Electron-phonon interactions of Si100 and Ge100 superconductors with Ba atoms inside.

The absolute density of states of isostructural Ba24Si100 and Ba24Ge100 near the Fermi level, which is very relevant for discussion on phonon-mediated superconductivity, is quantitatively evaluated to be 0.28  states  eV⁻¹/Ge  atom and 0.18  states  eV⁻¹/Si   atom by combining soft x-ray photoelectron spectroscopy and magnetic susceptibility measurements.

Preparation and thermoelectric properties of sintered type-I clathrates K8Ga(x)Sn(46-x).

Polycrystalline clathrate samples of nominal K(8)Ga(x)Sn(46-x) were prepared by the spark plasma sintering method to investigate their crystal structures, mobilities and thermoelectric properties. The samples almost had a single-phase type-I clathrate structure, and their relative densities reached as high as 98%. The room-temperature mobility of the K(8)Ga(8)Sn(38) sample was 25 cm(2) V(-1) s(-1), which substantially exceeded the reported mobilities of Rb- and Cs-containing Sn clathrates.

Soft x-ray photoelectron spectroscopy study of type-I clathrates.

Extensive soft x-ray photoelectron spectroscopy studies are performed on Ba Ga Ge (BGG) and SrGaGe (SGG) single crystals ranging from Fermi to core levels, at a high-energy facility. Valence band x-ray photoelectron spectroscopy (XPS) experiments with theoretical calculations revealed that the valence band is mainly constructed by the Ge/Ga 4s and 4p wave functions with little contribution of the Ba/Sr atomic orbitals. Surprisingly, unexpected features evidencing the different shift for the 2a- and 6d- sites between Ba 4d and Sr 3d are observed.