Chiral Anomaly Trapped in Weyl Metals: Nonequilibrium Valley Polarization at Zero Magnetic Field

TL;DR

This paper demonstrates that valley polarization due to the chiral anomaly can occur in Weyl metals without magnetic fields, driven by spatial confinement and disorder, with potential persistence over large scales.

Contribution

It introduces numerical tools to analyze nonequilibrium valley polarization in confined Weyl systems, revealing a finite-size effect called chiral anomaly trapping.

Findings

Valley polarization occurs without external magnetic fields.

Spatial confinement induces chiral bulk states enabling valley polarization.

Long-range disorder suppresses inter-valley scattering, allowing polarization to persist.

Abstract

In Weyl semimetals the application of parallel electric and magnetic fields leads to valley polarization -- an occupation disbalance of valleys of opposite chirality -- a direct consequence of the chiral anomaly. In this work, we present numerical tools to explore such nonequilibrium effects in spatially confined three-dimensional systems with a variable disorder potential, giving exact solutions to leading order in the disorder potential and the applied electric field. Application to a Weyl-metal slab shows that valley polarization also occurs without an external magnetic field as an effect of chiral anomaly "trapping": Spatial confinement produces chiral bulk states, which enable the valley polarization in a similar way as the chiral states induced by a magnetic field. Despite its finite-size origin, the valley polarization can persist up to macroscopic length scales if the disorder potential is sufficiently long ranged, so that direct inter-valley scattering is suppressed and the relaxation then goes via the Fermi-arc surface states.