Direct View of Gate-Tunable Miniband Dispersion in Graphene Superlattices Near the Magic Twist Angle

Z Jiang and D Lee and AJH Jones and Y Park and K Hsieh and P Majchrzak and C Sahoo and TS Nielsen and K Watanabe and T Taniguchi and P Hofmann and JA Miwa and YP Chen and J Jung and S Ulstrup, ACS NANO, 19, 2379-2387 (2025).

DOI: 10.1021/acsnano.4c12905

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

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