Resonating-valence-bond superconductor from small Fermi surface in twisted bilayer graphene
This work proposes that superconductivity in twisted bilayer graphene arises from an unconventional normal state called the second Fermi liquid (sFL), which has small hole pockets. Superconductivity emerges near the transition from this sFL to a conventional Fermi liquid, driven by pre-existing pairing of local moments mediated by optical phonons. The theory explains the pseudogap and two-gap structure in superconductors.