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.

中文翻译：

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外尔金属中的手性异常：零磁场下的非平衡谷极化

在外尔半金属中，平行电场和磁场的应用导致谷极化——相反手性谷的占据不平衡——手性异常的直接后果。在这项工作中，我们提出了数值工具来探索具有可变无序电位的空间受限的三维系统中的这种非平衡效应，给出无序电位和外加电场的领先顺序的精确解。外尔金属板的应用表明，在没有外部磁场的情况下，由于手性异常“俘获”的影响，谷极化也会发生：空间限制产生手性体态，这使得谷极化以类似于由一个磁场。尽管它的起源是有限的，