Direct Visualization of Gate-Tunable Flat Bands in Twisted Double Bilayer Graphene

The symmetry-broken correlated states in twisted double bilayer graphene (TDBG) can be tuned via several external knobs, including twist angle, displacement field, and carrier density. However, a direct, momentum-resolved characterization of how these parameters reshape the flat-band structure remains limited. In this Letter, we employ microfocused angle-resolved photoemission spectroscopy to investigate the flat-band dispersion of TDBG at a twist angle of 1.6°, systematically varying the displacement field and carrier density via electrostatic gating. We directly observe multiple flat moiré minibands near charge neutrality, including a flat remote valence band residing below the low-energy flat-band manifold. Furthermore, the dominant Coulomb repulsive energy over the flat-band bandwidth suggests favorable conditions for the emergence of interaction-driven correlated phenomena in TDBG. These findings establish that the formation and evolution of flat bands in TDBG arises from the interplay between the electron filling and the displacement field.