Theoretical determination of the effect of a screening gate on plasmon-induced superconductivity in twisted bilayer graphene

The microscopic pairing mechanism for superconductivity in magic-angle twisted bilayer graphene remains an open question. Recent experimental studies seem to rule out a purely electronic mechanism due to the insensitivity of the critical superconducting temperature to either a highly doped screening layer or the proximity to a metallic screening gate. In this theoretical work, we explore the role of external screening layers on the superconducting properties of twisted bilayer graphene within a purely electronic mechanism. Consistent with the experimental observations, we find that the critical temperature is unaffected by screening unless the screening layer is closer than 3 nm from the superconductor. Thus, the available transport data are not in contradiction with a plasmon-mediated mechanism. We also investigate other properties of this plasmon-mediated superconductivity, including signatures in the tunneling density of states as probed in spectroscopy experiments.