Single fluxon in double-stacked Josephson junctions: Approximate analytic solution

An approximate analytic solution for a single fluxon in double stacked Jose phson junctions (SJJ's) is derived for arbitrary junction parameters and co upling strengths. It is shown that the fluxon in double SJJ's can be charac terized by two components, with different characteristic velocities and pen etration depths. Using the perturbation approach, the second order correcti on is found and the accuracy of the solution is analyzed. Comparison with d irect numerical simulations shows a quantitative agreement between exact an d approximate analytic solutions. It is shown that at high propagation velo cities fluxon may have an unusual shape with inverted magnetic field in the second junction.