41 research outputs found
A weak-coupling superconductivity in the electron doped NaFeCoAs is revealed by ARPES
We report a systematic study on the electronic structure and superconducting
(SC) gaps in electron doped NaFeCoAs superconductor using
angle-resolved photoemission spectroscopy. Hole-like Fermi sheets are at the
zone center and electron-like Fermi sheets are at the zone corner, and are
mainly contributed by and orbital characters. Our results reveal a
in the range of 1.8-2.1, suggesting a weak-coupling
superconductivity in these compounds. Gap closing above the transition
temperature () shows the absence of pseudogaps. Gap evolution with
temperature follow the BCS gap equation near the , , and high
symmetry points. Furthermore, an almost isotropic superconductivity along
direction in the momentum space is observed by varying the excitation energies.Comment: 6 pages, 5 figures, Accepted by Phy.Rev.
Weak-coupling superconductivity in a strongly correlated iron pnictide
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
NaFeCoAs 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 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.Comment: Open access article available online at
http://www.nature.com/articles/srep1862
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Weak-coupling superconductivity in a strongly correlated iron pnictide
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
Non-Fermi-liquid scattering rates and anomalous band dispersion in ferropnictides
Angle-resolved photoemission spectroscopy (ARPES) is used to study the band
dispersion and the quasiparticle scattering rates in two ferropnictides
systems. Our ARPES results show linear-in-energy dependent scattering rates
which are constant in a wide range of control parameter and which depend on the
orbital character of the bands. We demonstrate that the linear energy
dependence gives rise to weakly dispersing band with a strong mass enhancement
when the band maximum crosses the chemical potential. In the superconducting
phase the related small effective Fermi energy favors a
Bardeen-Cooper-Schrieffer (BCS)\,\cite{Bardeen1957}-Bose-Einstein
(BE)\,\cite{Bose1924} crossover state.Comment: 5 pages, 4 figures Supplement 4 pages, 6 figure