T-MATRIX FORMULATION OF IMPURITY SCATTERING IN CORRELATED SYSTEMS

Using a generalized T-matrix description which, in principle, exactly includes Coulomb correlations and potential scattering events, resonan t and bound impurity states are discussed. Like in the noninteracting case, the effects of the scattering potential can be divided into diff erent partial-wave channels, exploiting the symmetry of the underlying lattice. Due to Coulomb correlations, bare local (i.e., s-wave) poten tials become dynamic and extended, being responsible also for p-, d-wa ve, etc., scattering effects. Numerically exact results for both the t wo-dimensional t-J and Hubbard models are used to construct a simple ( static) approximation to the effective impurity potential which is sho wn to reproduce the exact resonant scattering and bound states in the relevant symmetry channels.