Abstract

I will talk about our recent experimental observation of very fast dynamically stable 4-pi vortices in arrays of parallel-connected small Josephson junctions [1]. Dynamically stable multiple kinks in discrete sine-Gordon systems were predicted theoretically more than 20 years ago but they have been never seen in experiments until now. By measuring the current-voltage characteristics of specially designed Josephson arrays, we observe propagation of 4-pi-kinks in the form of fast particle-like Josephson vortices. These multiple kinks carry magnetic flux equal to two magnetic flux quanta. At the same value of the bias current, the velocity of 4-pi vortices is about 20% higher than the velocity of ordinary 2-pi vortices. When reducing the bias current, a 4-pi vortex dissociates into a pair of two spatially separated ordinary 2-pi vortices of the same polarity moving at a constant distance from each other. Such metastable bunched states are formed due to interaction between vortices through their oscillatory tails.

[1] J. Pfeiffer, M. Schuster, A. A. Abdumalikov, and A. V. Ustinov,Phys. Rev. Lett. 96, 034103 (2006)