Local spectroscopic study of moiré band flattening and correlated gaps in magic-angle twisted bilayer graphene*

Magic angle (~1.1°) twisted bilayer graphene (TBG) shows a wide range of correlated electronic states that originate from the flat moiré bands. Scanning tunneling spectroscopy experiments on TBG near the magic angle observed, a large separation between van Hove singularities and finite Dirac velocities signaling relatively large bandwidth that is not compatible with the continuum model expectations. While these previous measurements highlight the presence of electronic interactions, their impact on the band structure is still unclear. Here, we report scanning tunneling spectroscopy measurements of TBG across the area where the twist angle slowly changes from non-magic to magic-angle value. By systematically following the evolution of the moiré electronic bands, we study doping dependent band deformations. Surprisingly, we discover interaction-driven band flattening that can be also related to gap opening near half-filling. Our results provide crucial insights into the robustness of half-filling correlated phases.