  Resonant photoemission at the Ti 2p and O 1s edges on a Nb-doped SrTiO3 thin
film revealed that the coherent state (CS) at the Fermi level (EF) had mainly
Ti 3d character whereas the incoherent in-gap state (IGS) positioned ~1.5 eV
below EF had mixed character of Ti 3d and O 2p states. This indicates that the
IGS is formed by a spectral-weight transfer from the CS and subsequent
spectral-weight redistribution through d-p hybridization. We discuss the
evolution of the excitation spectrum with 3d band filling and rationalize the
IGS through a mechanism similar to that proposed by Haldane and Anderson.
