Аннотация:The interplay between dirty and clean limits in Superconductor-Ferromagnet-Superconductor (SFS) Josephson junctions is a subject of intensive theoretical studies1,2. SIFS junctions, containing an additional insulator (I) barrier are interesting as potential logic elements in superconducting circuits, since their critical current Ic can be tuned over a wide range, still keeping a high IcRN product, where RN is the normal resistance of the junction. They are also a convenient model system for a comparative study of the 0-π transitions for arbitrary relations between characteristic lengths of the F-layer: the layer thickness d, the mean free path l, the magnetic length ξH=vF/2H, and the nonmagnetic coherence length ξ0=vF/2πT, where vF is the Fermi velocity, H is the exchange magnetic energy, and T is the temperature. The spatial variations of the order parameter are described by the complex coherent length in the ferromagnet ξF-1= ξ1-1+ iξ2-1. It is well known, that in the dirty limit (l<<ξ1,2) described by the Usadel equations both ξ12=ξ22= vFl/3H .
In this work the spatial distribution of the anomalous Green’s functions and the Josephson current in the SIFS junction are calculated. The linearized Eilenberger equations are solved together with the Zaitsev boundary conditions. This allows comparing the dirty and the clean limits, investigating a moderate disorder, and establishing the applicability limits of the Usadel equations for such structures. We demonstrate that for an arbitrary relation between l, ξH, and d the spatial distribution of the anomalous Green’s function can be approximated by a single exponent with reasonable accuracy, and we find its effective decay length and oscillation period for several values of ξH, l and d. The role of different types of the FS interface is analyzed. The applicability range of the Usadel equation is established.
The results of calculations have been applied to the interpretation of experimental data3 obtained on Nb-Al2O3-Cu-Ni-Nb Josephson junctions containing a Ni layer with moderate scattering.
