Impurity states in Mott insulators

Abstract

The effect of a point scattering potential on the properties of a nearly half filled narrow energy-band is studied in the limit of strong intra-atomic Coulomb repulsions. The potential needed to localize a state depends on the spin configuration. A localized hole is found to stabilize a ferromagnetic polarization within a few atomic distances from the impurity. The strength of this coupling, which decreases as an inverse power of the bound state energy and exponentially with distance, is evaluated. The effect of a magnetic field on the bound state energy is studied. A large negative magnetoresistance is predicted, and a metal-insulator transition is shown to be possible for a certain range of impurity potentials, and impurity concentrations. The experimental situation in NiO and Li doped NiO is discussed