SOLITON BUNCHING IN ANNULAR JOSEPHSON-JUNCTIONS

By studying soliton (fluxon) motion in long annular Josephson junction s it is possible to avoid the influence of the boundaries and soliton- soliton collisions present in linear junctions. A new experimental des ign consisting of a niobium coil placed on top of an annular junction has been used to insert individual fluxons or antifluxons into the jun ction in a controllable way. The dynamical behavior of different numbe rs of trapped fluxons was investigated. In addition, we were able to c hange the junction parameters by changing temperature. In some of the zero-field steps, the experiments reveal a small jump to higher values of the voltage at the top of the steps, This phenomenon can be caused by a crossover from a nonbunched state to a bunched state of the flux on motion. By performing direct numerical simulations using the pertur bed sine-Gordon equation with parameter values determined from the exp eriments we have been able to confirm the above explanation. (C) 1996 American Institute of Physics.