The recent discovery of superconductivity at moderately high temperature (26 K to 55 K) in doped iron-based pnictides (LnO_{1-x}F_xFeAs, where Ln = La, Ce, Sm, Pr, Nd, etc.), having layered-structure-like cuprates, has triggered renewed challenge towards understanding the pairing mechanism. After reviewing the current findings on these systems, a theoretical model of a combined mechanism is suggested in which the phonon-mediated and distortion-field-mediated pairing processes give the right order of superconducting critical temperature T_c. The distortion-field modes arise from Jahn-Teller or pseudo Jahn-Teller effects due to degenerate or near-degenerate iron 3d_{xz} and 3d_{yz} orbitals.
Download