One-way edge mode in a magneto-optical honeycomb photonic crystal

We study the edge states in two-dimensional photonic crystals arising from a singular point in k space at which two dispersion surfaces intersect. The zigzag edge states in a honeycomb lattice for TM polarization are analogous to the electronic ones in graphene nanoribbons. Electromagnetic modes at the zigzag edges of such photonic crystals consisting of ferrite rods are allowed to propagate only along one direction. The one-way propagation is insensitive to imperfections on the zigzag edge.