Vortices with fractional flux in two-gap superconductors and in extended Faddeev model

Abstract

We discuss vortices allowed in two-gap superconductors, bilayer systems and in equivalent extended Faddeev model. We show that in these systems there exist vortices which carry an arbitrary fraction of magnetic flux quantum. Besides that we discuss topological defects which do not carry magnetic flux and describe features of ordinary one-magnetic-flux-quantum vortices in the two-gap system. The results should be relevant for the newly discovered two-band superconductor $Mg B_2$.