# Definition Dirac cones occurs in the band structures of [[graphene|graphene]] and [[topological insulator|topological insulators]] and describe the dispersion relation of massless [[fermion|fermions]]. The cones look like the upper and lower haves of a conical surface and meet at what's called the Dirac point. ![[main-qimg-f4897553481cea6da13dd98a956c7657.png]]