| الملخص: | The possibility for an appreciable many-body contribution to the electron-phonon interaction (EPI) in Fe-pnictides is discussed in the model where EPI is due to the electronic polarization of As-ions. The polarization induced EPI pol potential V ep is large for vibrations of the As-ions and depends strongly on the As-Fe distance d, i.e.V ep∼d -4. The EPI pol coupling g eppol is much larger than the one obtained in the LDA band structure calculations, with g eppol (∼16 eV/)≫g ep(LDA) (< 1 eV/) and the bare pairing EPI pol coupling constant λep, A 1g0∼1. It contributes significantly to the intra-band s-wave pairing and an appreciable positive As-isotope effect in the superconducting critical temperature is expected. In the Fe-breathing mode the linear (in the Fe-displacements) EPI pol coupling vanishes, while the non-linear (quadratic) one is very strong. The part of the EPI pol coupling, which is due to the "potential" energy (the Hubbard U) changes, is responsible for the giant magneto-elastic effects in MF e 2As 2, M=Ca, Sr, Ba since it gives much larger contribution to the magnetic pressure than the band structure effects do. This mechanism is contrary to the LDA prediction where the magneto-elastic effects are due to the "kinetic" energy effects, i.e. the changes in the density of states by the magneto-elastic effects. The proposed EPI pol is expected to be operative (and strong) in other Fe-based superconductors with electronically polarizable ions such as Se, Te, S etc., and in high-temperature superconductors due to the polarizability of the O 2--ions. Copyright © 2009 EPLA.
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