Topological aspects of dual superconductors

We discuss topological aspects of two-gap superconductors with and without Josephson coupling between gaps. We address nontrivial topological aspects of the dual superconductors and its connections to the Meissner effect and flux quantization. The topological knotted string geometry is also discussed in terms of the Hopf invariant, curvature, and torsion of the strings associated with U(1)×U(1) gauge group.