Optical Study of Metal-Insulator Transition in SmBaCo_2O_<6-δ> Single Crystal : Condensed Matter: Electronic Properties, etc.

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The optical reflectivity spectrum and its temperature dependence were measured on a cleaved (001) surface of SmBaCo_2O_<5.6>. With an increase in temperature, the reflectivity below 1 eV increases up to the metal-insulator transition temperature, T_<MI> = 360 K, and saturates above T_<MI>. The spectrum of optical conductivity σ(ω) shows large variation in temperature which accompanies the transfer of spectral weight between a broad peak around 3 eV, which can be assigned to the O_<2p> - Co_<3d> charge-transfer excitation, and the incoherent excitation of carriers below 1 eV. The transferred spectral weight is as large as 0.17 per Co ion, which implies that the effective mass of an electron, m', can be estimated to be 6m_0. The optical gap of 0.2 eV at 20 K is consistent with the resistivity measurement.
社団法人日本物理学会の論文
2000-11-15