Stripes, spin resonance, and nodeless d-wave pairing symmetry in Fe2Se2-based layered superconductors

Abstract

We calculate RPA-BCS-based spin resonance spectra of the newly discovered iron-selenide superconductor by using the two-orbital tight-binding model in a 1-Fe-unit cell. The slightly squarish electron pocket Fermi surfaces at (π,0)/(0,π) momenta produce leading interpocket nesting instability at incommensurate vector q∼(π,0.5π) in the normal-state static susceptibility, pinning a strong stripe-like spin-density wave or antiferromagnetic order at some critical value of U. The same nesting also induces dx2−y2 pairing in a 1-Fe-unit cell. The superconducting gap is nodeless and isotropic on the Fermi surfaces, as they lie concentric to the fourfold symmetric point of the d-wave gap maxima, in agreement with various experiments. This produces a slightly incommensurate spin resonance with upward dispersion, in close agreement with neutron data on chalcogenides. Finally, we demonstrate the conversion procedure from a 1-Fe-unit cell to a 2-Fe-unit cell in which the gap symmetry transformed simultaneously into a dxy pairing and the resulting resonance spectrum moves from the q≃(π,π) to the q≃(2π,0)/(2π,0) region.

Source-reported materials — not catalogue approval

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