Electric Polarization in a Chern Insulator

We extend the Berry-phase concept of polarization to insulators having a nonzero value of the Chern invariant. The generalization to such Chern insulators requires special care because of the partial occupation of chiral edge states. We show how the integrated bulk current arising from an adiabatic evolution can be related to a difference of bulk polarizations. We also show how the surface charge can be related to the bulk polarization, but only with a knowledge of the wave vector at which the occupancy of the edge state is discontinuous. Furthermore, we present numerical calculations on a model Hamiltonian to provide additional support for our analytic arguments.