Bilayer Spliting and Unusual Superconducting Gap in KCa<sub>2</sub>Fe<sub>4</sub>As<sub>4</sub>F<sub>2</sub> Superconductor with Double Fe<sub>2</sub>As<sub>2</sub> Layers

ORAL

Abstract

We report the first high resolution laser Angle-Resolved Photoemission Spectroscopy(ARPES) measurements on a newly discovered iron based superconductor, KCa2Fe4As4F2 (K12442) which has the K+-cations connecting double Fe2As2 layers separated by the insulating Ca2F2 block with a high TC of 34 K at stoichiometric composition. Total five hole like Fermi surfaces are clearly identified around Brillouin zone center Γ(0,0) point and four of them are possible from the bilayer splitting of two Fermi surfaces. A tiny electron like pocket is shown around M(±π,±π) points surrounded by four strong spots with their top just below Fermi level. All the hole like pockets around Γ(0,0) point exhibit nearly isotropic nodeless superconducting gap symmetry but with different gap sizes. Their gap sizes can neither be understood in the simple │cos(kx)+cos(ky)│ functional form due to the biggest gap size from one middle Fermi surface, nor be consistent with the so-called quasi-nesting between the Fermi pockets around Γ and M points because of mismatch of Femri pocket size. Our observations provide new information and require new insight to understand the superconductivity mechanism in iron based superconductor.

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Presenters

  • Dingsong Wu

    • Chinese Academy of Sciences,Institute of Physics
    • Institute of Physics, Chinese Academy of Science,Beijing 100190, China

Authors

  • Dingsong Wu

    • Chinese Academy of Sciences,Institute of Physics
    • Institute of Physics, Chinese Academy of Science,Beijing 100190, China

  • Wenshan Hong

    • Institute of Physics, Chinese Academy of Science,Beijing 100190, China

  • Chengxiao Dong

    • Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences
    • Institute of Physics, Chinese Academy of Science,Beijing 100190, China

  • Jiangping Hu

    • Chinese Academy of Sciences,Institute of Physics
    • Institute of Physics, Chinese Academy of Sciences
    • Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences
    • Institute of Physics, Chinese Academy of Science,Beijing 100190, China
    • Beijing National Research Center for Condensed Matter Physics, and Institute of Physics, Chinese Academy of Sciences
    • Institute of Physics, Chinese Academy of Science

  • Shiliang Li

    • Institute of Physics, Chinese Academy of Science,Beijing 100190, China

  • Huiqian Luo

    • Institute of Physics, Chinese Academy of Science,Beijing 100190, China

  • Lin Zhao

    • Chinese Academy of Sciences,Institute of Physics
    • Institute of Physics, Chinese Academy of Science,Beijing 100190, China
    • Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences

  • Xingjiang Zhou

    • Beijing National Laboratory for Condensed Matter Physics, Insititute of Physics, Chinese Academy of Science
    • Institute of Physics, Chinese Academy of Science,Beijing 100190, China
    • Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences