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

• Published in: Nature communications 2024-07, Vol.15 (1), p.6433-7, Article 6433
• Main Authors: Li, Peng, Liao, Sen, Wang, Zhicheng, Li, Huaxun, Su, Shiwu, Zhang, Jiakang, Chen, Ziyuan, Jiang, Zhicheng, Liu, Zhengtai, Yang, Lexian, Huai, Linwei, He, Junfeng, Cui, Shengtao, Sun, Zhe, Yan, Yajun, Cao, Guanghan, Shen, Dawei, Jiang, Juan, Feng, Donglai
• Format: Article
• Language: English
• Subjects: 140/146; 639/766/119/1003; 639/766/119/995; Humanities and Social Sciences; Inelastic scattering; Momentum; multidisciplinary; Neutron scattering; Photoelectric emission; Resonance scattering; Science; Science (multidisciplinary); Spectroscopy; Spin resonance; Superconductivity; Unconventional superconductors
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-024-50833-9

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 CsCa 2 Fe 4 As 4 F 2 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 ± 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. The kink structure in the band dispersion can be linked to electron-boson interaction and has been reported in unconventional superconductors. Here the authors observe an orbital selective and momentum dependent kink feature in an Fe-based superconductor, which is highly correlated with superconductivity.