Doping-induced changes in the electronic structure of ${\mathrm{La}}_{\mathit{x}}$${\mathrm{Sr}}_{1\mathrm{-}\mathit{x}}$${\mathrm{TiO}}_3$: Limitation of the one-electron rigid-band model and the Hubbard model

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.