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Research Article

The As-surface of an iron-based superconductor CaKFe4As4

Lu Cao1,2,§, Yang Song1,2,§, Ya-Bin Liu5, Qi Zheng1,2, Guangyuan Han1,2, Wenyao Liu1,2, Meng Li1,2, Hui Chen1,2, Yuqing Xing1,2, Guang-Han Cao5, Hong Ding1,3,4, Xiao Lin1,2,3, Shixuan Du1,2,3,4( ), Yu-Yang Zhang1,2,3, Geng Li1,2,3,4( ), Ziqiang Wang6, Hong-Jun Gao1,2,3,4( )
Institute of Physics Chinese Academy of SciencesBeijing 100190 China
School of Physical Sciences University of Chinese Academy of SciencesBeijing 100049 China
CAS Center for Excellence in Topological Quantum Computation University of Chinese Academy of SciencesBeijing 100190 China
Songshan Lake Materials Laboratory Dongguan 523808 China
Department of Physics Zhejiang UniversityHangzhou 310027 China
Department of Physics Boston College, Chestnut HillMassachusetts 02467 USA

§Lu Cao and Yang Song contributed equally to this work.

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Graphical Abstract

Abstract

As a new type of iron-based superconductor, CaKFe4As4 has recently been demonstrated to be a promising platform for observing Majorana zero modes (MZMs). The surface of CaKFe4As4 plays an important role in realizing the MZM since it hosts superconducting topological surface states. However, due to the complicated crystal structure, the terminal surface of CaKFe4As4 has not been determined yet. Here, by using scanning tunneling microscopy/spectroscopy (STM/S), we find that there are two types of surface structure in CaKFe4As4. Bias-dependent atomic resolution images show an evolvement from 2 × 2 superstructure with respect to the As lattice into 1 × 1 when the tip is brought close to the surface, revealing the sublattice of missing As atoms. Together with the first-principles calculations, we show that the surface As layer has a buckled structure. Our findings provide insight to future surface study of CaKFe4As4 as well as other iron-pnictide superconductors.

Keywords

CaKFe4As4scanning tunneling microscopyatomic resolutiondensity functional theory

References

1

Kamihara, Y.; Watanabe, T.; Hirano, M.; Hosono, H. Iron-based layered superconductor La[O1-xFx]FeAs (x = 0.05-0.12) with Tc = 26 K. J. Am. Chem. Soc. 2008, 130, 3296-3297.
Crossref Google Scholar
2

Paglione, J.; Greene, R. L. High-temperature superconductivity in iron-based materials. Nat. Phys. 2010, 6, 645-658.
Crossref Google Scholar
3

Hirschfeld, P. J.; Korshunov, M. M.; Mazin, I. I. Gap symmetry and structure of Fe-based superconductors. Rep. Prog. Phys. 2011, 74, 124508.
Crossref Google Scholar
4

Stewart, G. R. Superconductivity in iron compounds. Rev. Mod. Phys. 2011, 83, 1589-1652.
Crossref Google Scholar
5

Wang, F.; Lee, D. H. The electron-pairing mechanism of iron-based superconductors. Science 2011, 332, 200-204.
Crossref Google Scholar
6

Kordyuk, A. A. Iron-based superconductors: Magnetism, superconductivity, and electronic structure (Review Article). Low Temp. Phys. 2012, 38, 888-899.
Crossref Google Scholar
7

Chen, X. H.; Dai, P. C.; Feng, D. L.; Xiang, T.; Zhang, F. C. Iron-based high transition temperature superconductors. Natl. Sci. Rev. 2014, 1, 371-395.
Crossref Google Scholar
8

Si, Q. M.; Yu, R.; Abrahams, E. High-temperature superconductivity in iron pnictides and chalcogenides. Nat. Rev. Mater. 2016, 1, 16017.
Crossref Google Scholar
9

Hoffman, J. E. Spectroscopic scanning tunneling microscopy insights into Fe-based superconductors. Rep. Prog. Phys. 2011, 74, 124513.
Crossref Google Scholar
10

Richard, P.; Sato, T.; Nakayama, K.; Takahashi, T.; Ding, H. Fe-based superconductors: An angle-resolved photoemission spectroscopy perspective. Rep. Prog. Phys. 2011, 74, 124512.
Crossref Google Scholar
11

Liu, W. Y.; Cao, L.; Zhu, S. Y.; Kong, L. Y.; Wang, G. W.; Papaj, M.; Zhang, P.; Liu, Y. B.; Chen, H.; Li, G. et al. A new Majorana platform in an Fe-As bilayer superconductor. Nat. Commun. 2020, 11, 5688.
Crossref Google Scholar
12

Zhang, P.; Yaji, K.; Hashimoto, T.; Ota, Y.; Kondo, T.; Okazaki, K.; Wang, Z. J.; Wen, J. S.; Gu, G. D.; Ding, H. et al. Observation of topological superconductivity on the surface of an iron-based superconductor. Science 2018, 360, 182-186.
Crossref Google Scholar
13

Wang, D. F.; Kong, L. Y.; Fan, P.; Chen, H.; Zhu, S. Y.; Liu, W. Y.; Cao, L.; Sun, Y. J.; Du, S. X.; Schneeloch, J. et al. Evidence for Majorana bound states in an iron-based superconductor. Science 2018, 362, 333-335.
Crossref Google Scholar
14

Kong, L. Y.; Zhu, S. Y.; Papaj, M.; Chen, H.; Cao, L.; Isobe, H.; Xing, Y. Q.; Liu, W. Y.; Wang, D. F.; Fan, P. et al. Half-integer level shift of vortex bound states in an iron-based superconductor. Nat. Phys. 2019, 15, 1181-1187.
Crossref Google Scholar
15

Zhu, S. Y.; Kong, L. Y.; Cao, L.; Chen, H.; Papaj, M.; Du, S. X.; Xing, Y. Q.; Liu, W. Y.; Wang, D. F.; Shen, C. M. et al. Nearly quantized conductance plateau of vortex zero mode in an iron-based superconductor. Science 2020, 367, 189-192.
Crossref Google Scholar
16

Shan, L.; Wang, Y. L.; Shen, B.; Zeng, B.; Huang, Y.; Li, A.; Wang, D.; Yang, H.; Ren, C.; Wang, Q. H. et al. Observation of ordered vortices with Andreev bound states in Ba0.6K0.4Fe2As2. Nat. Phys. 2011, 7, 325-331.
Crossref Google Scholar
17

Li, A.; Yin, J. X.; Wang, J. H.; Wu, Z.; Ma, J. H.; Sefat, A. S.; Sales, B. C.; Mandrus, D. G.; McGuire, M. A.; Jin, R. Y. et al. Surface terminations and layer-resolved tunneling spectroscopy of the 122 iron pnictide superconductors. Phys. Rev. B 2019, 99, 134520.
Crossref Google Scholar
18

Massee, F.; de Jong, S.; Huang, Y.; Kaas, J.; van Heumen, E.; Goedkoop, J. B.; Golden, M. S. Cleavage surfaces of the BaFe2-xCoxAs2 and FeySe1-xTex superconductors: A combined STM plus LEED study. Phys. Rev. B 2009, 80, 140507(R).
Crossref Google Scholar
19

Nascimento, V. B.; Li, A.; Jayasundara, D. R.; Xuan, Y.; O'Neal, J.; Pan, S. H.; Chien, T. Y.; Hu, B.; He, X. B.; Li, G. R. et al. Surface geometric and electronic structures of BaFe2As2(001). Phys. Rev. Lett. 2009, 103, 076104.
Crossref Google Scholar
20

Zhang, H.; Dai, J.; Zhang, Y. J.; Qu, D. R.; Ji, H. W.; Wu, G.; Wang, X. F.; Chen, X. H.; Wang, B.; Zeng, C. G. et al. 2×2 structure and charge inhomogeneity at the surface of superconducting BaFe2-xCoxAs2 (x = 0-0.32). Phys. Rev. B 2010, 81, 104520.
Crossref Google Scholar
21

Nishizaki, T.; Nakajima, Y.; Tamegai, T.; Kobayashi, N. Surface structure and superconductivity in Ba(Fe0.93Co0.07)2As2 probed by scanning tunneling microscopy/spectroscopy. J. Phys. Soc. Jpn. 2011, 80, 014710.
Crossref Google Scholar
22

Li, G. R.; He, X. B.; Zhang, J. D.; Jin, R. Y.; Sefat, A. S.; McGuire, M. A.; Mandrus, D. G.; Sales, B. C.; Plummer, E. W. Coupled structural and magnetic antiphase domain walls on BaFe2As2. Phys. Rev. B 2012, 86, 060512(R).
Crossref Google Scholar
23

Fang, D. L.; Shi, X.; Du, Z. Y.; Richard, P.; Yang, H.; Wu, X. X.; Zhang, P.; Qian, T.; Ding, X. X.; Wang, Z. Y. et al. Observation of a Van Hove singularity and implication for strong-coupling induced Cooper pairing in KFe2As2. Phys. Rev. B 2015, 92, 144513.
Crossref Google Scholar
24

Yang, X.; Du, Z. Y.; Lin, H.; Fang, D. L.; Yang, H.; Zhu, X. Y.; Wen, H. H. Vortex lattice and vortex bound states in CsFe2As2 investigated by scanning tunneling microscopy/spectroscopy. Phys. Rev. B 2018, 98, 024505.
Crossref Google Scholar
25

Liu, X.; Tao, R.; Ren, M. Q.; Chen, W.; Yao, Q.; Wolf, T.; Yan, Y. J.; Zhang, T.; Feng, D. L. Evidence of nematic order and nodal superconducting gap along[110] direction in RbFe2As2. Nat. Commun. 2019, 10, 1039.
Crossref Google Scholar
26

Gao, M.; Ma, F. J.; Lu, Z. Y.; Xiang, T. Surface structures of ternary iron arsenides AFe2As2 (A = Ba, Sr, or Ca). Phys. Rev. B 2010, 81, 193409.
Crossref Google Scholar
27

Li, G. R.; Liang, L. B.; Li, Q.; Pan, M. H.; Nascimento, V. B.; He, X. B.; Karki, A. B.; Meunier, V.; Jin, R. Y.; Zhang, J. D. et al. Role of antiferromagnetic ordering in the (1×2) surface reconstruction of Ca(Fe1-xCox)2As2. Phys. Rev. Lett. 2014, 112, 077205.
Crossref Google Scholar
28

Wilfert, S.; Schmitt, M.; Schmidt, H.; Mauerer, T.; Sessi, P.; Wang, H. D.; Mao, Q. H.; Fang, M. H.; Bode, M. Scanning tunneling microscopy and spectroscopy studies of the heavy-electron superconductor TlNi2Se2. Phys. Rev. B 2018, 97, 014514.
Crossref Google Scholar
29

Iyo, A.; Kawashima, K.; Kinjo, T.; Nishio, T.; Ishida, S.; Fujihisa, H.; Gotoh, Y.; Kihou, K.; Eisaki, H.; Yoshida, Y. New-structure-type Fe- based superconductors: CaAFe4As4 (A = K, Rb, Cs) and SrAFe4As4 (A = Rb, Cs). J. Am. Chem. Soc. 2016, 138, 3410-3415.
Crossref Google Scholar
30

Meier, W. R.; Kong, T.; Bud'ko, S. L.; Canfield, P. C. Optimization of the crystal growth of the superconductor CaKFe4As4 from solution in the FeAs-CaFe2As2-KFe2As2 system. Phys. Rev. Mater. 2017, 1, 013401.
Crossref Google Scholar
31

Fente, A.; Meier, W. R.; Kong, T.; Kogan, V. G.; Bud'ko, S. L.; Canfield, P. C.; Guillamón, I.; Suderow, H. Influence of multiband sign-changing superconductivity on vortex cores and vortex pinning in stoichiometric high-Tc CaKFe4As4. Phys. Rev. B 2018, 97, 134501.
Crossref Google Scholar
32

Tersoff, J.; Hamann, D. R. Theory and application for the scanning tunneling microscope. Phys. Rev. Lett. 1983, 50, 1998-2001.
Crossref Google Scholar
33

Vogt, P.; De Padova, P.; Quaresima, C.; Avila, J.; Frantzeskakis, E.; Asensio, M. C.; Resta, A.; Ealet, B.; Le Lay, G. Silicene: Compelling experimental evidence for graphenelike two-dimensional silicon. Phys. Rev. Lett. 2012, 108, 155501.
Crossref Google Scholar
34

Li, L. F.; Lu, S. Z.; Pan, J. B.; Qin, Z. H.; Wang, Y. Q.; Wang, Y. L.; Cao, G. Y.; Du, S. X.; Gao, H. J. Buckled germanene formation on Pt(111). Adv. Mater. 2014, 26, 4820-4824.
Crossref Google Scholar
35

Song, C. L.; Zhang, H. M.; Zhong, Y.; Hu, X. P.; Ji, S. H.; Wang, L. L.; He, K.; Ma, X. C.; Xue, Q. K. Observation of double-dome superconductivity in potassium-doped FeSe thin films. Phys. Rev. Lett. 2016, 116, 157001.
Crossref Google Scholar
36

Ren, M. Q.; Yan, Y. J.; Niu, X. H.; Tao, R.; Hu, D.; Peng, R.; Xie, B. P.; Zhao, J.; Zhang, T.; Feng, D. L. Superconductivity across Lifshitz transition and anomalous insulating state in surface K-dosed (Li0.8Fe0.2OH)FeSe. Sci. Adv. 2017, 3, e1603238.
Crossref Google Scholar
37

Zhu, X. Y.; Wang, S.; Jia, Z. Y.; Zhu, L.; Li, Q. Y.; Zhao, W. M.; Xue, C. L.; Xu, Y. J.; Ma, Z.; Wen, J. S. et al. Realization of a metallic state in 1T-TaS2 with persisting long-range order of a charge density wave. Phys. Rev. Lett. 2019, 123, 206405.
Crossref Google Scholar
38

Mou, D. X.; Kong, T.; Meier, W. R.; Lochner, F.; Wang, L. L.; Lin, Q. S.; Wu, Y.; Bud'ko, S. L.; Eremin, I.; Johnson, D. D. et al. Enhancement of the superconducting gap by nesting in CaKFe4As4: A new high temperature superconductor. Phys. Rev. Lett. 2016, 117, 277001.
Crossref Google Scholar
39

Kresse, G.; Hafner, J. Ab initio molecular dynamics for liquid metals. Phys. Rev. B 1993, 47, 558-561.
Crossref Google Scholar
40

Kresse, G.; Furthmuller, J. Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set. Comp. Mater. Sci. 1996, 6, 15-50.
Crossref Google Scholar
41

Blöchl, P. E. Projector augmented-wave method. Phys. Rev. B 1994, 50, 17953-17979.
Crossref Google Scholar
42

Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized gradient approximation made simple. Phys. Rev. Lett. 1996, 77, 3865-3868.
Crossref Google Scholar
43

Anisimov, V. I.; Zaanen, J.; Andersen, O. K. Band theory and Mott insulators: Hubbard U instead of stoner I. Phys. Rev. B 1991, 44, 943-954.
Crossref Google Scholar
44

Monkhorst, H. J.; Pack, J. D. Special points for Brillouin-zone integrations. Phys. Rev. B 1976, 13, 5188-5192.
Crossref Google Scholar
Nano Research
Volume 14 Issue 11,
November 2021
Pages 3921-3925
DOI: 10.1007/s12274-021-3316-0
Cite this article:
Cao L, Song Y, Liu Y-B, et al. The As-surface of an iron-based superconductor CaKFe4As4. Nano Research, 2021, 14(11): 3921-3925. https://doi.org/10.1007/s12274-021-3316-0
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Received: 15 November 2020
Revised: 16 December 2020
Accepted: 04 January 2021
Published: 24 February 2021
© Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2021
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