Orbital magnetism and transport phenomena in two-dimensional Dirac fermions in a weak magnetic field

We discuss the orbital magnetism and the Hall effect in a weak magnetic field in two-dimensional Dirac fermion systems with an energy gap. This model is related to the graphene sheet, zero-gap organic conductors, and the d-density-wave state of cuprates. We found strong diamagnetism and anomalous Hall conductivity even in gapped systems. We also discuss the relation between results of the weak-magnetic-field formalism and those in a finite magnetic field with Landau quantization.