Isotope effect and the role of phonon in the Fe-based superconductors

Abstract

We studied the isotope effect of phonon in the Fe-based superconductors using a phenomenological two band model for the sign-changing s-wave ($\pm$s-wave) state. Within this mean-field model, we showed that the large isotope effect is not inconsistent with the $\pm$s-wave pairing state and its high transition temperature. In principle, a large phonon isotope coefficient $\alpha$ implies a large phonon coupling constant. However, the asymmetric density of states (DOS) between two bands substantially enhances the value of $\alpha$, so that a moderate value of the phonon coupling constant (${\lambda }_{\mathrm{ph}}\approx 0.4$) can produce a very large value of $\alpha$ ($\approx 0.4$) as well as a high transition temperature together with an antiferromagnet (AFM)-induced interaction.

arXiv comment5 pages, 2 figures

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• Model for the inverse isotope effect of FeAs-based superconductors in the $\pi$-phase-shifted pairing state
• Brief review on iron-based superconductors: are there clues for unconventional superconductivity?
• Influence of multiorbitals and anisotropic Coulomb interactions on isotope effect coefficient in doped Fe-based superconductors