Perturbation theory of iron-pnictide superconductivity

Nomura, Takuji

The high- superconductivity in iron pnictides is studied within a perturbation theory. We employ a five-band Hubbard model taking account of five Fe3-like local orbitals. The Eliashberg equation is solved by calculating the pairing interaction within the third-order perturbation expansion in the Coulomb interaction at iron sites. The superconducting order parameter changes sign between the disconnected Fermi surfaces, and the superconducting gap is fully opened without any nodes on the Fermi surface. The most favorable pairing symmetry is an -wave. It is suggested that the superconductivity disappears in high doping regions where the electron pockets or the hole pockets disappear.