Spectroscopic Evidence for Electron Correlations in Epitaxial Bilayer Graphene with Interface-Reconstructed Superlattice Potentials

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 6 \times 6 interface reconstruction phase, the spectral-weight transfer occurs between the two broad peaks flanking the charge-neutral point. Such a 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 6 \times 6 reconstruction as in magic-angle BLG by the moiré potentials. Quantitative analysis suggests that the intrinsic interface reconstruction shows a high carrier tunability of \sim 1/2 filling range, equivalent to the back gating by a voltage of \sim 70 V in a typical gated BLG/SiO_2/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.