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 the application of parallel electric (E) and magnetic (B) fields pumps electrons between nodes of opposite chirality at a rate proportional to E·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 the coexistence of a pair of Weyl nodes at a single point in the Brillouin zone is protected by a crystal symmetry. Since the nodes are analogous to valley degrees of freedom in semiconductors, the existence of the anomaly suggests that valley currents in three-dimensional topological semimetals can be controlled using electric fields, which has potential practical “valleytronic” applications.Received 14 September 2013DOI:https://doi.org/10.1103/PhysRevX.4.031035This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical Society
Highlights
Weyl semimetals (WSMs) are three-dimensional analogs of graphene that have received much attention following a recent proposal that they may occur in a class of iridate materials [1]
We further demonstrate that a similar effect should characterize Dirac semimetals—recently reported to have been observed in experiments—where the coexistence of a pair of Weyl nodes at a single point in the Brillouin zone is protected by a crystal symmetry
We have suggested a route to studying the chiral anomaly in three-dimensional topological semimetals by using it to produce and detect valley imbalance and using the slow relaxation of the latter to produce nonlocal voltage drops, which can be distinguished from more conventional Ohmic effects
Summary
Weyl semimetals (WSMs) are three-dimensional analogs of graphene that have received much attention following a recent proposal that they may occur in a class of iridate materials [1]. Related to the WSM is the Dirac semimetal (DSM) [7,8,9], where a pair of Weyl nodes of opposite chirality coexists at a point in the three-dimensional Brillouin zone— and four bands touch, rather than two Naively, it appears that this situation would be unstable against a variety of gap-opening scenarios, in certain cases, the resulting gapped phases always break a crystalline pointgroup symmetry. Existing approaches to study the topological response of WSMs stand in marked contrast to the simple transport experiment proposed here, which applies generally to all realizations of WSMs and satisfies the criteria outlined earlier: Namely, it involves a signal that is absent for conventional (semi)metals and can be ascribed to the presence of an E · B term by examining its dependence on the orientation of the magnetic field. We conclude with a discussion of our results and possible extensions
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
