Models of strong interaction in flat-band graphene nanoribbons: Magnetic quantum crystals

Graphene-based nanostructures exhibit flat electronic energy bands in their single-particle spectrum. We consider interacting electrons in flat bands of zigzag nanoribbons. We present a protocol for flat-band projection that yields interaction-only tight-binding models. We argue that, at low densities, flat bands can delocalize single-particle basis states to support ferromagnetic quantum crystal ground states.