Evidence of electron interaction with an unidentified bosonic mode in superconductor CsCa2Fe4As4F2

Peng Li; Sen Liao; Zhicheng Wang; Huaxun Li; Shiwu Su; Jiakang Zhang; Ziyuan Chen; Zhicheng Jiang; Zhengtai Liu; Lexian Yang; Linwei Huai; Junfeng He; Shengtao Cui; Zhe Sun; Yajun Yan; Guanghan Cao; Dawei Shen; Juan Jiang; Donglai Feng

doi:10.1038/s41467-024-50833-9

Evidence of electron interaction with an unidentified bosonic mode in superconductor CsCa₂Fe₄As₄F₂

Nat Commun. 2024 Jul 31;15(1):6433. doi: 10.1038/s41467-024-50833-9.

Authors

Peng Li¹, Sen Liao¹, Zhicheng Wang², Huaxun Li³, Shiwu Su¹, Jiakang Zhang¹, Ziyuan Chen¹, Zhicheng Jiang^{4

5}, Zhengtai Liu⁶, Lexian Yang⁷, Linwei Huai⁸, Junfeng He⁸, Shengtao Cui⁴, Zhe Sun⁴, Yajun Yan¹, Guanghan Cao³, Dawei Shen^{4

5}, Juan Jiang⁹, Donglai Feng^{10

11

12

13}

Affiliations

¹ Shool of Emerging Technology, University of Science and Technology of China, Hefei, 230026, China.
² Key Laboratory of Quantum Materials and Devices of Ministry of Education, School of Physics, Southeast University, Nanjing, 211189, China.
³ School of Physics, Zhejiang University, Hangzhou, 310058, China.
⁴ National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, 230026, China.
⁵ School of Nuclear Science and Technology, University of Science and Technology of China, Hefei, 230026, China.
⁶ Shanghai Synchrotron Radiation Facility, Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai, 201210, China.
⁷ State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing, 100084, China.
⁸ CAS Key Laboratory of Strongly-coupled Quantum Matter Physics, University of Science and Technology of China, Hefei, Anhui, 230026, China.
⁹ Shool of Emerging Technology, University of Science and Technology of China, Hefei, 230026, China. [email protected].
¹⁰ Shool of Emerging Technology, University of Science and Technology of China, Hefei, 230026, China. [email protected].
¹¹ National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, 230026, China. [email protected].
¹² School of Nuclear Science and Technology, University of Science and Technology of China, Hefei, 230026, China. [email protected].
¹³ New Cornerstone Science Laboratory, University of Science and Technology of China, Hefei, 230026, China. [email protected].

Abstract

The kink structure in band dispersion usually refers to a certain electron-boson interaction, which is crucial in understanding the pairing in unconventional superconductors. Here we report the evidence of the observation of a kink structure in Fe-based superconductor CsCa₂Fe₄As₄F₂ using angle-resolved photoemission spectroscopy. The kink shows an orbital selective and momentum dependent behavior, which is located at 15 meV below Fermi level along the $Γ - M$ direction at the band with d_xz orbital character and vanishes when approaching the $Γ - X$ direction, correlated with a slight decrease of the superconducting gap. Most importantly, this kink structure disappears when the superconducting gap closes, indicating that the corresponding bosonic mode (~ $9 \pm 1$ meV) is closely related to superconductivity. However, the origin of this mode remains unidentified, since it cannot be related to phonons or the spin resonance mode (~15 meV) observed by inelastic neutron scattering. The behavior of this mode is rather unique and challenges our present understanding of the superconducting paring mechanism of the bilayer FeAs-based superconductors.

Grants and funding

12174362/National Natural Science Foundation of China (National Science Foundation of China)