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

Physical Review X (Impact Factor: 9.04). 09/2011; 1(1). DOI: 10.1103/PhysRevX.1.011009
Source: arXiv


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.

Download full-text


Available from: Ronny Thomale
  • Source
    • "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. "
    [Show abstract] [Hide abstract]
    ABSTRACT: High-temperature superconductivity in the iron-based materials emerges from, or sometimes coexists with, their metallic or insulating parent compound states. This is surprising since these undoped states display dramatically different antiferromagnetic (AF) spin arrangements and N$\rm \acute{e}$el temperatures. Although there is general consensus that magnetic interactions are important for superconductivity, much is still unknown concerning the microscopic origin of the magnetic states. In this review, progress in this area is summarized, focusing on recent experimental and theoretical results and discussing their microscopic implications. It is concluded that the parent compounds are in a state that is more complex than implied by a simple Fermi surface nesting scenario, and a dual description including both itinerant and localized degrees of freedom is needed to properly describe these fascinating materials.
    Full-text · Article · Sep 2012 · Nature Physics
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Kamihara and coworkers' report of superconductivity at Tc = 26 K in fluorine-doped LaFeAsO inspired a worldwide effort to understand the nature of the superconductivity in this new class of compounds. These iron pnictide and chalcogenide (FePn/Ch) superconductors have Fe electrons at the Fermi surface, plus an unusual Fermiology that can change rapidly with doping, which lead to normal and superconducting state properties very different from those in standard electron-phonon coupled 'conventional' superconductors. Clearly superconductivity and magnetism/magnetic fluctuations are intimately related in the FePn/Ch - and even coexist in some. Open questions, including the superconducting nodal structure in a number of compounds, abound and are often dependent on improved sample quality for their solution. With Tc values up to 56 K, the six distinct Fe-containing superconducting structures exhibit complex but often comparable behaviors. The search for correlations and explanations in this fascinating field of research would benefit from an organization of the large, seemingly disparate data set. This review attempts to provide an overview, using numerous references, with a focus on the materials and their superconductivity.
    Preview · Article · Jun 2011 · Review of Modern Physics
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The multipocket Fermi surfaces of iron-based superconductors promote pairing states with both s_{+-}-wave and d_{x^2-y^2}-wave symmetry. We argue that the competition between these two order parameters could lead to a time-reversal-symmetry breaking state with s+id-pairing symmetry in the iron-based superconductors, and propose serveral scenarios in which this phase may be found. To understand the emergence of such a pairing state on a more rigorous footing, we start from a microscopic 5-orbital description representative for the pnictides. Using a combined approach of functional renormalization group and mean-field analysis, we identify the microscopic parameters of the s+id-pairing state. There, we find the most promising region for s+id-pairing in the electron doped regime with an enhanced pnictogen height.
    Full-text · Article · Jun 2011 · Physical review. B, Condensed matter
Show more