Spectral functions in doped transition metal oxides

Abstract

We present experimental photoemission and inverse photoemission spectra of SrTiO_{3 − δ} representing electron-doped d⁰ systems. Photoemission spectra in the presence of electron doping exhibit prominent features arising from electron correlation effects, while the inverse photoemission 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.