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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The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.
Novoselov, K. S. et al. Electric field effect in atomically thin carbon films. Science 306, 666–669 (2004).
Mak, K. F., Lee, C., Hone, J., Shan, J. & Heinz, T. F. Atomically thin MoS2: a new direct-gap semiconductor. Phys. Rev. Lett. 105, 136805 (2010).
Lu, J. M. et al. Evidence for two-dimensional Ising superconductivity in gated MoS2. Science 350, 1353–1357 (2015).
Xi, X. X. et al. Ising pairing in superconducting NbSe2 atomic layers. Nat. Phys. 12, 139–143 (2016).
Qian, X. F., Liu, J. W., Fu, L. & Li, J. Quantum spin Hall effect in two-dimensional transition metal dichalcogenides. Science 346, 1344–1347 (2014).
Fei, Z. Y. et al. Edge conduction in monolayer WTe2. Nat. Phys. 13, 677–682 (2017).
Tang, S. J. et al. Quantum spin hall state in monolayer 1T’-WTe2. Nat. Phys. 13, 683–687 (2017).
Wu, S. F. et al. Observation of the quantum spin hall effect up to 100 kelvin in a monolayer crystal. Science 359, 76–79 (2018).
Zhu, Z. et al. Quasiparticle interference and nonsymmorphic effect on a floating band surface state of ZrSiSe. Nat. Commum. 9, 4153 (2018).
Gong, C. et al. Discovery of intrinsic ferromagnetism in two-dimensional van der Waals crystals. Nature 546, 265–269 (2017).
Huang, B. et al. Layer-dependent ferromagnetism in a van der Waals crystal down to the monolayer limit. Nature 546, 270–273 (2017).
Cao, Y. et al. Unconventional superconductivity in magic-angle graphene superlattices. Nature 556, 43–50 (2018).
Cao, Y. et al. Correlated insulator behaviour at half-filling in magic angle graphene superlattices. Nature 556, 80–84 (2018).
Young, S. M. & Kane, C. L. Dirac semimetals in two dimensions. Phys. Rev. Lett. 115, 126803 (2015).
Bzdušek, T., Wu, Q., Rüegg, A., Sigrist, M. & Soluyanov, A. A. Nodal-chain metals. Nature 538, 75–78 (2016).
Wang, Z. et al. Dirac semimetal and topological phase transitions in A3Bi (A = Na, K, Rb). Phys. Rev. B 85, 195320 (2012).
Li, J., Badding, M. E. & DiSalvo, F. J. New layered ternary niobium tellurides: synthesis, structure, and properties of niobium metal telluride. NbMTe2 (M = iron, cobalt). Inorg. Chem. 31, 1050–1054 (1992).
Huang, B., Shang, B. & Huang, J. Crystal structure of mixed metal cluster Co2Nb2Te4 obtained by solid state reaction. Jiegou Huaxue (J. Struct. Chem.) 7, 133 (1988).
Huang, B., Shang, B. & Huang, J. Crystal structure of mixed metal cluster Ni2Nb2Te4 obtained by solid state reaction. Jiegou Huaxue (J. Struct. Chem.) 7, 214 (1988).
Huang, B., Shang, B. & Huang, J. Synthesis and crystal structure of a new ternary tantalum chalcogenide Ni2Ta2Te4. Jiegou Huaxue (J. Struct. Chem.) 8, 145 (1989).
Li, J., Badding, M. E. & DiSalvo, F. J. Synthesis and structure of Nb3SiTe6, a new layered ternary niobium telluride compound. J. Alloy. Compd. 184, 257–163 (1992).
Hu, J. et al. Enhanced electron coherence in atomically thin Nb3SiTe6. Nat. Phys. 11, 471–476 (2015).
Li, Si et al. Nonsymmorphic-symmetry-protected hourglass dirac loop, nodal line, and dirac point in bulk and monolayer X3SiTe6 (X = Ta, Nb). Phys. Rev. B 97, 045131 (2018).
Boucher, F., Zhukov, V. & Evain, M. MAxTe2 phases (M = Nb, Ta; A = Si, Ge; 1/3 ≤ x ≤ 1/2): an electronic band structure calculation analysis. Chem. 35, 7649–7654 (1996).
Weber, F. et al. Three-dimensional Fermi surface of 2H-NbSe2: implications for the mechanism of charge density waves. Phys. Rev. B 97, 235122 (2018).
Sato, T. et al. Observation of band crossings protected by nonsymmorphic symmetry in the layered ternary telluride Ta3SiTe6. Phys. Rev. B 98, 121111(R) (2018).
Riley, J. M. et al. Direct observation of spin-polarized bulk bands in an inversion-symmetric semiconductor. Nat. Phys. 10, 835–839 (2014).
Pescia, D., Law, A. R., Johnson, M. T. & Hughes, H. P. Determination of observable conduction band symmetry in angle-resolved electron spectroscopies: Non-symmorphic space groups. Solid State Commun. 56, 809–812 (1985).
Finteis, Th et al. Occupied and unoccupied electronic band structure of WSe2. Phys. Rev. B 55, 10400 (1997).
Landolt, G. et al. Bulk and surface rashba splitting in single termination BiTeCl. New J. Phys. 15, 085022 (2013).
Koller, G. et al. Intra- and intermolecular band dispersion in an organic crystal. Science 317, 351–355 (2007).
Yin, D., Chen, C., Saito, M., Inoue, K. & Ikuhara, Y. Ceramic phases with one-dimensional long-range order. Nat. Mater. 18, 19–23 (2019).
Liu, Z. K. et al. Discovery of a three-dimensional topological dirac semimetal, Na3Bi. Science 343, 864–867 (2014).
Neupane, M. et al. Observation of a three-dimensional topological dirac semimetal phase in high-mobility Cd3As2. Nat. Commun. 5, 3786 (2014).
Borisenko, S. et al. Experimental realization of a three-dimensional dirac semimetal. Phys. Rev. Lett. 113, 027603 (2014).
Schoop, L. M. et al. Dirac cone protected by non-symmorphic symmetry and three-dimensional dirac line node in ZrSiS. Nat. Commun. 7, 11696 (2016).
Ekahana, S. A. et al. Observation of nodal line in non-symmorphic topological semimetal InBi. New J. Phys. 19, 065007 (2017).
Schoop, L. M. et al. Tunable weyl and dirac states in the nonsymmorphic compound CeSbTe. Sci. Adv. 4, eaar2317 (2018).
Nakayama, K. et al. Band splitting and weyl nodes in trigonal tellurium studied by angle-resolved photoemission spectroscopy and density functional theory. Phys. Rev. B 95, 125204 (2017).
Weng, H. et al. Topological node-line semimetal in three-dimensional graphene networks. Phys. Rev. B 92, 045108 (2015).
Bian, G. et al. Topological nodal-line fermions in spin-orbit metal PbTaSe2. Nat. Commun. 7, 10556 (2016).
Hu, J. et al. Evidence of topological nodal-line fermions in ZrSiSe and ZrSiTe. Phys. Rev. Lett. 117, 016602 (2016).
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.
The authors declare no competing interests.
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