Many-Body Orbital Paramagnetism in Doped Graphene Sheets

The orbital magnetic susceptibility of a gas of noninteracting massless Dirac fermions is zero when the Fermi energy is away from the Dirac point. Making use of diagrammatic perturbation theory, we calculate exactly the orbital magnetic susceptibility of massless Dirac fermions to first order in the Coulomb interaction demonstrating that it is finite and positive. Doped graphene sheets are thus unique systems in which the orbital magnetic susceptibility is completely controlled by many-body effects.