Nonlinear electrical transport unveils Fermi surface malleability in a moir\'e heterostructure

TL;DR

This study uses nonlinear electrical transport measurements to reveal how the Fermi surface in twisted bilayer graphene changes with electron density, providing new insights into its band topology and correlated states.

Contribution

It introduces nonlinear transport as a novel method to probe Fermi surface topology and band structure in moiré heterostructures at zero magnetic field.

Findings

Nonlinear responses map Fermi surface reconstructions.

Berry curvature dipole influences nonlinear signals.

Nonlinear transport complements linear Hall measurements.

Abstract

Van Hove singularities enhance many-body interactions and induce collective states of matter ranging from superconductivity to magnetism. In magic-angle twisted bilayer graphene, van Hove singularities appear at low energies and are malleable with density, leading to a sequence of Lifshitz transitions and resets observable in Hall measurements. However, without a magnetic field, linear transport measurements have limited sensitivity to the band's topology. Here, we utilize nonlinear longitudinal and transverse transport measurements to probe these unique features in twisted bilayer graphene at zero magnetic field. We demonstrate that the nonlinear responses, induced by the Berry curvature dipole and extrinsic scattering processes, intricately map the Fermi surface reconstructions at various fillings. Importantly, our experiments highlight the intrinsic connection of these features with the moir\'e bands. Beyond corroborating the insights from linear Hall measurements, our findings establish nonlinear transport as a pivotal tool for probing band topology and correlated phenomena.