Description
Stationary compact fluxon profiles are shown to be exact solutions of the inductively coupled and dc-biased Josephson junction ladder. Such states do not exist in the parallel Josephson junction array which is described by the standard discrete sine-Gordon equation. The term "compact" means that the Josephson phase distribution along the ladder has the structure of the type (…,0,0,0,2\pi,2\pi,2\pi,…) with Josephson phases attaining exactly the 0 or 2\pi values. The phase distribution for the fluxons in the parallel array decays exponentially to 0 and 2\pi.
It is shown that there are compact fluxon and multi- fluxon states which either satisfy the top-bottom antisymmetry or are asymmetric. The anti-symmetric states have zero energy if their topological charge is even and the asymmetric states always have zero energy. Depending on the anisotropy constant the compact fluxons can either coexist with the non-compact states or only compact states are possible. External magnetic field prevents compact state existence.
Compact stationary fluxons in the Josephson junction ladder Andrii O. Prykhodko, Ivan O. Starodub, Yaroslav Zolotaryuk, https://doi.org/10.48550/arXiv.2511.19215
