Dirac cones beyond the honeycomb lattice: A symmetry-based approach

Dirac cones are at the heart of all the quasirelativistic phenomena oberved or predicted to occur in graphene. For a long time, it was believed that their existence is tightly bound to the honeycomb geometry of the graphene lattice. However, recent studies show that Dirac cones can be found in a variety of two-dimensional materials, with square or more complicated lattices. Here, the authors present a complete classification of these different systems, and show how Dirac cones emerge as a consequence of the symmetries of the underlying crystal. These results also provide guidelines to engineer novel materials that go beyond graphene.