Microscopic model for double-barrier SIS´IS Josephson junctions

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Abstract
As shown elsewhere, double-barrier SIS´IS structures (I is the tunnel barrier, S´ is a thin film with TcS´<TcS) combine advantages of weak links and tunnel junctions, namely they are intrinsically shunted and have therefore non-hysteretic I-V characteristics, while their resistance is controlled by the tunnel barriers rather than by the interlayer material. Such junctions are thus very promising in RSFQ and programmable voltage standard applications. In the present contribution we develop a microscopic model for stationary supercurrent and IcRN product in SIS´IS junctions in the general case of an arbitrary TcS´/TcS ratio and arbitrary barriers. In earlier theoretical papers only a few limited cases were studied. The influence of interlayer thickness, critical temperature TcS´ and barrier asymmetry on IcRN is quantitatively studied within this model. The current-phase relation 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 the theory.