Local thermodynamic study of correlated insulating ground states and charge excitations in magic-angle twisted bilayer graphene

The flat electronic bands in magic-angle twisted bilayer graphene (MATBG) host a variety of correlated insulating ground states, many of which are predicted to support charged excitations with topologically non-trivial spin and/or valley textures. However, it has remained challenging to experimentally address their ground state order and excitations, both because some of the proposed states do not couple directly to experimental probes, and because they are highly sensitive to spatial inhomogeneities in real samples. In this talk, I will present local electronic compressibility measurement of MATBG using a scanning single-electron transistor. We show thermodynamic evidence for gapped ground states at even integer moiré filling factors at low magnetic fields. Measuring the gap evolution as a function of perpendicular magnetic field sheds light on the nature of the underlying ground state and charge excitations. From the spatial dependence of these states and the chemical potential variation within the flat bands, we infer a link between the stability of the correlated ground states and local twist angle and strain.