Affiliation
Department of Physics, Faculty of Science, National University of Singapore
Title
Theoretical determination of the effect of a screening gate on the superconductivity in twisted bilayer graphene
Abstract
The discovery of superconductivity in magic-angle twisted bilayer graphene (MATBG) has attracted tremendous interest in part due to the similarity of the observed phase diagram with the long-standing problem of high-temperature superconductivity in cuprates. At present, there is no consensus on the microscopic mechanism for superconductivity in a system as simple as two rotated sheets of carbon. Recent experimental studies [Stepanov et al. Nature 583 375 (2020); Saito et al. Nature Physics 926 (2020); Science 371 1261 (2021)] seem to rule out a purely electronic mechanism due to the insensitivity of the critical superconducting temperature with 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. Remarkably, consistent with the experimental observations, we show that the critical temperature is unaffected by screening unless the screening layer is closer than 3 nanometers. We explore other properties of this plasmon-paired superconductor including the non-monotonic dome feature and single-particle density of states.