Experimental signatures of the chiral anomaly in Dirac–Weyl semimetals

Abstract

We provide a review of recent experimental results on the chiral anomaly in Dirac/Weyl semimetals. After a brief introduction, we trace the steps leading to the prediction of materials that feature protected 3D bulk Dirac nodes. The chiral anomaly is presented in terms of charge pumping between the chiral Landau levels of Weyl fermions in parallel electric and magnetic fields. The related chiral magnetic effect and chiral zero sound are described. Current jetting effects, which present major complications in experiments on the longitudinal magnetoresistance, are carefully analyzed. We describe a recent test that is capable of distinguishing these semiclassical artifacts from intrinsic quantum effects. Turning to experiments, we review critically the longitudinal magnetoresistance experiments in the Dirac/Weyl semimetals Na3Bi, GdPtBi, ZrTe5 and TaAs. Alternate approaches to the chiral anomaly, including experiments on non-local transport, thermopower, thermal conductivity and optical pump-probe response are reviewed. In the Supplement, we provide a brief discussion of the chiral anomaly in the broader context of high energy physics and relativistic quantum field theory, as well the anomaly's starring role at the nexus of quantum physics and differential geometry.