Observation of fluxon propagation in asymmetrically based long Josephson junctions

We have investigated the volt-ampere characteristics of long Josephson junctions with various geometries. The VI curve of an asymmetrically biased junction has asymmetric structures with respect to the voltage axis. No such asymmetry was observed in devices with symmetrical bias current distribution. The structures are attributed to the propagation and annihilation of vortices. The junction voltage in the flux flow mode increases linearly with external magnetic field when one increases the field beyond the value necessary to have more than one vortex in the junction. The voltage vs applied magnetic field characteristics, from which the characteristic impedance of the transmission line can be obtained, are in good agreement with theoretical work. A separate linear branch in the VI characteristics was observed in a few devices and is attributed to shorts in parallel with the long junction.