Near-degeneracy of several pairing channels in multiorbital models for the Fe pnictides

By T. Maier, S. Graser, P. Hirschfeld, Douglas J. Scalapino. 2008

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Weak-coupling approaches to the pairing problem in the iron pnictide superconductors have predicted a wide variety of superconducting ground states. We argue here that this is due both to the inadequacy of certain approximations to the effective low-energy band structure, and to the natural near degeneracy of different pairing channels in superconductors with many distinct Fermi surface sheets. In particular, we review attempts to construct two-orbital effective band models, the argument for their fundamental inconsistency with the symmetry of these materials, and compare the dynamical susceptibilities of two- and five-orbital tight-binding models. We then present results for the magnetic properties, pairing interactions and pairing instabilities within a five-orbital tight-binding random phase approximation model. We discuss the robustness of these results for different dopings, interaction strengths and variations in band structures. Within the parameter space explored, an anisotropic, sign-changing s-wave (A1g) state and a (B1g) state are nearly degenerate, due to the near nesting of Fermi surface sheets.

Subfields: Atomic and Molecular Physics, and Optics, Condensed Matter Physics, Electronic, Optical and Magnetic Materials

View Paper: https://www.semanticscholar.org/paper/56c9ba99528abda22fcf44f3c0f61b010cd98d1f

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In Atomic and Molecular Physics, and Optics

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Citations in the corpus

Symmetry-breaking orbital anisotropy observed for detwinned Ba(Fe1-xCox)2As2 above the spin density wave transition (2010, background): “tional symmetry is spontaneously broken without breaking translational symmetry (1-2). Two well established examples are found in certain quantum Hall states (3) and in the bilayer ruthenate Sr3Ru2O7 (4), both of which exhibit a large transport anisotropy under the application of large magnetic fiel”
Iron-based superconductors at high magnetic fields (2011, background): “This situation is rather common in FBSs in which several bands with large effective masses are often situated just slightly below the Fermi level at or close to the optimal doping as has been revealed by ab initio calculations [48–50], dHvA oscillations [55–58] and ARPES [51–54] (see figure 9).”
Functional renormalization group approach to correlated fermion systems (2011, background): “(115) The combination of ubos behind the interaction tensor is sometimes called the ’orbital make-up’ (Graser et al., 2009; Maier et al., 2009).”
High-temperature superconductivity in iron-based materials (2010, background): “Moreover, owing to the multi-orbital nature of the FeSCs and their nesting properties, anisotropic (extended) s - and d -wave states are nearly degenerat”
Normal-state spin dynamics and temperature-dependent spin-resonance energy in optimally doped BaFe 1.85 Co 0.15 As 2 (2009, background): “that electron–phonon coupling is too weak to explain the high T c , which turns the spotlight onto the magnetic coupling channel agai”