Intervortex quasiparticle tunneling and electronic structure of multi-vortex configurations in type-II superconductors

The electronic spectrum of multi-vortex configurations in type-II superconductors is studied taking account of 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 $\xi$. Analyzing the resulting spectra of vortex clusters bonded by the quasiparticle tunneling we find a transition from a set of degenerate Caroli - de Gennes - Matricon branches to anomalous branches similar to the ones in multi-quanta 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 the bulk systems.