Generic Chiral Anomaly and Planar Hall Effect in a Non-Weyl System

The condensed-matter version of the chiral anomaly describes how electrons are pumped from a Weyl node with negative chirality to a Weyl node with positive chirality using parallel electric and magnetic fields. Key experimental signatures are a negative longitudinal magnetoresistance (LMR) and the planar Hall effect (PHE), both of which have been experimentally observed. Here, we show that the chiral anomaly explains key features of magnetotransport in the nodal-line semimetal ZrTe$_5$ despite the absence of Weyl points. The anomaly physics applies generically to materials in the quantum limit, when electron transport becomes quasi-one-dimensional, provided that Fermi velocities remain sufficiently large. This explains not only the negative LMR but also the PHE with a gigantic Hall angle and a highly unusual magnetic-field-angle dependence in ZrTe$_5$.