"Phases of a phenomenological model of twisted bilayer graphene"

Abstract:

We propose a lattice-scale two-band generalized Hubbard model as a caricature of the electronic structure of twisted bilayer graphene. Various possible broken-symmetry phases can arise, including a nematic phase (which is a form of orbital ferromagnet) and an orbital-triplet spin-singlet superconducting phase. Concerning the mechanism of superconductivity, we propose an analogy with superconductivity in alkali-doped C₆₀ in which a violation of Hund’s first rule plays a central role.