Berry Curvature Dipole in Strained Graphene: A Fermi Surface Warping Effect

It has been recently established that optoelectronic and nonlinear transport experiments can give direct access to the dipole moment of the Berry curvature in nonmagnetic and noncentrosymmetric materials. Thus far, nonvanishing Berry curvature dipoles have been shown to exist in materials with substantial spin-orbit coupling where low-energy Dirac quasiparticles form tilted cones. Here, we prove that this topological effect does emerge in two-dimensional Dirac materials even in the complete absence of spin-orbit coupling. In these systems, it is the warping of the Fermi surface that triggers sizable Berry dipoles. We show indeed that uniaxially strained monolayer and bilayer graphene, with substrate-induced and gate-induced band gaps, respectively, are characterized by Berry curvature dipoles comparable in strength to those observed in monolayer and bilayer transition metal dichalcogenides