We have studied the photoemission spectra of perovskite-type ${\mathrm{Ti}}^{3+}$ and ${\mathrm{V}}^{4+}$ oxides, which have formally the ${\mathit{d}}^1$ configuration ranging from a Mott insulator to a paramagnetic metal. The results indicate that as the Mott-Hubbard gap closes, spectral weight is transferred from the upper and lower Hubbard bands to the region near the Fermi level with decreasing U/W (U,d-d Coulomb repulsion energy; W, one-electron d-band width), i.e., from the incoherent to the coherent part of the single-particle spectral function.

We present an experimental manifestation of how the single-particle density of states around the Fermi level $\left(E_F\right)$ changes near a Mott transition. In a metallic perovskite-type ${3d}^1$ Mott-Hubbard system ${\mathrm{Ca}}_{1-x}{\mathrm{Sr}}_x{\mathrm{VO}}_3$, as one decreases $x$ the spectral weight of the coherent band near $E_F$ is gradually transferred to that of the precursor of the lower Hubbard band $\sim$2 eV below $E_F$. The momentum dependence of the quasiparticle self-energy and hence the long-range exchange or correlation is shown to become progressively important as one approaches the Mott transition from the metallic side.

The electronic structure of ${\mathrm{La}}_{\mathit{x}}$ ${\mathrm{Sr}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{TiO}}_3$ has been studied by photoemission and x-ray absorption spectroscopy. Electron doping through La substitution induces a new photoemission feature of Ti 3d character within the band gap of ${\mathrm{SrTiO}}_3$; the Fermi level is located near the bottom of the conduction band of ${\mathrm{SrTiO}}_3$. The experimental results are incompatible with the rigid-band behavior predicted by one-electron band theory or Hubbard-model calculations.

The phonon dynamics of filled skutterudite CeRu4Sb12 have been studied at room temperature by inelastic neutron scattering. Optical phonons associated with a large vibration of Ce atoms are observed at a relatively low energy of E = 6 meV, and show anticrossing behavior with acoustic phonons. We propose that the origin of the low lattice thermal conductivity in filled skutterudites can be attributed to intensive Umklapp scattering originating from low-lying optical phonons. By an analysis based on a Born-von Karman force model, the longitudinal force constants of the nearest Ce-Sb and Ce-Ru pairs are estimated to be 0.025 mdyn/A, while that of the nearest Ru-Sb pair is estimated to be 1.4 mdyn/A, indicating that the Ce atoms are bound very weakly to the surrounding rigid RuSb6-octahedron cages.Comment: 4pages, 5 figures, J. Phys. Soc. Jpn. (2006) in pres

We have measured photoemission and oxygen $1s$ x-ray absorption spectra of the ferromagnetic metal ${\mathrm{SrRuO}}_3$ and compared them with a first-principles band-structure calculation. The overall distribution of Ru $4d$ and O $2p$ spectral weight is in good agreement with that predicted by the band-structure calculation. However, the observed spectral line shape of the Ru $4d$ band is spread over a wide energy range and the emission intensity at the Fermi level is weakened compared to the band-structure calculation. This implies the importance of electron correlation in the Ru oxide.