FT-IR evaluation of SmFeAsO$_{1-x}$F$_{x}$ (x = 0, 0.069)

Optical properties of superconducting SmFeAsO$_{1-x}$F$_{x}$ (x=0, 0.069) were demonstrated by reflection measurement with FT- IR method. Polycrystalline SmFeAsO$_{1-x}$F$_{x}$ samples were synthesized using two-step solid state reaction described elsewhere [New J. Phys.\textbf{12}, 033005 (2010)]. Purity of samples was checked by X-ray diffraction patterns using Cu K- alpha radiation. The reflection measurement was performed at the range from 9000 cm$^{-1}$ to 18000 cm$^{-1}$ that was corresponded to an energy region from 1.12 eV to 2.25 eV. A photoconductivity of SmFeAsO$_{1-x}$F$_{x}$ was determined by Kramer-Kroning (KK) relation. Reflectivity and photoconductivity measurements, as well as by FT-IR, at various areas were performed to define an energy level of materials [EPL, \textbf{84} 67013 (2008), and J. Phys. Soc. Jpn. \textbf{80} 013707 (2011)]. Obtained photoconductivity and reflection spectra were similar to those of LaFeAsO$_{1-x}$F$_{x}$ that was a basic compound of LnFeAsO$_{1-x}$F$_{x}$ (Ln=La, Ce, Sm), reported by Z. G. Chen et al [Phys. Rev. B \textbf{81}, 100502 (2010)]. Our result suggests that the energy band structure of SmFeAsO was affected by F-doping even in visible area. Details and temperature dependence of the reflection and photoconductivity spectra will be presented at the conference.