  Superlattice potentials are theoretically predicted to modify the
single-particle electronic structures. The resulting
Coulomb-interaction-dominated low-energy physics would generate highly novel
many-body phenomena. Here, by in situ tunneling spectroscopy, we show the
signatures of superstructure-modulated correlated electron states in epitaxial
bilayer graphene (BLG) on 6H-SiC(0001). As the carrier density is locally
quasi-'tuned' by the superlattice potentials of a 6x6 interface reconstruction
phase, the spectral-weight transfer occurs between the two broad peaks flanking
the charge-neutral point. Such detected non-rigid band shift beyond the
single-particle band description implies the existence of correlation effects,
probably attributed to the modified interlayer coupling in epitaxial BLG by the
6x6 reconstruction as in magic-angle BLG by the Moire potentials. Quantitative
analysis suggests the intrinsic interface reconstruction shows a high carrier
tunability of around 1/2 filling range, equivalent to the back gating by a
voltage of around 70 V in a typical gated BLG/SiO2/Si device. The finding in
interface-modulated epitaxial BLG with reconstruction phase extends the BLG
platform with electron correlations beyond the magic-angle situation, and may
stimulate further investigations on correlated states in graphene systems and
other van der Waals materials.
