DC-Driven Fractional Flux Quanta in Two-Band Superconductors

Two-band superconductors host vortices from superfluid condensates of different electron bands. These vortices carry a fractional flux quantum and attract each other, coalescing to form a composite vortex with the whole flux quantum (Formula presented.). However, due to the differences in viscosity and flux of the vortices across different bands, composite vortices may dissociate into fractional components. Here, this study theoretically explores the possibility to control the dissociation of composite vortices into fractional components through dc current and pinning strength variation. To this end, it numerically solves the dynamic equation of motion for a single dc-driven composite vortex in a periodic pinning potential in neglect of the interband Josephson coupling. As the pinning strength increases, this study observes a transition from depinning followed by dissociation in the weak-pinning regime to dissociation from the pinned state in the strong-pinning regime. Within the considered model, under moderately strong pinning, fractional vortices from one condensate may become immobile, while those from the other may even move faster than the original composite vortex just before the dissociation. The revealed pinning- and dc-controlled dissociation of fractional flux quanta appeals for experimental investigation and potential application in fluxonic devices.