Excitations from Filled Landau Levels in Graphene

We consider particle-hole excitations of graphene over an integer quantum hall state. We first analyze the two-body problemof a single Dirac electron and hole in a magnetic field interactingvia Coulomb forces. We then turn to the many-body problem, where particle-hole symmetry and the existence of two valleys lead to a number of effects peculiar to graphene. The appearance of different branches in the exciton spectrum is sensitive to the filling factor. The coupling together of a large number of low-lying excitations leads to strong many- body corrections, which could be observed in inelastic light scattering or optical absorption.