Homogenization of the nonlinear graphene currents on hexagonal boron nitride with moiré Berry dipoles

Nonlinear Hall-like currents can be generated by a time-periodic alternating bias on two-dimensional (2D) materials lacking inversion symmetry. Theoretically, the nonlinear response is constrained to a direction normal to the bias field, while experiments in moiré systems have shown a current parallel to the bias as well. To demonstrate that the moiré between graphene and its supporting substrate contributes to this homogeneity of nonlinear currents, a local Berry dipole D over the moiré unit cell is obtained. By calculating ab initio changes in the local potential ∆V(r) around graphene due to a homobilayer of hexagonal boron nitride (hBN), corrections to on-site energies and hopping matrix elements are obtained, which renormalize graphene’s tight-binding electronic dispersion of π−electrons and give rise to a nonzero D, which is seen to change orientation throughout the moiré. In particular, D is shown to wind around high symmetry points in the moiré unit cell. In a semiclassical transport picture, this could lead to nonlinear currents both normal and parallel to the bias field.

Refs.

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