Inelastic neutron scattering on iron-based superconductor BaFe2(As,P)2

Inelastic neutron scattering has been performed on powder sample of an iron-based superconductor BaFe2(As0.65P0.35)2 with superconducting transition temperature (Tc)=30K, whose superconducting (SC) order parameter is expected to have line node. In the normal state, constant-E scan of dynamical structure factor, S(Q,E), exhibits a peak structure centered at momentum transfer Q∼1.20Å−1, corresponding to antiferromagnetic wave vector. Below Tc, the redistribution of the magnetic spectral weight takes place, resulting in the formation of a peak at E∼12meV and a gap below 6meV. The enhanced magnetic peak structure is ascribed to the spin resonance mode, evidencing sign change in the SC order parameter similar to other iron-based high-Tc superconductors. It suggests that fully-gapped s± symmetry dominates in this superconductor, which gives rise to high-Tc (=30K) despite the nodal symmetry.