Strong coupling effects in (Nb−Al−AlOx)2-Nb stacked Josephson junctions

Abstract

Stacked (Nb−Al−AlOx)2-Nb long Josephson junctions with very thin intermediate Nb-Al superconducting layer are investigated experimentally and theoretically. Stable coherent in-phase zero-field steps (ZFS's) are observed; both the critical current and the maximum ZFS current dependence on magnetic field are measured to prove the in-phase nature of this mode. The dependences are in good agreement with the inductive coupling model. The Swihart velocities for in-phase (c+) and antiphase (c−) modes are measured for different lengths of the stacks. In order to make a proper interpretation of the experimental results, an extension of the existing model is developed, taking into account the fact that the middle electrode consists of two different superconductors (Nb and proximized Al). A comparison of a new model with the conventional model and experimental data is made. The extended model gives the c+/c− ratio as 30% different from what the conventional model predicts. For thin Nb and Al layers the correction factor depends only on the ratio of the magnetic field penetration depths in Nb and proximized Al.

Source-reported materials — not catalogue approval

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