Probing the chiral anomaly with nonlocal transport in three dimensional topological semimetals

TL;DR

This paper proposes a nonlocal transport method to detect the chiral anomaly in Weyl and Dirac semimetals, demonstrating how magnetic fields induce measurable valley imbalances that reveal topological properties.

Contribution

It introduces a novel nonlocal transport experiment to measure the chiral anomaly and extends the concept to Dirac semimetals with potential valleytronic applications.

Findings

Nonlocal voltage signals depend on the alignment of magnetic field and current.

The effect is suppressed when magnetic field and current are orthogonal.

Valley currents can be manipulated using electric and magnetic fields.

Abstract

Weyl semimetals are three-dimensional crystalline systems where pairs of bands touch at points in momentum space, termed Weyl nodes, that are characterized by a definite topological charge: the chirality. Consequently, they exhibit the Adler-Bell-Jackiw anomaly, which in this condensed matter realization implies that application of parallel electric ($\mathbf{E}$) and magnetic ($\mathbf{B}$) fields pumps electrons between nodes of opposite chirality at a rate proportional to $\mathbf{E}\cdot\mathbf{B}$. We argue that this pumping is measurable via nonlocal transport experiments, in the limit of weak internode scattering. Specifically, we show that as a consequence of the anomaly, applying a local magnetic field parallel to an injected current induces a valley imbalance that diffuses over long distances. A probe magnetic field can then convert this imbalance into a measurable voltage drop far from source and drain. Such nonlocal transport vanishes when the injected current and magnetic field are orthogonal, and therefore serves as a test of the chiral anomaly. We further demonstrate that a similar effect should also characterize Dirac semimetals --- recently reported to have been observed in experiments --- where a pair of Weyl nodes coexisting at a single point in the Brillouin zone are protected by a crystal symmetry. Since the nodes are analogous to valley degrees of freedom in semiconductors, this suggests that valley currents in three dimensional topological semimetals can be controlled using electric fields, which has potential practical `valleytronic' applications.