Spectral functions in doped transition metal oxides

We present experimental photoemission and inverse photoemission spectra of SrTiO3−δ representing electron doped d 0 systems. Photoemission spectra in presence of electron doping exhibit prominent features arising from electron correlation effects, while the inverse photoemssion spectra are dominated by spectral features explainable within single-particle approaches. We show that such a spectral evolution in chemically doped correlated systems is not compatible with expectations based on Hubbard or any other similar model. We present a new theoretical approach taking into account the inhomogeneity of the real system which gives qualitatively different results compared to standard homogeneous models and is in quantitative agreement with experiments. PACS numbers: 79.60.Bm, 79.60.Ht, 71.30.+h Typeset using REVTEX