"Disordered Dirac Fermions"

I discuss the behavior of three dimensional Dirac fermions with scalar potential disorder. I show that disorder controls the universal behavior at the Dirac point, even though perturbative arguments suggest disorder is an irrelevant perturbation. The effect of disorder is encoded in 'instanton’ contributions that are overlooked by standard disorder averaged calculations. I

discuss the implications for transport in 3D Dirac materials, and some open problems.