Phases of a phenomenological model of twisted bilayer graphene

Understand

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.