Recently, a type-II Weyl fermion was theoretically predicted to appear at the contact of electron and hole Fermi surface pockets. A distinguishing feature of the surfaces of type-II Weyl semimetals is the existence of topological surface states, so-called Fermi arcs. Although WTe2 was the first material suggested as a type-II Weyl semimetal, the direct observation of its tilting Weyl cone and Fermi arc has not yet been successful. Here, we show strong evidence that WTe2 is a type-II Weyl semimetal by observing two unique transport properties simultaneously in one WTe2 nanoribbon. The negative magnetoresistance induced by a chiral anomaly is quite anisotropic in WTe2 nanoribbons, which is present in b-axis ribbon, but is absent in a-axis ribbon. An extra-quantum oscillation, arising from a Weyl orbit formed by the Fermi arc and bulk Landau levels, displays a two dimensional feature and decays as the thickness increases in WTe2 nanoribbon.
Bibliographical noteFunding Information:
We’d like to thank Prof. Xi Dai, institute of Physics (Beijing), for his critical reading and useful discussion in the revision of the manuscript. We thank Y. Yang for the assistance on polarized Raman, and Z. P. Hou for the useful discussion. The research reported in this publication was supported by funding from King Abdullah University of Science and Technology (KAUST). P.L. acknowledges the financial support of CRF-2015-SENSORS-2709 (KAUST).
© 2017 The Author(s).
ASJC Scopus subject areas
- Physics and Astronomy(all)
- Biochemistry, Genetics and Molecular Biology(all)