Mean-field theory for superconductivity in twisted bilayer graphene

Teemu J. Peltonen; Risto Ojajärvi; Tero T. Heikkilä

doi:10.1103/PhysRevB.98.220504

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Mean-field theory for superconductivity in twisted bilayer graphene

Teemu J. Peltonen, Risto Ojajärvi, Tero T. Heikkilä

DOI 10.1103/PhysRevB.98.220504 · Physical Review B

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Abstract

Recent experiments show how a bilayer graphene twisted around a certain magic angle becomes superconducting as it is doped into a region with approximate flat bands. We investigate the mean-field s-wave superconducting state in such a system and show how the state evolves as the twist angle is tuned, and as a function of the doping level. We argue that part of the experimental findings could well be understood to result from an attractive electron-electron interaction mediated by electron-phonon coupling, but the flat-band nature of the excitation spectrum also makes the superconductivity quite unusual. For example, as the flat-band states are highly localized around certain spots in the structure, also the superconducting order parameter becomes strongly inhomogeneous.