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

Motivated by recent experiments in twisted bilayer graphene with an additional screening layer [Stepanov et al. Nature 583 375 (2020); Saito et al. Nature Physics 926 (2020); Science 371 1261 (2021)], we study theoretically the effect of a screening layer on the superconducting transition temperature. It is widely believed that a plasmonic origin, but not a phononic origin of superconductivity will be strongly suppressed by a screening gate. We find that the situation is more complicated: For a plasmonic pairing mechanism [1], we find a metallic screening gate has only a weak effect on superconducting transition for distances larger than 10 nm. At short screening distances, we find that the transition temperature has a non-monotonic dependence on the screening layer carrier density which provides a clear experimental signature to test for a plasmonic origin of the observed superconductivity.

[1] G. Sharma, M. Trushin, O. P. Sushkov, G. Vignale, and S. Adam, Phys. Rev. Research 2, 022040(R) (2020)