Orbital Fluctuation Theory in Iron Pnictides: Effects of As-Fe-As Bond Angle, Isotope Substitution, and $Z^2$-Orbital Pocket on the Superconductivity

Abstract

We study the pairing mechanism in iron pnictide superconductors based on the five-orbital Hubbard-Holstein model. Due to Fe-ion oscillations, the s-wave superconducting (SC) state without sign reversal (s_{++}-wave state) is induced by orbital fluctuations by using realistic model parameters. The virtue of the present theory is that the famous empirical relation between Tc and the As-Fe-As bond angle is automatically explained, since the electron-phonon (e-ph) coupling that creates the orbital fluctuations is the strongest when the As${}_4$-tetrahedron is regular. The negative iron isotope effect is also reproduced. In addition, the magnitude of the SC gap on hole-pockets is predicted to be rather insensitive to the corresponding d-orbital (xz/yz- or z^2-orbital), which is consistent with the recent bulk-sensitive angle-resolved photoemission spectroscopy (ARPES) measurement for (Ba,K)Fe${}_2$As${}_2$ and BaFe${}_2$(As,P)${}_2$. These obtained results indicate that the orbital-fluctuation-mediated s_{++}-wave state is a plausible candidate for iron pnictides.

11 pages, 10 figures, New discussions and figures had been added

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Cited by in corpus (17)

• Self-Consistent Vertex Correction Analysis for Iron-Based Superconductors: Mechanism of Coulomb-Interaction-Driven Orbital Fluctuations
• d-wave pairing from spin fluctuations in the KxFe{2-y}Se2 superconductors
• Phase Diagram of Ba1-xKxFe2As2
• Strong nodeless pairing on separate electron Fermi surface sheets in (Tl, K)Fe${}_{1.78}$Se${}_2$ probed by ARPES
• Emergence of Fully-Gapped $s_{++}$-wave and Nodal d-wave States Mediated by Orbital- and Spin-Fluctuations in Ten-Orbital Model for KFe${}_2$Se${}_2$
• Extraordinary quasiparticle scattering and bandwidth-control by dopants in iron-based superconductors
• Abrupt change in the energy gap of superconducting Ba1-xKxFe2As2 single crystals with hole doping
• Superconducting pairing mediated by spin-fluctuations from first principles
• Non-Fermi-Liquid Transport Phenomena and Superconductivity Driven by Orbital Fluctuations in Iron Pnictides: Analysis by Fluctuation-Exchange Approximation
• A weak-coupling superconductivity in the electron doped NaFe${}_{0.95}$Co${}_{0.05}$As is revealed by ARPES
• Determination of the pairing state in iron-based superconductors through neutron scattering
• Orbital Symmetry and Orbital Excitations in High-$T_c$ Superconductors
• Unconventional Superconductivity arising from Multipolar Kondo Interactions
• Preliminary Tc calculations for iron-based superconductivity in NaFeAs, LiFeAs, FeSe and nanostructured FeSe/SrTiO3 Superconductors
• Effect of inelastic scattering on the nuclear magnetic relaxation rate 1/T1T in iron-based superconductors
• Comment on "Orbital Order, Structural Transition and Superconductivity in Iron Pnictides" [arXiv:1010.0129] by Yanagi et al
• Fe-vacancy ordered Fe4Se5: The insulating parent phase of FeSe superconductor