Neutron-scattering study of the oxypnictide superconductor LaFeAsO0.87F0.13

The recently discovered superconductor LaO0.87F0.13FeAs (T-C approximate to 26 K) was investigated using the neutron-scattering technique. No spin-density-wave (SDW) order was observed in the normal state or in the superconducting state, both with and without an applied magnetic field of 9 T, consistent with the proposal that SDW and superconductivity are competing in the laminar materials. While our inelastic measurements offer no constraint on the spin dynamic response from a d-wave pairing, an upper limit for the magnetic-resonance peak predicted from an extended s-Wave pairing mechanism is provided. Our measurements also support the energy scale of the calculated phonon spectrum, which is used in the electron-phonon coupling theory and fails to produce the high observed T-C.