Type-1.5 Superconductor - Type-1.5 Superconductor in Mixtures of Independently Conserved Condensates

Type-1.5 Superconductor in Mixtures of Independently Conserved Condensates

For multicomponent superconductors with so called U(1)xU(1) symmetry the Ginzburg-Landau model is a sum of two single-component Ginzburg-Landau model which are coupled by a vector potential :

where are two superconducting condensates. In case if the condensates are coupled only electromagnetically, i.e. by the model has three length scales: the London penetration length and two coherence lengths . The vortex excitations in that case have cores in both components which are co-centered because of electromagnetic coupling mediated by the field . The necessary but not sufficient condition for occurrence of type-1.5 regime is . Additional condition of thermodynamic stability is satisfied for a range of parameters. These vortices have a nonmonotonic interaction: they attract each other at large distances and repel each other at short distances. It was shown that there is a range of parameters where these vortices are energetically favorable enough to be excitable by an external field, attractive interaction notwithstanding. This results in the formation of a special superconducting phase in low magnetic fields dubbed "Semi-Meissner" state. The vortices, whose density is controlled by applied magnetic flux density, do not form a regular structure. Instead, they should have a tendency to form vortex "droplets" because of the long-range attractive interaction caused by condensate density suppression in the area around the vortex. Such vortex clusters should coexist with the areas of vortex-less two-component Meissner domains. Inside such vortex cluster the component with larger coherence length is suppressed: so that component has appreciable current only at the boundary of the cluster.