Dynamics of Semifluxons in Nb Long Josephson 0-π Junctions

We propose, implement, and test experimentally long Josephson 0-π junctions fabricated using conventional Nb-AlO_x-Nb technology. We show that by using a pair of current injectors one can create an arbitrary discontinuity of the Josephson phase and, in particular, a π discontinuity, just as in d-wave/s-wave or in d-wave/d-wave junctions, and study fractional Josephson vortices which spontaneously appear. Moreover, using such junctions, we can investigate the dynamics of the fractional vortices—a domain which is not yet available for natural 0-π junctions due to their inherently high damping. We observe half-integer zero-field steps which appear on the current-voltage characteristics due to the hopping of semifluxons.