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 NaFe${}_{0.978}$Co${}_{0.022}$As 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 $\Gamma$ 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.

arXiv commentOpen access article available online at http://www.nature.com/articles/srep18620

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• The three-dimensional electronic structure of the nematic and antiferromagnetic phases of NaFeAs from detwinned ARPES measurements
• Hund's metal crossover and superconductivity in the 111 family of iron-based superconductors
• Dynamical susceptibility of a near-critical non-conserved order parameter and B2g Raman response in Fe-based superconductors
• Intrinsic charge dynamics in high-Tc AFeAs(O,F) superconductors
• Temperature and polarization dependence of low-energy magnetic fluctuations in nearly-optimal-doped NaFe${}_{0.9785}$Co${}_{0.0215}$As
• Effect of electron doping in FeTe${}_{1-y}$Se${}_y$ realized by Co and Ni substitution
• Infrared spectroscopy study of the in-plane response of YBa2Cu3O6.6 in magnetic fields up to 30 Tesla