Dynamic band structure in twisted bilayer graphene near the magic angle*

A twist between the orientations of superposed 2D crystal structures leads to a moiré superstructure which can significantly alter their electronic properties. In the case of superposed graphene layers with small twist angle, the energy band flattens resulting in a slow-down of the charge carriers until, at certain “magic angles”, they come to a complete halt. In this regime, electron-electron interactions become strong leading to the emergence of new correlated phases and topologically protected ballistic channels. Using STM on gated twisted bilayer graphene samples, we study the band structure and the emergence of correlated states as a function of doping and twist-angle near the first magic angle. Far from the magic angle, we observe two van hove singularity (VHS) peaks whose separation allows us to extract the interlayer coupling. Contrary to expectation we find that the interlayer hopping is a function of the twist angle and doping. Upon approaching the magic angle the VHS merge into a single flat band which straddles the charge neutrality point. We observe a dynamic reconstruction of the band structure with gap-like features at certain fillings and a corresponding unique spatial reconstruction of the electronic wave-function.