Directional massless Dirac fermions in a layered van der Waals material with one-dimensional long-range order

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Abstract

One or a few layers of van der Waals (vdW) materials are promising for applications in nanoscale electronics. Established properties include high mobility in graphene, a large direct gap in monolayer MoS2, the quantum spin Hall effect in monolayer WTe2 and so on. These exciting properties arise from electron quantum confinement in the two-dimensional limit. Here, we use angle-resolved photoemission spectroscopy to reveal directional massless Dirac fermions due to one-dimensional confinement of carriers in the layered vdW material NbSi0.45Te2. The one-dimensional directional massless Dirac fermions are protected by non-symmorphic symmetry, and emerge from a stripe-like structural modulation with long-range translational symmetry only along the stripe direction as we show using scanning tunnelling microscopy. Our work not only provides a playground for investigating further the properties of directional massless Dirac fermions, but also introduces a unique component with one-dimensional long-range order for engineering nano-electronic devices based on heterostructures of vdW materials.

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Fig. 1: Crystal structure and core-level spectra of NbSixTe2.
Fig. 2: Surface electronic structure of NbSi0.45Te2.
Fig. 3: 1D Dirac dispersion on the stripe-like surface of NbSi0.45Te2.
Fig. 4: The non-symmorphic symmetry protected 1D Dirac dispersion with fourfold degeneracy.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.

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Acknowledgements

This work was supported by the National Key R&D Programme of China (grant nos. 2018FYA0305800, 2016YFA0300403 and 2017YFA0302901), the Ministry of Science and Technology of China (grant no. 2018YFA0307000), the National Natural Science Foundation of China (grant nos. 11874047, 11674226, 11790313 and 11774399), the Fundamental Research Funds for the Central Universities (grant no. 2042018kf-0030), Beijing Natural Science Foundation (grant no. Z180008) and the K. C. Wong Education Foundation (grant no. GJTD-2018-01). Z.Q.M. acknowledges the support by the US Department of Energy under grant no. DE-SC0019068. N.X. acknowledges support by Wuhan University startup funding.

Author information

N.X. conceived the experiments. T.Y.Y, Q.W., C.P. and N.X. performed the ARPES measurements with the assistance of Y.B.H. D.Y.Y and Y.G.S. synthesized the NbSi0.45Te2 single crystals. Z.Z, H.Z. and J.-F.J. performed the STM measurements. Z.W.W, R.Y., S.L., S.A.Y. performed the ab initio calculations. J.H. and Z.Q.M synthesized the NbSi1/3Te2 single crystals as reference samples. T.Y.Y, Q.W., H.Z. and N.X. analysed the experimental data. N.X. wrote the manuscript. All authors discussed the results and commented on the manuscript.

Correspondence to N. Xu.

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Supplementary Figs. 1–6.

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