Microscopic model for double-barrier SIS'IS Josephson junctions

As shown elsewhere, double-barrier SIS'IS structures (I is the tunnel barri er, S' is a thin film with T-cS' < T-cS) combine advantages of weak links a nd tunnel junctions, namely they are intrinsically shunted and have therefo re non-hysteretic I-V characteristics, while their resistance is controlled by the tunnel barriers rather than by the interlayer material. Such juncti ons are thus very promising in RSFQ and programmable voltage standard appli cations. In the present contribution we develop a microscopic model for sta tionary supercurrent and I-c/R-N product in SIS'IS junctions in the general case of an arbitrary T-cS'/ T-cS ratio and arbitrary barriers. In earlier theoretical papers only a few limited cases were studied. The influence of interlayer thickness, critical temperature T-cS' and barrier asymmetry on I -c/R-N is quantitatively studied within this model. The current-phase relat ion in different parameter ranges and the influence of the electronic mean free path in the S' interlayer is also discussed. It is shown that data for Nb/AlOx/Al/AlOx/Nb junctions from different groups are well described by t he theory.