title: Weak-coupling superconductivity in a strongly correlated iron pnictide.
abstract: Iron-based superconductors have been found to exhibit an intimate interplay of orbital, spin, and lattice degrees of freedom, dramatically affecting their low-energy electronic properties, including superconductivity. Albeit the precise pairing mechanism remains unidentified, several candidate interactions have been suggested to mediate the superconducting pairing, both in the orbital and in the spin channel. Here, we employ optical spectroscopy (OS), angle-resolved photoemission spectroscopy (ARPES), ab initio band-structure, and Eliashberg calculations to show that nearly optimally doped NaFe0.978Co0.022As exhibits some of the strongest orbitally selective electronic correlations in the family of iron pnictides. Unexpectedly, we find that the mass enhancement of itinerant charge carriers in the strongly correlated band is dramatically reduced near the Γ point and attribute this effect to orbital mixing induced by pronounced spin-orbit coupling. Embracing the true band structure allows us to describe all low-energy electronic properties obtained in our experiments with remarkable consistency and demonstrate that superconductivity in this material is rather weak and mediated by spin fluctuations.
authors.affiliation: Physics Department, University of California-San Diego, La Jolla, CA 92093, USA.|Leibniz Institute for Solid State and Materials Research, IFW, 01069 Dresden, Germany.|Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Charnukha
authors.affiliation: Physics Department, University of California-San Diego, La Jolla, CA 92093, USA.
authors.forename: K W
authors.initials: KW
authors.lastname: Post
authors.affiliation: Leibniz Institute for Solid State and Materials Research, IFW, 01069 Dresden, Germany.|Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore-560 012, India.
authors.forename: S
authors.initials: S
authors.lastname: Thirupathaiah
authors.affiliation: Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany.
authors.forename: D
authors.initials: D
authors.lastname: Pröpper
authors.affiliation: Leibniz Institute for Solid State and Materials Research, IFW, 01069 Dresden, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Wurmehl
authors.affiliation: Leibniz Institute for Solid State and Materials Research, IFW, 01069 Dresden, Germany.|Department of Chemistry, Moscow State University, 119991 Moscow, Russia.
authors.forename: M
authors.initials: M
authors.lastname: Roslova
authors.affiliation: Leibniz Institute for Solid State and Materials Research, IFW, 01069 Dresden, Germany.|Department of Chemistry, Moscow State University, 119991 Moscow, Russia.
authors.forename: I
authors.initials: I
authors.lastname: Morozov
authors.affiliation: Leibniz Institute for Solid State and Materials Research, IFW, 01069 Dresden, Germany.
authors.forename: B
authors.initials: B
authors.lastname: Büchner
authors.affiliation: Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany.
authors.forename: A N
authors.initials: AN
authors.lastname: Yaresko
authors.affiliation: Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany.
authors.forename: A V
authors.initials: AV
authors.lastname: Boris
authors.affiliation: Leibniz Institute for Solid State and Materials Research, IFW, 01069 Dresden, Germany.
authors.forename: S V
authors.initials: SV
authors.lastname: Borisenko
authors.affiliation: Physics Department, University of California-San Diego, La Jolla, CA 92093, USA.
authors.forename: D N
authors.initials: DN
authors.lastname: Basov