Observation of the Chiral Anomaly in Dirac and Weyl Semimetals
Abstract: Dirac states protected by symmetry (against gap formation) occur in monolayer graphene and on the surfaces of topological insulators (e.g., Bi2Se3). In both cases, however, the Dirac states are strictly two-dimensional (or 2+1 dimensions in spacetime). In 2012, the semimetals Na3Bi and Cd3As2 were predicted to be Dirac semimetals exhibiting protected 3+1-D Dirac states in the bulk.
Soon after the experimental verification, Weyl states were discovered in the semimetals TaAs and NbAs. A phenomenon long-predicted (1983) to occur in crystals with 3+1-D Dirac states (but not in 2+1-D) is the chiral anomaly. In relativistic field theory, all massless fermions separate into left- and right-handed chiral fermions that don’t mix. However, coupling the fermions to electromagnetic fields (parallel electric and magnetic fields in a crystal) destroys the chiral symmetry, resulting in the appearance of an axial current. This constitutes the chiral anomaly.
I will describe the observation of the chiral anomaly in Na3Bi and the half Heusler metal GdPtBi. In this talk, I will attempt to provide an introductory description of these effects.