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Surface morphology and electronic structure in stoichiometric superconductor CaKFe4As4 probed by scanning tunneling microscopy/spectroscopy

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Abstract

CaKFe4As4 is a new-type superconductor with a relatively high transition temperature of 35 K among stoichiometric iron-based superconductors. Based on scanning tunneling microscopy/spectroscopy, the surface morphology and electronic structure of CaKFe4As4 single crystal were systematically investigated. The cleaved CaKFe4As4 showed various morphologies, such as atomically resolved 1×1, 1×2, and \(\sqrt 2 \times \sqrt 2 \) lattices. By analyzing the geometrical correlations of these morphologies, the 1×1 and 1×2 lattices were identified as the original and reconstructed As layers, respectively, whereas the \(\sqrt 2 \times \sqrt 2 \) lattice was distinguished as the reconstructed alkaline-earth-metal or alkali-metal layer. The superconducting energy gap of 7.3 meV and bosonic mode of 12.7 meV were resolved in the scanning tunneling spectra. In addition, the superconducting energy gaps measured on different terminations were identical and consistent with the values obtained by bulk-sensitive techniques, indicating that the electronic structures of CaKFe4As4 were insensitive to the surface reconstructions. Our study clarifies the relationships between complex surface reconstructions and surface terminations and preliminarily presents that there is no obvious effect of surface reconstructions on electronic states.

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Authors and Affiliations

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

    Xiaodong Yu, Zhongxu Wei, Zhanyi Zhao, Tao Xie, Chang Liu, Qihong Chen, Huiqian Luo, Qing Huan, Jie Yuan & Kui Jin

  2. School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China

    Xiaodong Yu, Zhongxu Wei, Zhanyi Zhao, Tao Xie, Chang Liu, Qihong Chen & Kui Jin

  3. Walther Meissner Institute, Bayerische Akademie der Wissenschaften, Garching, 85748, Germany

    Ge He

  4. Key Laboratory of Structure and Functional Regulation of Hybrid Materials of Ministry of Education, Institutes of Physical Science and Information Technology, Anhui University, Hefei, 230601, China

    Lei Shan

  5. Songshan Lake Materials Laboratory, Dongguan, 523808, China

    Huiqian Luo, Qing Huan, Jie Yuan & Kui Jin

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  1. Xiaodong Yu
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Correspondence to Zhongxu Wei.

Additional information

This work was supported by the National Key Basic Research Program of China (Grant Nos. 2017YFA0302902, 2016YFA0300301, 2017YFA0303003, and 2018YFB0704102), the National Natural Science Foundation of China (Grant Nos. 11927808, 11834016, 118115301, 119611410, 11961141008, 11822411, and 11961160699), the Key Research Program of Frontier Sciences, Chinese Academy of Sciences (Grant Nos. QYZDBSSW-SLH008, and QYZDY-SSW-SLH001), the Strategic Priority Research Program (B) of Chinese Academy of Sciences (Grant Nos. XDB25000000, and XDB33000000), the Beijing Natural Science Foundation (Grant Nos. Z190008, and JQ19002), the Key-Area Research and Development Program of Guangdong Province (Grant No. 2020B0101340002), and the CAS Interdisciplinary Innovation Team. H. Luo is grateful for the support from the Youth Innovation Promotion Association of CAS (Grant No. Y202001).

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Yu, X., Wei, Z., Zhao, Z. et al. Surface morphology and electronic structure in stoichiometric superconductor CaKFe4As4 probed by scanning tunneling microscopy/spectroscopy. Sci. China Phys. Mech. Astron. 64, 127411 (2021). https://doi.org/10.1007/s11433-021-1804-7

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