Fluxon dynamics in discrete Josephson transmission lines with stacked junctions

Parallel one-dimensional arrays composed of double-layer stacked small Josephson tunnel junctions were experimentally and numerically investigated. In addition to various features already known for classic single-layer arrays, a new resonant state which corresponds to the locking of the fluxon oscillations to a frequency of small-amplitude oscillations of the superconducting phase in middle islands of small stacks was discovered. Numerical simulations of a simplified circuit were in agreement with experiments and confirmed the proposed qualitative mechanism. There was no proof for the so-called multiple-fluxon propagation in double-junction arrays.