Coulomb localization in orbital degenerate, doped Mott insulators

We study electron localization in a three-band extended Hubbard model describing the t2g electrons of doped vanadium perovskites such as La1−xCaxVO3, where Ca defects are represented by Coulomb potentials. The main goal of this paper is to explore what happens when long-range electron-electron (e-e) interactions are switched on. The electronic structure of these doped Mott-Hubbard insulators is calculated using the unrestricted Hartree-Fock approximation that allows to perform the required statistical averages over many distinct defect realizations. The Mott gap is found to persist up to large doping and the defect states, appearing inside of it, are seen to develop a defect states gap centered at the Fermi energy. The internal kinetic energy of the doped holes, forming spin-orbital polarons bound to the defects, induces the defect states gap even in the absence of e-e interactions. Such kinetic gap survives disorder fluctuations and is amplified by long-range e-e interactions. A study of the inverse participation ratio reveals the small size of such spin-orbital polarons and provides an explanation for the persistence of spin and orbital order up to high doping.