Novel Andreev bound states in nanostructured superconductors

We investigate the electronic structure of a superconductor(SC) in proximity of nanoscale ferromagnetic(FM) disc (SC/FM hybrids) and find that the superconductor order parameter has its minimum under the edge of the disc, thus forming a sombrero-like profile. The quasiparticle dispersion for such an order parameter is calculated with quasi-classical Bogoliubov-de Gennes equations. The result shows that the energy versus angular momentum dispersion has a minimum at finite non-zero angular momentum. The low-lying superconducting excitations of this SC/FM nanohbryid are Andreev bound states that possess a large non-zero angular momentum.