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Deutsche Physikalische Gessellschaft IOP Institute of Physics

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

Focus on Iron-Based Superconductors

S Graser1,4, T A Maier2, P J Hirschfeld1 and D J Scalapino3

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Part of Focus on Iron-Based Superconductors

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 {\rm d}_{{x}{}^{2}\scriptsize{-}{y}{}^{2}} (B1g) state are nearly degenerate, due to the near nesting of Fermi surface sheets.


PACS

74.25.Jb Electronic structure

74.25.Ha Magnetic properties

74.70.Dd Ternary, quaternary and multinary compounds (including Chevrel phases, borocarbides, etc.)

71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Subjects

Superconductivity

Condensed matter: electrical, magnetic and optical

Dates

Issue 2 (February 2009)

Received 28 November 2008

Published 27 February 2009



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