Perturbation Theory of High-Tc Superconductivity in Iron Pnictides

Abstract

The high-transition-temperature (high-Tc) superconductivity discovered recently in iron pnictides is analyzed within a perturbation theory. Specifically, the probable pairing symmetry, the doping dependence of the transition temperature and the pairing mechanism are studied by solving the Eliashberg equation for multi-band (2- and 5-band) Hubbard models with realistic electronic structures. The effective pairing interaction is expanded perturbatively in the on-site Coulomb integrals up to third order. Our perturbative weak-coupling approach shows that sufficiently large eigenvalues of the Eliashberg equation are obtained to explain the actual high transition temperatures by taking realistic on-site Coulomb integrals in the 5-band model. Thus, unconventional (non-phonon-mediated) superconductivity is highly likely to be realized. The superconducting order parameter does not change its sign on the Fermi surfaces, but it does change between the electron and hole Fermi surfaces. Consequently, the probable pairing symmetry is always "a nodeless extended s-wave symmetry (more specifically, an s_{+-}-wave symmetry)" over the whole parameter region that we investigated. It is suggested that the 2-band model is insufficient to explain the high values of Tc.

arXiv comment24 pages, 9 figures

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• Microwave Surface-Impedance Measurements of the Magnetic Penetration Depth in Single Crystal Ba1-xKxFe2As2 Superconductors: Evidence for a Disorder-Dependent Superfluid Density
• Possible Multiple Gap Superconductivity with Line Nodes in Heavily Hole-Doped Superconductor KFe2As2 Studied by 75As-NQR and Specific Heat
• First-principles calculation of transition-metal impurities in LaFeAsO
• Possible three dimensional nodes in the $s\pm$ superconducting gap of BaFe${}_2$(As${}_{1-x}$P${}_x$)${}_2$
• Is Fermi-surface nesting the origin of superconductivity in iron pnictides?: A fluctuation-exchange-approximation study
• Impurity-induced in-gap state and Tc in sign-reversing s-wave superconductors: analysis of iron oxypnictide superconductors
• Doping dependence of spin fluctuations and electron correlations in iron pnictides
• Single Impurity Problem in Iron-Pnictide Superconductors
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• Effect of electron-phonon interactions on orbital fluctuations in iron-based superconductors
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• Surface Bound States in n-band Systems with Quasiclassical Approach
• Orbital-Selective Superconductivity and the Effect of Lattice Distortion in Iron-Based Superconductors
• Simple Real-Space Picture of Nodeless and Nodal s-wave Gap Functions in Iron Pnictide Superconductors
• Superconductivity in a Two-Orbital Hubbard Model with Electron and Hole Fermi Pockets: Application in Iron Oxypnictide Superconductors
• Unconventional $s$-Wave Pairing with Point-Node-Like Gap Structure in UTe${}_2$
• Impurity Scattering Rate and Coherence factor in Vortex Core of Sign-reversing s-wave Superconductors
• Weak-Coupling Theory for Multiband Superconductivity Induced by Jahn-Teller Phonons
• Coherence effect in a two-band superconductor: Application to iron pnictides