# Magnon quantum anomalies in Weyl ferromagnets

## TL;DR

This paper demonstrates that Weyl ferromagnets can exhibit magnonic quantum anomalies similar to electronic Weyl semimetals, with unique spin and heat current signatures, induced by strain and electromagnetic fields.

## Contribution

It introduces a novel realization of magnon quantum anomalies in Weyl ferromagnets, distinct from Weyl semimetals, through analytical and numerical analysis of Landau quantization and current responses.

## Key findings

- Magnon bands can be Landau-quantized by inhomogeneous electric or pseudo-electric fields.
- Magnons can be pumped by inhomogeneous magnetic or pseudo-magnetic fields.
- Distinct magnon quantum anomalies lead to unique spin and heat currents.

## Abstract

When subjected to parallel electric field $\mathbf E$ and magnetic field $\mathbf B$, Weyl semimetals exhibit the exotic transport property known as the chiral anomaly due to the pumping of electrons between Weyl cones of opposite chiralities. When one or both electromagnetic (EM) fields are replaced by strain-induced chiral pseudo-electromagnetic (pseudo-EM) fields, other types of quantum anomalies occur. In the present paper, we will show that such quantum anomalies can be reproduced in a completely different system -- a Weyl ferromagnet whose magnonic structure remarkably encodes Weyl physics. By analytical and numerical calculations, we will show that the magnon bands can be Landau-quantized by either an inhomogeneous electric field $\mathbf E$ or a chiral pseudo-electric field $\mathbf e$ induced by a torsional strain, and magnons can be pumped along bands by either an inhomogeneous magnetic field $\mathbf B$ or a chiral pseudo-magnetic field $\mathbf b$ due to a dynamic uniaxial strain. We list the magnon quantum anomalies and the associated anomalous spin and heat currents in the Weyl ferromagnet, and show they are distinct from their Weyl semimetal counterparts.