Inelastic X-ray scattering studies of the phonons on iron-based new superconductors

X線非弾性散乱による鉄系新超伝導物質のフォノンの研究

福田 竜生  ; Baron, A. Q. R.*; 社本 真一  ; 石角 元志; 中村 博樹  ; 町田 昌彦  ; 内山 裕士*; 伊豫 彰*; 鬼頭 聖*; 水木 純一郎; 新井 正敏; 永崎 洋*

Fukuda, Tatsuo; Baron, A. Q. R.*; Shamoto, Shinichi; Ishikado, Motoyuki; Nakamura, Hiroki; Machida, Masahiko; Uchiyama, Hiroshi*; Iyo, Akira*; Kito, Hijiri*; Mizuki, Junichiro; Arai, Masatoshi; Eisaki, Hiroshi*

Recent discovery of a new class of iron-based new superconductors has attracted considerable attraction. In the very early stage calculations of phonon properties appeared and suggested that the superconductivity in these materials are not phonon mediated. Experimentally, however, large isotope effect is observed. Moreover, we carried out inelastic X-ray scattering on some powder as well as single samples with and without superconducting transition at low temperature. All the spectra we investigated have almost the same shape, and the branch around 30meV shows pronounced softening compared to LDA-based phonon calculations. Further investigations on single crystals of PrFeAsO showed no large dependences in doping as well as temperature. However, the spectra are found to agree better with calculations of an orthorhombic magnetic parent material, though the real compounds are non-magnetic and all samples are tetragonal at room temperature.