Nonlinear electrical transport unveils Fermi surface malleability in a moiré heterostructure

Graphene moiré superlattices host van Hove singularities appear at low energies, which are malleable with progressive band filling, leading to a sequence of Lifshitz transitions and resets observable in Hall measurements. However, at zero magnetic fields, transport measurements in the linear response regime have limited sensitivity to the band's topology. Here, we probe these unique features in twisted bilayer graphene at zero magnetic field using second-order transport measurements. We demonstrate that the nonlinear responses, induced by the Berry curvature dipole and extrinsic scattering processes, intricately map the Fermi surface reconstructions at various partial fillings of the band. Importantly, our study confirms that the applied magnetic field does not induce or stabilize the probed transitions, highlighting these features as intrinsic to the moiré bands. Additionally, we show the tunability of the Berry curvature dipole and extrinsic scattering process with an out-of-plane electric field near the conduction band edge. Beyond corroborating the insights from linear Hall measurements, our findings establish nonlinear transport as a pivotal tool for probing band topology and correlated phenomena.