  Superlattices from twisted graphene mono- and bi-layer systems give rise to
on-demand quantum many-body states such as Mott insulators, unconventional
superconductors and the fractional quantum Hall effect. These phenomena are
observed in transport experiments when changing the filling of the low-energy
electronic bands. Their origin is broadly ascribed to a combination of flat
bands and strong Coulomb interactions, yet a comprehensive understanding is
lacking. This is primarily because the relevant low-energy band structure is
believed to strongly change in a non-trivial way as the electron filling is
varied. 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 micro-focused 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 behaviour of
the low-energy bands, combining non-monotonous bandwidth changes and tuneable
gap openings. 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.
