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Sign reversal of the order parameter in (Li1−xFex)OHFe1−yZnySe

Nature Physics volume 14, pages 134–139 (2018)Cite this article

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Abstract

Iron pnictides are the only known family of unconventional high-temperature superconductors besides cuprates. Until recently, it was widely accepted that superconductivity is driven by spin fluctuations and intimately related to the fermiology, specifically, hole and electron pockets separated by the same wavevector that characterizes the dominant spin fluctuations, and supporting order parameters (OP) of opposite signs1,2. This picture was questioned after the discovery of intercalated or monolayer form of FeSe-based systems without hole pockets, which seemingly undermines the basis for spin-fluctuation theory and the idea of a sign-changing OP3,4,5,6,7,8,9,10,11. Using the recently proposed phase-sensitive quasiparticle interference technique, here we show that in LiOH-intercalated FeSe compound the OP does change sign, albeit within the electronic pockets. This result unifies the pairing mechanism of iron-based superconductors with or without the hole Fermi pockets and supports the conclusion that spin fluctuations play the key role in electron pairing.

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Figure 1: In-gap resonant states of a non-magnetic impurity.
Figure 2: Quasiparticle interference around the single impurity.
Figure 3: Determination of sign reversal of the superconducting order parameter.

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Acknowledgements

We acknowledge the useful discussions with G. Kotliar, P. Coleman, D.-H. Lee and J. Zhao. The work in NJU was supported by National Key R&D Program of China (grant number: 2016YFA0300400), National Natural Science Foundation of China (NSFC) with the projects: A0402/11534005, A0402/11190023, A0402/11374144 and Natural Science Foundation of Jiangsu (grant number: BK20140015). P.J.H. was supported by NSF-DMR-1407502. I.I.M. was supported by ONR through the NRL Basic Research Program. D.A. and I.E. were supported by the joint DFG-ANR Project (ER 463/8-1) and DAAD PPP USA N57316180.

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Author notes

  1. Zengyi Du, Xiong Yang, Dustin Altenfeld, Qiangqiang Gu and Huan Yang: These authors contributed equally to this work.

Authors and Affiliations

  1. National Laboratory of Solid State Microstructures and Department of Physics, Center for Superconducting Physics and Materials, Collaborative Innovation Center for Advanced Microstructures, Nanjing University, Nanjing 210093, China

    Zengyi Du, Xiong Yang, Qiangqiang Gu, Huan Yang, Hai Lin, Xiyu Zhu & Hai-Hu Wen

  2. Institut für Theoretische Physik III, Ruhr-Universität Bochum, D-44801 Bochum, Germany

    Dustin Altenfeld & Ilya Eremin

  3. Department of Physics, University of Florida, Gainesville, Florida 32611, USA

    Peter J. Hirschfeld

  4. Code 6393, Naval Research Laboratory, Washington DC 20375, USA

    Igor I. Mazin

Authors
  1. Zengyi Du
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  2. Xiong Yang
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Contributions

The low-temperature STS measurements were performed by Z.D., X.Y., Q.G. and H.Y. Data analysis was done by Z.D., X.Y., Q.G., H.Y. and H.-H.W. The samples were grown by H.L. and X.Y.Z. The theoretical calculations were done by D.A. and I.E. All authors contributed to the writing of the paper, with P.H., I.I.M. and H.-H.W. responsible for the final text. H.-H.W. coordinated the whole work. All authors have discussed the results and the interpretations.

Corresponding authors

Correspondence to Peter J. Hirschfeld or Hai-Hu Wen.

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Du, Z., Yang, X., Altenfeld, D. et al. Sign reversal of the order parameter in (Li1−xFex)OHFe1−yZnySe. Nat. Phys. 14, 134–139 (2018). https://doi.org/10.1038/nphys4299

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