Evidence of electron interaction with an unidentified bosonic mode in superconductor CsCa2Fe4As4F2 Article Swipe
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· 2024
· Open Access
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· DOI: https://doi.org/10.1038/s41467-024-50833-9
· OA: W4401178856
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<sub>2</sub>Fe<sub>4</sub>As<sub>4</sub>F<sub>2</sub> 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>Γ</mml:mi> <mml:mo>-</mml:mo> <mml:mi>M</mml:mi></mml:math> direction at the band with d<sub>xz</sub> orbital character and vanishes when approaching the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>Γ</mml:mi> <mml:mo>-</mml:mo> <mml:mi>X</mml:mi></mml:math> 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 (~ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mn>9</mml:mn> <mml:mo>±</mml:mo> <mml:mn>1</mml:mn></mml:math> 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.
