Dirac Semimetal in Three Dimensions

We show that the pseudorelativistic physics of graphene near the Fermi level can be extended to three dimensional (3D) materials. Unlike in phase transitions from inversion symmetric topological to normal insulators, we show that particular space groups also allow 3D Dirac points as symmetry protected degeneracies. We provide criteria necessary to identify these groups and, as an example, present ab initio calculations of β-cristobalite BiO2 which exhibits three Dirac points at the Fermi level. We find that β-cristobalite BiO2 is metastable, so it can be physically realized as a 3D analog to graphene.