Title: "Tuning Electron Correlation in Magic-Angle Twisted Bilayer Graphene Using Coulomb Screening"
Abstract: Since its discovery, the superconducting phase in magic-angle twisted bilayer graphene (tBLG) has attracted immense interests in the science community. However, the origin of this novel phenomenon has remained controversial, largely owing to the lack of available experimental tools to directly probe the underlying mechanism. In this talk, I will discuss recent work studying the superconducting phase in magic-angle tBLG using Coulomb screening. By placing the tBLG in close proximity with a Bernal bilayer graphene, separated by a 3 nm thick barrier, the strength of Coulomb interaction within the twisted bilayer can be directly controlled using charge screening from the Bernal bilayer. Transport measurements show that tuning Coulomb screening has an apparent effect on superconducting phase: as Coulomb interaction is weakened by screening, the stability of superconductivity at the optimal doping is enhanced. The effect of Coulomb screening appears to suggest that electron-phonon coupling is the dominant mechanism for Cooper pair formation, and therefore superconductivity, in magic-angle twisted bilayer graphene.
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