On the Phase Diagram of Ferropnictides

A model three-band superconductor is considered, in which two hole bands interact with an electron band through the interband spin-fluctuation interaction. For different band fillings and pairing anisotropy, the structure of the superconducting state of such a superconductor is investigated as a function of the ratio of the interband to intraband interaction, considered as an analogue of the doping dependence in ferropnictides. Such a model is shown to well describe the doping evolution of the properties of superconducting ferropnictides, in particular, the characteristic transformation of the electronic specific heat with a change in doping and the anomalous temperature dependence of the dominant superconducting gap for the electron band with the lowest filling and strong anisotropy of intraband pairing. Taking into account the strong coupling corrections, the proposed model can be applied to quantitatively estimate the correlation effects and the magnitude of the nonphonon contribution to the superconductivity of ferropnictides.