Van Hove Singularity and Enhanced Superconductivity in Ca-Intercalated Bilayer Graphene Induced by Confinement Epitaxy.

We demonstrate the impact of high-density calcium introduction into Ca-intercalated bilayer graphene on a SiC substrate, wherein a metallic layer of Ca has been identified at the interface. We have discerned that the additional Ca layer engenders a free-electron-like band, which subsequently hybridizes with a Dirac band, leading to the emergence of a van Hove singularity. Coinciding with this, there is an increase in the critical temperature for superconductivity. These findings allude to the manifestation of Ca-driven confinement epitaxy, augmenting superconductivity through the enhancement of attractive interactions in a pair of electron and hole bands with flat dispersion around the Fermi level.