Neutron inelastic scattering peak by dissipationless mechanism in the s₊₊-wave state in iron-based superconductors

We investigate the neutron scattering spectrum in iron pnictides based on the random-phase approximation in the five-orbital model with a realistic superconducting (SC) gap, Δ=5meV. In the normal state, the neutron spectrum is suppressed by large inelastic quasiparticle (QP) scattering rate γ^*∼Δ. In the fully-gapped s-wave state without sign reversal (s₊₊), a hump-shaped enhancement appears in the neutron spectrum just above 2Δ, since the inelastic QP scattering is prohibited by the SC gap. That is, the hump structure is produced by the dissipationless QPs for QP energy E_k<3Δ. The obtained result is more consistent with experimental spectra, compared to the results of our previous paper with Δ=50 meV. On the other hand, both height and weight of the resonance peak in the fully-gapped s-wave states with sign reversal (s _±) are much larger than those observed in experiments. We conclude that the experimentally observed broad spectral peak in iron pnictides is created by the present "dissipationless mechanism" in the s ₊₊-wave state.