Pairing Symmetry and Spin Excitations of Iron Selenide Superconductors

TL;DR

This paper introduces a minimal single-band model for iron selenide superconductors, revealing d-wave pairing symmetry and explaining spin excitations consistent with experimental observations, thus advancing understanding of high-Tc superconductivity.

Contribution

It proposes a new effective model and demonstrates d-wave pairing symmetry in iron selenide superconductors, linking Fermi surface topology to pairing mechanisms.

Findings

D-wave pairing symmetry is theoretically confirmed.

Spin excitations at specific wave vectors match experimental data.

Spin resonance appears only with d-wave pairing.

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.