Neutron scattering of iron-based superconductors

Shamoto, Shinichi  ; Wakimoto, Shuichi  ; Kodama, Katsuaki   ; Ishikado, Motoyuki; Christianson, A. D.*; Lumsden, M. D.*; Kajimoto, Ryoichi  ; Nakamura, Mitsutaka   ; Inamura, Yasuhiro; Arai, Masatoshi; Kakurai, Kazuhisa; Esaka, Fumitaka  ; Iyo, Akira*; Kito, Hijiri*; Eisaki, Hiroshi*

We have studied low-energy spin excitations on polycrystalline LaFeAsOF samples by inelastic neutron scattering. The dynamical spin susceptibility ''() of the superconducting samples is found to be comparable to that of the magnetically ordered parent sample. On the other hand, ''() almost vanishes at x=0.158, where the superconducting transition temperature T is suppressed to 7 K. This suggests that the low energy spin excitations are closely connected with high-T superconductivity. The disappearance of the spin excitations at low energy would correspond to the disappearance of the hole Fermi surface as the electron concentration increases with doping, as observed in ARPES measurements of BaFeCoAs at x=0.15. The relationship between the spin excitation and the Fermi surface will be discussed in comparison with other iron-based superconductors.