Abstract
We analyze the magnetic excitations and the spin-mediated superconductivity in iron-based superconductors within a low energy model that operates in the band basis, but fully incorporates the orbital character of the spin excitations. We show how the orbital selectivity, encoded in our low energy description, simplifies substantially the analysis and allows for analytical treatments, while retaining all the main features of both spin excitations and gap functions computed using multiorbital models. Importantly, our analysis unveils the orbital matching between the hole and electron pockets as the key parameter to determine the momentum dependence and the hierarchy of the superconducting gaps, instead of the Fermi surface matching, as in the common nesting scenario.
Highlights
Instituto de Ciencia de Materiales de Madrid, ICMM-CSIC, Cantoblanco, Department of Physics, University of Florida, Gainesville, FL 32611, USA
It has been shown that for iron-based superconductors (IBSs), the charge susceptibility is more than one order of magnitude smaller than the spin susceptibility; hereafter, we focus on the spin channel only
We showed that the orbital selective spin fluctuation (OSSF) model provides a reliable description of the magnetic excitations in IBSs and represents the minimal model to study spin-mediated superconductivity in this system
Summary
The discovery of iron-based superconductors (IBSs) raised immediate questions about the nature of the superconducting (SC) state and the pairing mechanism. Given the repulsive and interband character of the interaction, the expected symmetry for the gap function is the so-called s± , i.e., an isotropic s-wave on each pocket with opposite signs for hole and electron pockets This picture has been supported and confirmed by extensive theoretical works that, within realistic multiorbital interacting models for IBSs, provide a quantitative estimate of the SC properties starting from a random phase approximation (RPA)-based description of the spin-susceptibility [5,6,7,8,9,10,11]. Our analysis demonstrates that the degree of orbital nesting is the parameter that controls the modulation and the hierarchy of the SC gaps This last observation counters the naive expectation of stronger pairing between matching Fermi surfaces and forces us to revise the band nesting paradigm in the light of the orbital degree of freedom
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