Axial anomaly generation by domain wall motion in Weyl semimetals

TL;DR

This paper explores how domain wall motion in magnetic Weyl semimetals induces axial electromagnetic fields that activate the axial anomaly, leading to observable electromagnetic radiation as a direct signature.

Contribution

It introduces a novel mechanism linking domain wall dynamics to axial anomaly activation and proposes an experimental signature through electromagnetic radiation.

Findings

Axial electric and magnetic fields localized at domain walls.

Activation of the axial anomaly via domain wall motion.

Electromagnetic radiation as a signature of the axial anomaly.

Abstract

A space-time dependent node separation in Weyl semimetals acts as an axial vector field. Coupled with domain wall motion in magnetic Weyl semimetals, this induces axial electric and magnetic fields localized at the domain wall. We show how these fields can activate the axial (chiral) anomaly and provide a direct experimental signature of it. Specifically, a domain wall provides a spatially dependent Weyl node separation and an axial magnetic field $\textbf{B}_5$, and domain wall movement, driven by an external magnetic field, gives the Weyl node separation a time dependence, inducing an axial electric field $\textbf{E}_5$. At magnetic fields beyond the Walker breakdown, $\textbf{E}_5\cdot\textbf{B}_5$ becomes nonzero and activates the axial anomaly that induces a finite axial charge density -- imbalance in the number of left- and right-handed fermions -- moving with the domain wall. This axial density, in turn, produces, via the chiral magnetic effect, an oscillating current flowing along the domain wall plane, resulting in a characteristic radiation of electromagnetic waves emanating from the domain wall. A detection of this radiation would constitute a direct measurement of the axial anomaly induced by axial electromagnetic fields.