Tunable large Berry dipole in strained twisted bilayer graphene

Twisted bilayer graphene is highly sensitive to external perturbations. Strains, and the presence of the substrate, break the symmetries of the central bands. The resulting changes in the Berry curvature lead to valley currents and to a nonlinear Hall effect. We show that these effects, described by a Berry dipole, can be very significant, such that the nonlinear effects surpass the linear response for moderate applied fields, ∼0.1mV/μm. The dependence of these effects on applied strain, coupling to the substrate, density of carriers, and temperature, makes them highly tunable.