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

TL;DR

This paper theoretically investigates how external screening layers influence plasmon-mediated superconductivity in twisted bilayer graphene, aligning with experimental data that shows minimal impact on critical temperature.

Contribution

It demonstrates that screening layers only affect superconductivity when very close, supporting the plausibility of a plasmon-mediated pairing mechanism in the material.

Findings

Critical temperature remains unchanged unless screening layer is within 3 nm.

Transport data does not contradict plasmon-mediated superconductivity.

Signatures in tunneling density of states are analyzed.

Abstract

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 nanometers from the superconductor. Thus, the available transport data is 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.