In-gap corner states in core-shell polygonal quantum rings
  We study Coulomb interacting electrons confined in polygonal quantum rings. We focus on the interplay of localization at the polygon corners and Coulomb repulsion. Remarkably, the Coulomb repulsion allows the formation of in-gap states, i.e. corner-localized states of electron pairs or clusters shifted to energies that were forbidden for uncoupled electrons, but below the energies of side-localized states. We also specify conditions allowing optical excitation of those states. 
Anna Sitek, Mugurel Tolea, Marian Nita, Lloren\c{c} Serra, Vidar   Gudmundsson, Andrei Manolescu
cond-mat.mes-hall