Chiral orbital current and anomalous magnetic moment in gapped graphene

We present a low-energy effective-mass theory to describe chiral orbital current and anomalous magnetic moment in graphenes with band gap and related materials. We show that a Bloch electron generally contains an anomalous current density due to inter-band matrix elements, which describes a chiral current circulation associated with magnetic moment. In gapped graphenes, the chiral current is opposite between different valleys, and corresponding magnetic moment accounts for valley splitting of Landau levels. In gapped bilayer graphene, in particular, the valley-dependent magnetic moment is responsible for divergence of paramagnetic susceptibility at the band bottom, and full valley polarization is achieved in relatively small magnetic field range. The formulation also applies to the gapped surface states of three-dimensional topological insulator, where the anomalous current is related to the magneto-electric response in spatially-modulated potential.