Theory of Correlated Insulators and Superconductivity in Twisted Bilayer Graphene

Gal Shavit; Erez Berg; Ady Stern; Yuval Oreg

doi:10.1103/PhysRevLett.127.247703

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Theory of Correlated Insulators and Superconductivity in Twisted Bilayer Graphene

Gal Shavit, Erez Berg, Ady Stern, Yuval Oreg

DOI 10.1103/PhysRevLett.127.247703 · Physical Review Letters

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Abstract

We introduce and analyze a model that sheds light on the interplay between correlated insulating states, superconductivity, and flavor-symmetry breaking in magic angle twisted bilayer graphene. Using a variational mean-field theory, we determine the normal-state phase diagram of our model as a function of the band filling. The model features robust insulators at even integer fillings, occasional weaker insulators at odd integer fillings, and a pattern of flavor-symmetry breaking at noninteger fillings. Adding a phonon-mediated intervalley retarded attractive interaction, we obtain strong-coupling superconducting domes, whose structure is in qualitative agreement with experiments. Our model elucidates how the intricate form of the interactions and the particle-hole asymmetry of the electronic structure determine the phase diagram. It also explains how subtle differences between devices may lead to the different behaviors observed experimentally. A similar model can be applied with minor modifications to other moiré systems, such as twisted trilayer graphene.