Beyond the Nca: New Results for the Spectral Properties of the Anderson Model

Abstract

In the framework of direct perturbation theory a fully self-consistent approximation beyond the well known NCA will be presented for the Anderson Model. The resummation of a class of skeleton diagrams up to infinite order in $V$ includes all contribution up to the order $O(1/N^2)$ ( $N$ = degeneracy of the magnetic state). Qualitative improvements in maintaining local Fermi-Liquid relations and one-particle spectral properties in comparison to the well known NCA will be reported. The location and temperature dependence of the AS-resonance for the case $N=2$ is found to be rather close to the chemical potential in excellent agreement with Friedel's sum rule; the static magnetic susceptibility exhibits the same $N$-dependence as the exact {\em Bethe-Ansatz} solution.