Type-1.5 superconductivity in two-band systems

In the usual Ginzburg-Landau theory the critical value of Ginzburg-Landau parameter inlMMLBox separates regimes of type-I and type-II superconductivity. The latter regime possess thermodynamically stable vortex excitations which interact with each other repulsively and tend to form vortex lattices. It was shown in E. Babaev and J.M. Speight Phys.Rev. B72 (2005) 180502 that this dichotomy in broken in multicomponent Ginzburg-Landau models which possess a distinct phase with vortex excitations which interact attractively at large length scales and repulsively at shorter distances. Here we discuss that similar kind of superconductivity can also arise for entirely different reasons in superconductors where only one band is superconducting if this band interacting via a proximity effect with another band (the report is partially based on [1]).