Phase transitions and vortex structures in multicomponent superconductors

Theoretical aspects of multicomponent superconductivity and systems with competing interactions are studied using Monte Carlo techniques. Motivated by recent experimental and theoretical results of complex structure formation of vortices in multicomponent systems, possible vortex structure formations due to vortex interactions that are not purely attractive or repulsive are considered. Vortex structures such as clusters, superclusters, hierarchical structure formation, stripes, gossamer patters, glassy phases, as well as checkerboard lattices and loops are demonstrated to be possible. The order of the superconducting phase transition is considered for multicomponent lattice London superconductors. The phase transition is demonstrated to be either rst-order or continuous depending on the strength of a symmetry-breaking Josephson intercomponent interaction. It is argued that the rst-order phase transition is caused by a vortex phase separation due to a uctuation-induced attractive interaction between vortex lines.