A Possible Pairing Mechanism in Fe-Based High Temperature Superconductors

The electronic structures of LaOFeAs superconductors with antiferromagnetic model were simulated by using the first-principle method. The calculated density of states (DOS) reveals that some antiferromagnetic energy peaks are splitted due to the hybridization of Fe-3d and As-4p on the FeAs layer. The calculated spin moment for LaOFeAs is 2.39 μB/Fe. The band structure and DOS around the Fermi level suggest this compound with a semimetal-like characteristic. Beside on the Fe, a spin polarization occurs on the As site, which is distributed with both As-4p and As-4s orbitals. A unique electronic structure is found to be associated with the deep inner orbital coupling in the LaOFeAs compound, which provides an independent energy band with a high vibration frequency. The two bands with deep inner orbital coupling as well as the spin polarization of As-4s could be used to explain some behaviours of carrier pairing in the superconducting state. In addition, the simulation also was performed on a series of F-doped LaOFeAs with different fluorine composition. The results show with F-doping increasing the spin polarization of As decreasing. Superconductivity will be suppressed by the heavy F-doping concentration.