Pairing Symmetry and Spin Excitations of Iron Selenide Superconductors

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.

7 pages, 7 figures. arXiv admin note: significant text overlap with arXiv:1108.3491

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