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Edge conduction in monolayer WTe2

Nature Physics volume 13, pages 677–682 (2017)Cite this article

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Abstract

A two-dimensional topological insulator (2DTI) is guaranteed to have a helical one-dimensional edge mode1,2,3,4,5,6,7,8,9,10,11 in which spin is locked to momentum, producing the quantum spin Hall effect and prohibiting elastic backscattering at zero magnetic field. No monolayer material has yet been shown to be a 2DTI, but recently the Weyl semimetal WTe2 was predicted12 to become a 2DTI in monolayer form if a bulk gap opens. Here, we report that, at temperatures below about 100 K, monolayer WTe2 does become insulating in its interior, while the edges still conduct. The edge conduction is strongly suppressed by an in-plane magnetic field and is independent of gate voltage, save for mesoscopic fluctuations that grow on cooling due to a zero-bias anomaly, which reduces the linear-response conductance. Bilayer WTe2 also becomes insulating at low temperatures but does not show edge conduction. Many of these observations are consistent with monolayer WTe2 being a 2DTI. However, the low-temperature edge conductance, for contacts spacings down to 150 nm, never reaches values higher than ∼20 μS, about half the predicted value of e2/h, suggesting significant elastic scattering in the edge.

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Figure 1: Two-terminal characteristics of WTe2 devices.
Figure 2: Distinguishing edge and bulk conduction.
Figure 3: Temperature and magnetic field dependence of the edge conductance.
Figure 4: Statistics, nonlinear properties, and simple picture of edge conduction.

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Acknowledgements

We thank J. Yan (Oak Ridge National Laboratory) for providing the WTe2 crystals, and A. Andreev, L. Glazman, J. Maciejko, K. Matveev, J. Moore, B. Spivak, J. Väyrynen and D. Xiao for discussions. The major part of this work was supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, Awards DE-SC0002197 (D.H.C.) and DE-SC0012509 (X.X.). T.P. and Z.F. were supported by AFOSR FA9550-14-1-0277. P.N., J.F. and some facilities were supported by NSF EFRI 2DARE 1433496.

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Authors and Affiliations

  1. Department of Physics, University of Washington, Seattle, Washington 98195, USA

    Zaiyao Fei, Tauno Palomaki, Sanfeng Wu, Wenjin Zhao, Xinghan Cai, Bosong Sun, Paul Nguyen, Joseph Finney, Xiaodong Xu & David H. Cobden

  2. Department of Materials Science and Engineering, University of Washington, Seattle, Washington 98195, USA

    Xiaodong Xu

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  1. Zaiyao Fei
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Contributions

D.H.C. and X.X. conceived the experiment; Z.F., T.P., S.W. and D.H.C. performed the measurements; Z.F., W.Z., S.W., T.P., X.C., B.S., P.N. and J.F. fabricated the devices; D.H.C., X.X., Z.F. and T.P. analysed the results; and D.H.C., Z.F., T.P. and X.X. wrote the paper with comments from all authors.

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Correspondence to Xiaodong Xu or David H. Cobden.

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Fei, Z., Palomaki, T., Wu, S. et al. Edge conduction in monolayer WTe2. Nature Phys 13, 677–682 (2017). https://doi.org/10.1038/nphys4091

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