Abstract

Weyl semimetal is a new quantum state of matter1,2,3,4,5,6,7,8,9,10,11,12 hosting the condensed matter physics counterpart of the relativistic Weyl fermions13 originally introduced in high-energy physics. The Weyl semimetal phase realized in the TaAs class of materials features multiple Fermi arcs arising from topological surface states10,11,14,15,16 and exhibits novel quantum phenomena, such as a chiral anomaly-induced negative magnetoresistance17,18,19 and possibly emergent supersymmetry20. Recently it was proposed theoretically that a new type (type-II) of Weyl fermion21,22 that arises due to the breaking of Lorentz invariance, which does not have a counterpart in high-energy physics, can emerge as topologically protected touching between electron and hole pockets. Here, we report direct experimental evidence of topological Fermi arcs in the predicted type-II Weyl semimetal MoTe2 (refs 23,24,25). The topological surface states are confirmed by directly observing the surface states using bulk- and surface-sensitive angle-resolved photoemission spectroscopy, and the quasi-particle interference pattern between the putative topological Fermi arcs in scanning tunnelling microscopy. By establishing MoTe2 as an experimental realization of a type-II Weyl semimetal, our work opens up opportunities for probing the physical properties of this exciting new state.

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Acknowledgements

This work is supported by the National Natural Science Foundation of China (grant no. 11274191, 11334006), Ministry of Science and Technology of China (no. 2015CB92100, 2016YFA0301004 and 2012CB932301) and Tsinghua University Initiative Scientific Research Program (no. 2012Z02285). The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under contract no. DE-AC02-05CH11231.

Author information

Author notes

    • Ke Deng
    • , Guoliang Wan
    •  & Peng Deng

    These authors contributed equally to this work.

Affiliations

  1. State Key Laboratory of Low Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, China

    • Ke Deng
    • , Guoliang Wan
    • , Peng Deng
    • , Kenan Zhang
    • , Shijie Ding
    • , Eryin Wang
    • , Mingzhe Yan
    • , Huaqing Huang
    • , Hongyun Zhang
    • , Zhilin Xu
    • , Haitao Yang
    • , Wenhui Duan
    • , Shoushan Fan
    • , Xi Chen
    •  & Shuyun Zhou
  2. Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

    • Jonathan Denlinger
    •  & Alexei Fedorov
  3. Tsinghua-Foxconn Nanotechnology Research Center, Tsinghua University, Beijing 100084, China

    • Haitao Yang
    • , Yang Wu
    •  & Shoushan Fan
  4. Collaborative Innovation Center of Quantum Matter, Beijing, China

    • Wenhui Duan
    • , Hong Yao
    • , Shoushan Fan
    • , Xi Chen
    •  & Shuyun Zhou
  5. Institute for Advanced Study, Tsinghua University, Beijing 100084, China

    • Hong Yao
  6. National Laboratory of Solid State Microstructures and School of Physics, Nanjing University, Nanjing 210093, China

    • Haijun Zhang
  7. Collaborative Innovation Center of Advanced Microstructures, Nanjing, China

    • Haijun Zhang

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Contributions

S.Z., X.C. and Y.W. conceived the research project. K.D. and K.Z. grew and characterized the samples under the supervision of Y.W. K.D., G.W., K.Z., S.D., E.W., M.Y. and Hongyun Z. performed the ARPES measurements and analysed the ARPES data. J.D. and A.F. provided support for the ARPES experiments. P.D. and Z.X. performed the STM measurements. Haijun Z. performed the first-principles calculations presented in the manuscript. H.H. and W.D. repeated the calculation. K.D., H.Yao, Y.W., X.C. and S.Z. wrote the manuscript, and all authors commented on the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to Yang Wu or Xi Chen or Shuyun Zhou.

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DOI

https://doi.org/10.1038/nphys3871

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