Direct View of Gate-Tunable\nMiniband Dispersion in\nGraphene Superlattices Near the Magic Twist Angle

Superlattices from twisted graphene mono- and bilayer\nsystems give\nrise to on-demand many-body states such as Mott insulators and unconventional\nsuperconductors. These phenomena are ascribed to a combination of\nflat bands and strong Coulomb interactions. However, a comprehensive\nunderstanding is lacking because the low-energy band structure strongly\nchanges when an electric field is applied to vary the electron filling.\nHere, we gain direct access to the filling-dependent low-energy bands\nof twisted bilayer graphene (TBG) and twisted double bilayer graphene\n(TDBG) by applying microfocused angle-resolved photoemission spectroscopy\nto in situ gated devices. Our findings for the two systems are in\nstark contrast: the doping-dependent dispersion for TBG can be described\nin a simple model, combining a filling-dependent rigid band shift\nwith a many-body-related bandwidth change. In TDBG, on the other hand,\nwe find a complex behavior of the low-energy bands, combining nonmonotonous\nbandwidth changes and tunable gap openings, which depend on the gate-induced\ndisplacement field. Our work establishes the extent of electric field\ntunability of the low-energy electronic states in twisted graphene\nsuperlattices and can serve to underpin the theoretical understanding\nof the resulting phenomena.