Spin excitations in iron oxypnictide superconductor system

鉄ヒ素酸化物超伝導体系のスピン励起

社本 真一  ; 石角 元志; 脇本 秀一  ; 樹神 克明   ; 梶本 亮一  ; 新井 正敏; 福田 竜生  ; 中村 博樹  ; 町田 昌彦  ; 永崎 洋*

Shamoto, Shinichi; Ishikado, Motoyuki; Wakimoto, Shuichi; Kodama, Katsuaki; Kajimoto, Ryoichi; Arai, Masatoshi; Fukuda, Tatsuo; Nakamura, Hiroki; Machida, Masahiko; Eisaki, Hiroshi*

The spin excitations in the LaFeAsOF system have been studied by inelastic neutron scattering measurements with powder samples. In the parent compound, the spin excitation was observed as a magnetic rod at (, , ) in the downfolded tetragonal Brillouin zone. It persisted even in the tetragonal phase at = 280 K. In the superconducting compounds with = 0.057 and 0.082, the spin excitations developed below the superconducting transition temperatures up to the same order of magnitude as that in the parent compound, and they were peaked at about 11 meV. The spin excitation, however, almost disappeared in an overdoped compound with = 0.158, which exhibited only filamentary superconductivity below 7 K. These results indicate that the present superconductivity intimately correlates with the spin fluctuation possibly in relation to the nesting condition between the Fermi surfaces at and M points.