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Weyl points and Fermi arcs in a chiral phononic crystal

Nature Physics volume 14, pages 30–34 (2018)Cite this article

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Abstract

Topological semimetals are materials whose band structure contains touching points that are topologically nontrivial and can host quasiparticle excitations that behave as Dirac or Weyl fermions1,2,3,4,5,6,7. These so-called Weyl points not only exist in electronic systems, but can also be found in artificial periodic structures with classical waves, such as electromagnetic waves in photonic crystals8,9,10,11 and acoustic waves in phononic crystals12,13. Due to the lack of spin and a difficulty in breaking time-reversal symmetry for sound, however, topological acoustic materials cannot be achieved in the same way as electronic or optical systems. And despite many theoretical predictions12,13, experimentally realizing Weyl points in phononic crystals remains challenging. Here, we experimentally realize Weyl points in a chiral phononic crystal system, and demonstrate surface states associated with the Weyl points that are topological in nature, and can host modes that propagate only in one direction. As with their photonic counterparts, chiral phononic crystals bring topological physics to the macroscopic scale.

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Figure 1: Illustration of the unit cell of the phononic crystal.
Figure 2: Bulk bands of the two lowest modes.
Figure 3: Surface waves and the dispersions.
Figure 4: Experimental one-way propagation of surface states in the presence of a defect.

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Acknowledgements

This work is supported by the National Basic Research Program of China (Grant No. 2015CB755500), the National Natural Science Foundation of China (Grant Nos 61271139, 11572318, 11604102, and 11374233), Guangdong Innovative and Entrepreneurial Research Team Program (Grant No. 2016ZT06C594) and the National Postdoctoral Program for Innovative Talents (BX201600054).

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Author notes

  1. Feng Li and Xueqin Huang: These authors contributed equally to this work.

Authors and Affiliations

  1. School of Physics and Optoelectronic Technology, South China University of Technology, Guangzhou, Guangdong 510640, China

    Feng Li, Xueqin Huang, Jiuyang Lu & Jiahong Ma

  2. Key Laboratory of Artificial Micro- and Nanostructures of Ministry of Education and School of Physics and Technology, Wuhan University, Wuhan 430072, China

    Zhengyou Liu

  3. Institute for Advanced Studies, Wuhan University, Wuhan 430072, China

    Zhengyou Liu

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  1. Feng Li
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Contributions

Z.L. initiated and supervised the project. F.L. designed and performed the experiments. X.Q.H. and J.Y.L. carried out the numerical simulations. Z.L., F.L., X.Q.H. and J.Y.L. wrote the manuscript. All authors contributed to the analyses and discussions of the manuscript.

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Correspondence to Zhengyou Liu.

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The authors declare no competing financial interests.

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Li, F., Huang, X., Lu, J. et al. Weyl points and Fermi arcs in a chiral phononic crystal. Nature Phys 14, 30–34 (2018). https://doi.org/10.1038/nphys4275

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