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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Article: Pairing Symmetry and Spin Excitations of Iron Selenide Superconductors
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ABSTRACT: We propose an effective single-band model for the newly discovered iron selenide superconductors A$_x$Fe$_{2-y}$Se$_2$ (A=Tl,K,Rb,Cs). Based on this minimum model and the random phase approximation, the $d_{x^2-y^2}$ pairing symmetry is revealed theoretically, which may be understood in the framework of Fermi surface topology. A common origin of superconductivity is elucidated for this compound and other high-T$_c$ materials. The spin excitations at $(\pi,\pi/2)$ in superconducting states are observed, in good agreement with the neutron scattering experiments. The spin resonance is indicated to show up only for the d-wave pairing, which provides an additional indication for the d-wave pairing symmetry in this family of superconductors.
02/2012;