Giant vortices, rings of vortices, and reentrant behavior in type-1.5 superconductors

We predict that in a bulk type-1.5 superconductor, the competing magnetic responses of the two components of the order parameter can result in group-stabilized giant vortices and individual rings of vortices in the absence of any extrinsic pinning or confinement mechanism. We also determine within the Ginzburg-Landau theory a condition for the robustness of type 1.5 in the vicinity of the critical temperature, and we find a rich phase diagram with successions of behaviors such as type 1 -> type 1.5 -> type 2 -> type 1.5 when temperature decreases.