Evidence for the chiral anomaly in the Dirac semimetal Na ₃ Bi

TLDR

Dirac semimetals have a graphene‑like electronic structure in three dimensions, and when a magnetic field splits their Dirac cones into left‑ and right‑handed fermions, an electric field parallel to the magnetic field can break chiral symmetry, producing the chiral anomaly. The authors observed the chiral anomaly in Na₃Bi, detecting a large negative magnetoresistance that appears only when the electric and magnetic fields are nearly parallel. Xiong et al.

Abstract

Breaking chiral symmetry in a solid Dirac semimetals have graphene-like electronic structure, albeit in three rather than two dimensions. In a magnetic field, their Dirac cones split into two halves, one supporting left-handed and the other right-handed fermions. If an electric field is applied parallel to the magnetic field, this “chiral” symmetry may break: a phenomenon called the chiral anomaly. Xiong et al. observed this anomaly in the Dirac semimetal Na 3 Bi (see the Perspective by Burkov). Transport measurements lead to the detection of the predicted large negative magnetoresistance, which appeared only when the two fields were nearly parallel to each other. Science , this issue p. 413 , see also p. 378