Intertype superconductivity in ferromagnetic superconductors

In many pnictides the superconductivity coexists with ferromagnetism in an accessible range of temperatures and compositions. Recent experiments revealed that when the temperature of magnetic ordering Tm is below the superconducting transition temperature Tc, highly non-trivial physical phenomena occur. In this work we demonstrate the existence of a temperature window, situated between Tm and Tc, where these intrinsically type-II superconductors are in the intertype regime. We explore analytically and numerically its rich phase diagram characterized by exotic spatial flux configurations-vortex clusters, chains, giant vortices and vortex liquid droplets-which are absent in both type-I and type-II bulk superconductors. We find that the intertype regime is almost independent of microscopic parameters, and can be achieved by simply varying the temperature. This opens the route for experimental studies of the intertype superconductivity scarcely investigated to date. The interplay between ferromagnetism and superconductivity plays an important role in trying to understand the mechanisms of superconductivity in iron-based pnictides. Here, the authors investigate a phenomenon called intertype superconductivity which appears due to a crossover from type II to type I between the superconducting transition temperature and magnetic ordering one.