The chiral anomaly factory: Creating Weyl fermions with a magnetic field

TL;DR

This paper analyzes how magnetic fields create Weyl fermions in certain symmetric materials, classifies their properties, and predicts unique magnetoresistance behaviors, aiding future experimental research.

Contribution

It provides a comprehensive symmetry-based classification of Weyl points created by magnetic fields in specific crystal groups and predicts their magnetoresistance scaling.

Findings

Weyl nodes persist for all magnetic field directions in T_d symmetry.

Magnetoresistance can scale non-quadratically with magnetic field.

Results are relevant for future semi-classical regime experiments.

Abstract

Weyl fermions can be created in materials with both time reversal and inversion symmetry by applying a magnetic field, as evidenced by recent measurements of anomalous negative magnetoresistance. Here, we do a thorough analysis of the Weyl points in these materials: by enforcing crystal symmetries, we classify the location and monopole charges of Weyl points created by fields aligned with high-symmetry axes. The analysis applies generally to materials with band inversion in the $T_d$, $D_{4h}$ and $D_{6h}$ point groups. For the $T_d$ point group, we find that Weyl nodes persist for all directions of the magnetic field. Further, we compute the anomalous magnetoresistance of field-created Weyl fermions in the semiclassical regime. We find that the magnetoresistance can scale non-quadratically with magnetic field, in contrast to materials with intrinsic Weyl nodes. Our results are relevant to future experiments in the semi-classical regime.