Spin-resolved electron-phonon coupling in FeSe and KFe2Se2

The effect of the static magnetic moments of iron on electron-phonon interactions in layered FeSe and KFe2Se2 is studied. First-principles techniques based on the pseudopotential density functional approach and the local spin density approximation are utilized to calculate the band structures, phonon dispersions, and electron-phonon coupling properties. Our results indicate that the introduction of iron magnetic moments leads to significant changes in electronic structure induced by Fe 3d states near the Fermi level, to phonon frequency softening for several vibrational modes, and to a dramatic increase in electron-phonon coupling for specific modes. The increase in Brillouin-zone-averaged coupling is about twofold. Our estimates of superconducting transition temperatures based on the McMillan equation yield values closer to experimental results for the spin-resolved case. However, these values are not large enough to explain the observed transition temperature.