Stabilizing fractional vortices in multiband superconductors with periodic pinning arrays

Abstract

Multiband superconductors support the excitation of vortices with fractional quantum flux, known as fractional vortices. In the ground state, the fractional vortices in different bands bond together to form a composite vortex with the standard flux quantum $Φ_0$; thus, it is difficult to stabilize the fractional vortices. Here we show that fractional vortex lattices can be stabilized in multiband superconductors with a periodic pinning array at the half matching field of the composite system, when full matching of the fractionalized vortices occurs. In the presence of a high current, the fractional vortices in different bands decouple and move at different velocities. When the current is turned off suddenly, the fractional vortices in different bands may be trapped at different pinning sites. This system also exhibits rich dynamic behavior, and for fractional vortices in two-band superconductors we find a phases where the vortices one band are pinned and the vortices in the other band are moving. These different phases can be observed in transport measurements, and produce a new type of self-induced Shapiro steps that can arise under the application of only a dc drive.