Intervortex quasiparticle tunneling and the electronic structure of multivortex configurations in type-II superconductors

The electronic spectrum of multivortex configurations in type-II superconductors is studied taking into account the effect of quasiparticle tunneling between the vortex cores. The tunneling is responsible for the formation of strongly coupled quasiparticle states for intervortex distances a < a(c) where the critical distance a(c) is of the order of several coherence lengths xi. When analyzing the resulting spectra of vortex clusters bonded by quasiparticle tunneling, we find a transition from a set of degenerate Caroli-de Gennes-Matricon branches to anomalous branches similar to the ones in multiquantum giant vortices. This spectrum transformation results in the oscillatory behavior of the density of states at the Fermi level as a function of a and could be observed in mesoscopic superconductors and disordered flux line arrays in bulk systems.