Atomic collapse and quasi-Rydberg states in graphene.

Charge impurities in graphene can host an infinite family of Rydberg-like resonance states of massless Dirac particles. These states, appearing for supercritical charge, are described by Bohr-Sommerfeld quantization of collapsing classical trajectories that descend on point charge, in analogy to the hydrogenic Rydberg states relation with planetary orbits. Strong tunnel coupling of these states to the Dirac continuum leads to resonance features in scattering on the impurities that manifest themselves in transport properties and in the local density of states.