, Volume 22, Issue 6, pp 603-607
Date: 22 Apr 2009

Iron-Based Layered Compounds: The Effect of Negative Interband Coupling

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The experimental data relative to new superconductor LaFeAsO1−x F x can be analyzed in the framework of the two-band Eliashberg theory. With reasonable assumptions on input parameters of the theory such as electron–phonons and electron-antiferromagnetic spin density fluctuations spectral functions and the Coulomb pseudopotential, it is possible to calculate mean physical quantities such as critical temperature, superconductive gaps, superconductive differential conductance, and so on. In this model also the effect of disorder and magnetic impurities on the critical temperature is examined. The key ingredient is the negative interband coupling that can remarkably increase the critical temperature. This effect stems from the presence of an electron–phonon coupling constant smaller than the sum of the Coulomb pseudopotential and electron-antiferromagnetic spin density fluctuations coupling constant in the interband channel. The resulting superconductive state is an example of extended s-wave pairing with a sign reversal of the order parameter between different Fermi surface sheets.