The ground state of K${}_{0.8+x}$Fe${}_{1.6+y}$Se${}_2$ and other iron-based selenide superconductors are doped antiferromagnetic semiconductors. We propose that the low energy physics of this system is governed by a model Hamiltonian of interacting electrons with onsite ferromagnetic exchange interactions and intersite superexchange interactions. We have derived the effective pairing potential of electrons under the linear spin-wave approximation and shown that the superconductivity can be driven by mediating coherent spin-wave excitations in these materials. Our work provides a natural account for the coexistence of superconducting and antiferromagnetic long range orders observed by neutron scattering and other experiments.

• Received 6 May 2011

DOI:https://doi.org/10.1103/PhysRevB.84.052502