d-wave pairing from spin fluctuations in the KxFe{2-y}Se2 superconductors

TL;DR

This paper investigates the pairing mechanism in KxFe{2-y}Se2 superconductors, proposing a d-wave pairing symmetry driven by spin fluctuations, supported by theoretical calculations and suggesting experimental validation methods.

Contribution

It introduces a theoretical model showing d-wave pairing in KxFe{2-y}Se2 due to spin fluctuations, differing from other iron-based superconductors.

Findings

D-wave pairing symmetry is most likely in KxFe{2-y}Se2.

Pair scattering occurs mainly between electron Fermi pockets.

Experimental tests like neutron scattering can validate the model.

Abstract

Angle-resolved photoemission spectroscopy measurements on the recently discovered superconduc- tors in the KFe2Se2 family with critical temperatures up to - 33K suggest that no Fermi pockets of hole character centered on the {\Gamma} point of the Brillouin zone are present, in contrast to all other known ferropnictide and ferrochalcogenide superconductors. Using a fluctuation exchange approximation and a 5-orbital tight-binding description of the band structure, we calculate the effective pairing interaction. We find that the pairing state in this system is most likely to have d-wave symmetry due to pair scattering between the remaining electron Fermi pockets at wave vector q - ({\pi}, {\pi}), but without any symmetry-imposed nodes for the given Fermi surface. We propose experimental tests of this result, including the form of the resonance spectrum probed by inelastic neutron scattering.