Band-selective clean- and dirty-limit superconductivity with nodeless gaps in the bilayer iron-based superconductor CsCa${}_2$Fe${}_4$As${}_4$F${}_2$

Abstract

The optical properties of the new iron-based superconductor CsCa${}_2$Fe${}_4$As${}_4$F${}_2$ with $T_c\sim 29$~K have been determined. In the normal state a good description of the low-frequency response is obtained with a superposition of two Drude components of which one has a very low scattering rate (narrow Drude-peak) and the other a rather large one (broad Drude-peak). Well below $T_c\sim 29$~K, a pronounced gap feature is observed which involves a complete suppression of the optical conductivity below $\sim$ 110~cm${}^{-1}$ and thus is characteristic of a nodeless superconducting state. The optical response of the broad Drude-component can be described with a dirty-limit Mattis-Bardeen-type response with a single isotropic gap of $2\Delta \simeq 14$~meV. To the contrary, the response of the narrow Drude-component is in the ultra-clean-limit and its entire spectral weight is transferred to the zero-frequency $\delta (\omega )$ function that accounts for the loss-free response of the condensate. These observations provide clear evidence for a band-selective coexistence of clean- and dirty-limit superconductivity with nodeless gaps in CsCa${}_2$Fe${}_4$As${}_4$F${}_2$.

5 pages, 4 figures

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Cited by in corpus (11)

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• Ultrafast Optical Spectroscopy Evidence of Pseudogap and Electron-Phonon Coupling in an Iron-Based Superconductor KCa${}_2$Fe${}_4$As${}_4$F${}_2$
• NMR and NQR studies on transition-metal arsenide superconductors LaRu2As2, KCa2Fe4As4F2, and A2Cr3As3
• Nodal multigap superconductivity in the anisotropic iron-based compound RbCa2Fe4As4F2
• Pseudogap and Strong Pairing Induced by Incipient and Shallow Bands in the Quasi-Two-Dimensional KCa${}_2$Fe${}_4$As${}_4$F${}_2$
• Spectroscopic studies of the superconducting gap in the 12442 family of iron-based compounds
• Evidence of electron interaction with an unidentified bosonic mode in superconductor CsCa${}_2$Fe${}_4$As${}_4$F${}_2$
• Superconductivity-induced transverse plasma mode and phonon anomaly in the $c$-axis response of the bilayer compound RbCa${}_2$Fe${}_4$As${}_4$F${}_2$
• Interplay of electron-phonon coupling, pseudogap, and superconductivity in CsCa${}_2$Fe${}_4$As${}_4$F${}_2$ studied using ultrafast optical spectroscopy
• Multiband superconductivity and a deep gap minimum from the specific heat in KCa${}_2$(Fe${}_{1-x}$Ni${}_x$)${}_4$As${}_4$F${}_2$ ($x$ = 0, 0.05, 0.13)
• Decoupled interband pairing in a bilayer iron-based superconductor evidenced by ultrahigh-resolution ARPES