s±-like spin resonance in the iron-based nodal superconductor BaFe2(As0.65P0.35)2 observed using inelastic neutron scattering

We performed inelastic neutron scattering on a powder sample of iron-based superconductor BaFe2(As0.65P0.35)(2) with T-c = 30 K. Although this system is expected to have line nodes in its superconducting order parameter, we have observed spin resonance at the same scattering vector as that appearing in the s(+/-)-wave iron-based superconductors without line nodes. Moreover, the resonance enhancement, which can be a measure of the area of sign reversal between the hole and electron Fermi surfaces (FSs), is comparable to those without line nodes. These facts indicate that the sign reversal between the FSs is still dominant in this system, and the line nodes should create only a limited area of sign reversal on a single FS. Hence the system can hold higher Tc than the other iron-based superconductors with nodal symmetry, such as LaFePO1-y and KFe2As2 (T-c < 10 K). Comparison with theoretical calculation indicates horizontal line nodes may be a candidate for reproducing the observation.