Evolution of the spectral function in Mott-Hubbard systems with ${\mathit{d}}^1$ configuration

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.