DC-driven separation of fractional flux quanta in two-band superconductors

Abstract

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 $\phi_0$. However, due to the differences in viscosity and flux of the vortices across different bands, composite vortices may dissociate into fractional components. Here, we theoretically explore an approach to control the dissociation of composite vortices into fractional components and their separation into stationary and fast-moving ones through dc current and pinning strength variation. To this end, we numerically solve the dynamic equation of motion for a single dc-driven composite vortex in a periodic pinning potential. As the pinning strength increases, we observe a transition from depinning followed by dissociation in the weak-pinning regime to dissociation from the pinned state in the strong-pinning regime. 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 predicted pinning- and dc-controlled separation of fractional flux quanta appeals for experimental investigation and potential application in fluxonic devices.