Fermi Velocity Reduction Of Dirac Fermions Around The Brillouin Zone Center In In2se3-Bilayer Graphene Heterostructures

Emergent phenomena such as unconventional superconductivity, Mott-like insulators, and the peculiar quantum Hall effect in graphene-based heterostructures are proposed to stem from the superlattice-induced renormalization of (moire) Dirac fermions at the graphene Brillouin zone corners. Understanding the corresponding band structure commonly demands photoemission spectroscopy with both sub-meV resolution and large-momentum coverage, beyond the capability of the current state-of-the-art. Here the realization of moire Dirac cones around the Brillouin zone center in monolayer In2Se3/bilayer graphene heterostructure is reported. The renormalization is evidenced by reduced Fermi velocity (approximate to 23%) of the moire Dirac cones and the reshaped Dirac point at the Gamma point where they intersect. While there have been many theoretical predictions and much indirect experimental evidence, the findings here are the first direct observation of Fermi velocity reduction of the moire Dirac cones. These features suggest strong In2Se3/graphene interlayer coupling, which is comparable with that in twisted bilayer graphene. The strategy expands the choice of materials in the heterostructure design and stimulates subsequent broad investigations of emergent physics at the sub-meV energy scale.