Vortex fractionalization in a Josephson ladder

Abstract

We show numerically that, in a Josephson ladder with periodic boundary conditions and subject to a suitable transverse magnetic field, a vortex excitation can spontaneously breakup into two or more fractional excitations. If the ladder has N plaquettes, and N is divisible by an integer q, then in an applied transverse field of 1/q flux quanta per plaquette the ground state is a regular pattern of one fluxon every q plaquettes. When one additional fluxon is added to the ladder, it breaks up into q fractional fluxons, each carrying 1 / q units of vorticity. The fractional fluxons are basically walls between different domains of the ground state of the underlying 1 / q lattice. The fractional fluxons are all depinned at the same applied current and move as a unit. For certain applied fields and ladder lengths, we show that there are isolated fractional fluxons. It is shown that the fractional fluxons would produce a time-averaged voltage related in a characteristic way to the ac voltage frequency.

Static and dynamic properties of fluxons in a zig-zag Josephson junction

“…Recently, Tornes and Stroud [19] consider fluxon splintering in a one-dimensional periodic array of short Josephson junctions in which junction number n is an nκ-junction. The Josephson supercurrent of a κ junction is proportional to ∝ sin(φ + κ).…”

Unusual Nonlinear Dynamics Observed in NbN Superconducting Microwave Resonators

“…Whereas the nonlinear dynamics of Josephson junctions incorporated in resonant cavities, which was analyzed recently in several theoretical and experimental studies, mainly for the purpose of developing sources of coherent microwave radiation, can be found in Refs. [38,39,40,41,42], and in the cited references therein. Although these works do not analyze the effect of Josephson junctions on the resonance response of the cavity (a single mode is generally assumed), they provide a good understanding of the I-V characteristics of these arrays.…”