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We report a resonant inelastic x-ray scattering (RIXS) study of charge excitations in the electron-doped high-T(c) superconductor Nd1.85 Ce0.15 CuO4. The intraband and interband excitations across the Fermi energy are separated for the first time by tuning the experimental conditions properly to measure charge excitations at low energy. A dispersion relation with q-dependent width emerges clearly in the intraband excitation, while the intensity of the interband excitation is concentrated around 2 eV near the zone center. The experimental results are consistent with theoretical calculation of the RIXS spectra based on the Hubbard model.

We report the electrical resistivity , Hall coefficient R H , thermoelectric power S, specific heat C, and thermal conductivity on single crystals of the type-VIII clathrate Ba 8 Ga 16 Sn 30 grown from Sn-flux. Negative S and R H over a wide temperature range indicate that electrons dominate electrical transport properties. Both ͑T͒ and S͑T͒ show typical behavior of a heavily doped semiconductor. The absolute value of S increases monotonically to 243 V / K with increasing temperature up to 550 K. The large S may originate from the low carrier concentration n = 3.7ϫ 10 19 cm −3 . Hall mobility H shows a maximum of 62 cm 2 / V s around 70 K. The analysis of temperature dependence of H suggests a crossover of a dominant scattering mechanism from ionized impurity to acoustic phonon scattering with increasing temperature. The existence of local vibration modes of Ba atoms in cages composed of Ga and Sn atoms is evidenced by analysis of experimental data of structural refinement and specific heat, which give an Einstein temperature of 50 K and a Debye temperature of 200 K. This local vibration of Ba atoms should be responsible for the low thermal conductivity ͑1.1 W / m K at 150 K͒. The potential of type-VIII clathrate compounds for thermoelectric application is discussed.

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