Observation of Softened Fe Modes in K-Doped BaFe2As2 via Fe-57 Nuclear Resonant Inelastic Scattering

The contribution of Fe atomic motion to the superconductivity in the K-doped BaFe2As2 system was investigated by Fe-57 nuclear resonant inelastic scattering. A significant K-doping effect was observed in the Fe partial phonon density of states. The present results indicate that low-lying Fe optical modes are softened by K-doping. This demonstrates that the Fe atomic motion correlates with the superconductivity in K-doped BaFe2As2.