Article

# Robustness of s-Wave Pairing in Electron-Overdoped A1-yFe2-xSe2 (A=K, Cs)

Physical Review X 09/2011; 1(1). DOI: 10.1103/PhysRevX.1.011009
Source: arXiv

ABSTRACT Using self-consistent mean-field and functional renormalization-group approaches, we show that s-wave pairing symmetry is robust in the heavily electron-doped iron chalcogenides AFe2-xSe2, where A=K, Cs. Recent neutron scattering experiments suggest that the effective nearest-neighbor spin exchange may be ferromagnetic in chalcogenides. This is different from the iron pnictides, where the nearest-neighbor magnetic exchange coupling is believed to be antiferromagnetic and leads to strong competition between s-wave and d-wave pairing in the electron-overdoped region. Our finding of a robust s-wave pairing in (K, Cs)Fe2-xSe2 differs from the d-wave pairing result obtained by other theories where nonlocal bare interaction terms and the next-to-nearest-neighbor J2 term are underestimated. Detecting the pairing symmetry in (K, Cs)Fe2-xSe2 may hence provide important insights regarding the mechanism of superconducting pairing in iron-based superconductors.

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Available from: Ronny Thomale, Aug 06, 2015
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• "However, although the parent compounds of iron pnictide superconductors have metallic ground states consistent with band structure calculations, there are reasons to believe that electron correlations could be sufficiently strong to produce an " incipient " Mott physics [43] [44], where local moments are as important as itinerant electrons for magnetic, transport, and superconducting properties in these materials [45] [46]. In fact, the s ± pairing symmetry is also naturally derived in multi-orbital t − J-type models [47] [48] and recent diagonalization calculations [49] have shown that the AF state, as well as the A 1g s-wave pairing state, evolve smoothly from weak to strong coupling, suggesting that the physics of the pnictides could also be rationalized based on short length scale concepts not rooted in weak-coupling nesting. After all, in the context of the copper oxide superconductors, weak coupling studies of the one-orbital Hubbard model also led to the correct checkerboard AF state and d-wave pairing, showing that these problems can be attacked from a variety of view points. "
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