I've looked through several papers that talk about the anomalous integer quantum Hall effect of graphene (such as http://journals.aps.org/prl/pdf/10.1103/PhysRevLett.95.146801), and they all state that the Hall effect is anomalous for graphene because the n=0 Landau level has half the degeneracy of the n>1 levels, with little to no explanation and without citing any (helpful) sources.

One of the papers (http://journals.aps.org/prb/pdf/10.1103/PhysRevB.75.165411) states that "the Dirac fermions have acquired an effective gap in a form of a “relativistic mass” due to the Coulomb interaction. Such a gap reduces the degeneracy of *only* the zeroth LL." Could someone explain this in more depth, specifically *why* the Coulomb interaction only breaks the degeneracy of the zeroth LL?

This post imported from StackExchange Physics at 2014-05-04 11:25 (UCT), posted by SE-user Izzhov