Robust one-dimensional wires in lattice mismatched bilayer graphene

We show that lattice mismatched bilayer graphene can realize robust one-dimensional wires. By considering a single domain wall where the masses of the Dirac electrons change their sign, we establish a general projection principle. This determines how the existence of topological zero-energy domain wall states depends on the direction of the domain wall and locations of the massive Dirac cones inside the bulk Brillouin zone. We generalize this idea for arbitrary patterns of domain walls, showing that the topologically protected states exist only in the presence of an odd number of topological domain walls.