Chiral anomaly factory: Creating Weyl fermions with a magnetic field

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 Td, D4h, and D6h point groups. For the Td point group, we find thatWeyl nodes persist for all directions of the magnetic field. Further, we compute the anomalous magnetoresistance of field-createdWeyl fermions in the semiclassical regime. We find that the magnetoresistance can scale nonquadratically with magnetic field, in contrast to materials with intrinsicWeyl nodes. Our results are relevant to future experiments in the semiclassical regime.