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Observation of a robust zero-energy bound state in iron-based superconductor Fe(Te,Se)

Nature Physics volume 11, pages 543546 (2015) | Download Citation


In superconductors, electrons are paired and condensed into the ground state. An impurity can break the electron pairs into quasiparticles with energy states inside the superconducting gap. The characteristics of such in-gap states reflect accordingly the properties of the superconducting ground state1. A zero-energy in-gap state is particularly noteworthy, because it can be the consequence of non-trivial pairing symmetry1 or topology2,3. Here we use scanning tunnelling microscopy/spectroscopy to demonstrate that an isotropic zero-energy bound state with a decay length of 10 Å emerges at each interstitial iron impurity in superconducting Fe(Te,Se). More noticeably, this zero-energy bound state is robust against a magnetic field up to 8 T, as well as perturbations by neighbouring impurities. Such a spectroscopic feature has no natural explanation in terms of impurity states in superconductors with s-wave symmetry, but bears all the characteristics of the Majorana bound state proposed for topological superconductors2,3, indicating that the superconducting state and the scattering mechanism of the interstitial iron impurities in Fe(Te,Se) are highly unconventional.

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The authors thank Z. Fang, X. Dai, T. Xiang, D-H. Lee, T-K. Lee, G-M. Zhang and P. Coleman for stimulating discussions. This work is supported by the State of Texas through TcSUH, the Chinese Academy of Sciences, US Air Force Office of Scientific Research (FA9550-09-1-0656), Robert A. Welch Foundation (E-1146), US DOE (DE-SC0002554, DE-FG02-99ER45747), National Science Foundation of China (11322432, 11190020), and Ministry of Science and Technology of China (2012CB933000).

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Author notes

    • J-X. Yin
    •  & Zheng Wu

    These authors contributed equally to this work.


  1. Beijing National Laboratory for Condensed Matter Physics, and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China

    • J-X. Yin
    • , Z-Y. Ye
    • , Jing Gong
    • , X-Y. Hou
    • , Lei Shan
    • , X-J. Liang
    • , X-X. Wu
    • , J-P. Hu
    • , H. Ding
    •  & S. H. Pan
  2. Department of Physics and Texas Center for Superconductivity, University of Houston, Houston, Texas 77204, USA

    • J-X. Yin
    • , Zheng Wu
    • , J-H. Wang
    • , Z-Y. Ye
    • , Ang Li
    • , Jian Li
    • , C-S. Ting
    • , P-H. Hor
    •  & S. H. Pan
  3. Collaborative Innovation Center of Quantum Matter, Beijing 100190, China

    • Lei Shan
    • , H. Ding
    •  & S. H. Pan
  4. Department of Physics, Boston College, Chestnut Hill, Massachusetts 02467, USA

    • Z-Q. Wang
  5. Department of Physics, Purdue University, West Lafayette, Indiana 47907, USA

    • J-P. Hu


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J-X.Y. carried out the STM/S experiments with contributions from Z.W., J-H.W., Z-Y.Y., J.G., X-Y.H., L.S., A.L. and X-J.L.; Z.W. synthesized and characterized the sequence of samples; J-X.Y., S.H.P. and H.D. performed the data analysis, figure development and wrote the paper with contributions from J-P.H., Z-Q.W., C-S.T., P-H.H., J.L. and X-X.W.; S.H.P. supervised the project. All authors discussed the results and the interpretation.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to S. H. Pan.

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