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.
Highlights
The smallest number of Weyl fermions realizable as quasiparticles in a crystal is two [1,2]—one left handed and one right handed
Reactive components dominate the electromagnetic fields in the near field, and by describing the electromagnetic fields in this limit as an expansion in r/c, we find that the only radiative contribution up to second order in r/c originates from the anomaly current
We have shown how field-driven motion of a domain wall in a magnetic Weyl semimetal leads to the activation of the axial anomaly
Summary
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. At magnetic fields beyond the Walker breakdown, E5 · B5 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
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