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) = 30 K, 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 ∼ 1.20 Å−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 ∼ 12 meV and a gap below 6 meV. 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 (=30 K) despite the nodal symmetry.

► Inelastic neutron scattering has been performed on BaFe2(As0.65P0.35)2. ► Unexpectedly, we observed spin resonance at Q ∼ 1.2 A−1 and twice enhancement ratio. ► These are similar to other iron-based superconductors with fully-gapped s± symmetry. ► It suggests that fully-gapped s± symmetry dominates in this system. ► This situation makes BaFe2(As0.65P0.35)2 high-Tc (=30 K) despite nodal symmetry.