26 0 nm. For the cases of Nb/Al, Ta/Al and V/Al bilayers, the interface parame ters gamma and gamma (BN) (here we define gamma as the ratio of the product s of normal state resistivity and coherence length in each film of the bila yer while YEN is the ratio of the boundary resistance between films 1 and 2 to the product of the resistivity and coherence length in the second fr, w hich were used as input parameters to the model, were inferred experimental ly from an existing bilayer of each kind and then suitably modified for dif ferent film thicknesses. This experimental assessment is therefore based on a comparison of measurements of the critical temperature and the energy ga p at 300 mK with the predictions from the model for various values of gamma , gamma (BN) The energy gap of the bilayer was experimentally determined by using symmetrical superconducting tunnel junctions (STJs) of the form S-Al -AlOx-Al-S, where each electrode corresponds to a proximised bilayer. Howev er for the case of Mo/Al bilayers the interface parameters were determined theoretically since currently no STJ data for this configuration are availa ble. The results for the Nb/Al, Ta/Al and V/Al bilayers have also then been compared to experimentally determined energy gaps found for a series of ST Js with different film thicknesses. The correspondence between experiment a nd theory is very good. (C) 2001 Elsevier Science B.V. All rights reserved.