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 C${}_{60}$ in which a violation of Hund's first rule plays a central role.

8 pages, 3 figures