Intrinsic Superconducting Gap in Bilayer KCa<sub>2</sub>Fe<sub>4</sub>As<sub>4</sub>F<sub>2</sub> and Decoupled Monolayer FeAs.
basic_science · Level V
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- Record sourced from PubMed, PMID 42396750.
- Also identified by DOI 10.1021/acs.nanolett.6c01952.
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Abstract
Despite extensive progress in iron-based superconductors, how interlayer coupling affects superconductivity remains a key unresolved issue. Here, using angle-resolved photoemission spectroscopy, we successfully resolve the electronic structure of a surface-decoupled FeAs monolayer in KCa<sub>2</sub>Fe<sub>4</sub>As<sub>4</sub>F<sub>2</sub>, a rare example in iron pnictides. This allows for a direct, side-by-side comparison between the basic FeAs unit and its bulk bilayer counterpart within a single sample. Two distinct superconducting phases are identified: a bulk bilayer phase with Tc ∼ 34 K and a surface-decoupled monolayer phase with a smaller gap vanishing at ∼18 K. In addition to probable enhanced fluctuations in single-layer FeAs, we propose that this Tc difference may originate from either interfacial effect, such as phonon-mediated assistance from the CaF layers or electronic interlayer hopping within the bilayer unit. Our work offers a refined framework for understanding the superconductivity in multilayer iron-based superconductors.