Two distinct resonance-like excitations in underdoped Ba_K_Fe_As_ (x = 0.25) as seen via inelastic neutron scattering

Murai, Naoki  ; Kajimoto, Ryoichi  ; Ikeuchi, Kazuhiko*; Tanaka, Kiyohisa*; Nakajima, Masamichi*; Ideta, Shinichiro*; Suzuki, Katsuhiro*

We report an inelastic neutron scattering (INS) study of underdoped Ba_K_Fe_As_ that shows the presence of double-resonance at the same commensurate wave vector in the superconducting (SC) state. By comparing our INS data with the SC gap structure of the same crystal, as measured by angle-resolved photoemission spectroscopy (ARPES), we show that the observed double-resonance feature originates neither from SC gap anisotropy nor from multiple SC gaps on different Fermi-surface sheets. This suggests that the double-resonance feature in iron-pnictides cannot be interpreted within a spin-exciton scenario.