Crossover from weak to strong pairing in unconventional superconductors

Abstract

Superconductors are classified by their pairing mechanism and the coupling strength, measured as the ratio of the energy gap to the critical temperature, Tc. We present an extensive comparison of the gap ratios among many single- and multiband superconductors from simple metals to high-Tc cuprates and iron pnictides. Contrary to the recently suggested universality of this ratio in Fe-based superconductors, we find that the coupling in pnictides ranges from weak, near the BCS limit, to strong, as in cuprates, bridging the gap between these two extremes. Moreover, for Fe- and Cu-based materials, our analysis reveals a universal correlation between the gap ratio and Tc, which is not found in conventional superconductors and therefore supports a common unconventional pairing mechanism in both families. An important consequence of this result for ferropnictides is that the separation in energy between the excitonic spin-resonance mode and the particle-hole continuum, which determines the resonance damping, no longer appears independent of Tc.

15 pages, 3 figures, 5 tables with an exhaustive overview of the published gap and spin-resonance measurements in Fe-based superconductors. New in V3: updated references. To be published in Phys. Rev. B

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Cited by in corpus (17)

• Magnetism and its microscopic origin in iron-based high-temperature superconductors
• Electron doping evolution of the anisotropic spin excitations in BaFe2-xNixAs2
• Interaction-induced singular Fermi surface in a high-temperature oxypnictide superconductor
• Hydrostatic-pressure effects on the pseudogap in slightly doped YBa2Cu3O7-δ single crystals
• Optical conductivity of iron-based superconductors
• Robust Upward Dispersion of the Neutron Spin Resonance in the Heavy Fermion Superconductor Ce${}_{1-x}$Yb${}_x$CoIn${}_5$
• Comprehensive Eliashberg analysis of microwave conductivity and penetration depth of K-, Co-, and P-substituted BaFe2As2
• Electronic band structure and momentum dependence of the superconducting gap in (Ca, Na)Fe2As2 from angle-resolved photoemission spectroscopy
• Anisotropic neutron spin resonance in underdoped superconducting NaFe1-xCoxAs
• Polarized neutron scattering studies of magnetic excitations in electron-overdoped superconducting BaFe${}_{1.85}$Ni${}_{0.15}$As${}_2$
• Magnonlike dispersion of spin resonance in Ni-doped BaFe${}_2$As${}_2$
• Superconducting properties and pseudogap from preformed Cooper pairs in the triclinic (CaFe${}_{1-x}$Pt${}_x$As)${}_{10}$Pt${}_3$As${}_8$
• Effects of isoelectronic Ru substitution at the Fe site on the energy gaps of optimally F-doped SmFeAsO
• Phase diagram and neutron spin resonance of superconducting NaFe${}_{1-x}$Cu${}_x$As
• Orbital selective neutron spin resonance in underdoped superconducting NaFe${}_{\text{0.985}}$Co${}_{\text{0.015}}$As
• Temperature and polarization dependence of low-energy magnetic fluctuations in nearly-optimal-doped NaFe${}_{0.9785}$Co${}_{0.0215}$As
• Doping evolution of the gap structure and spin-fluctuation pairing in $Ba(F{e}_{1-x}C{o}_x{)}_{2}A{s}_2$ superconductors