An enhanced perturbational study on spectral properties of the Anderson model

Abstract

The infinite-U single-impurity Anderson model for rare earth alloys is examined with a new set of self-consistent coupled integral equations, which can be embedded in the large-N expansion scheme (N is the local spin degeneracy). The finite-temperature impurity density of states (DOS) and the spin-fluctuation spectra are calculated exactly up to the order O(1/N2). The presented conserving approximation goes well beyond the 1/N approximation (NCA) and maintains local Fermi-liquid properties down to very low temperatures. The position of the low-lying Abrikosov-Suhl resonance (ASR) in the impurity DOS is in accordance with Friedel's sum rule. For N=2 its shift toward the chemical potential, compared to the NCA, can be traced back to the influence of the vertex corrections. The width and height of the ASR are governed by the universal low-temperature energy scale TK. Temperature and degeneracy N dependence of the static magnetic susceptibility is found to be in excellent agreement with the Bethe ansatz results. Threshold exponents of the local propagators are discussed. The resonant level regime (N=1) and intermediate-valence regime ( mod epsilon f mod < Delta ) of the model are thoroughly investigated as a critical test of the quality of the approximation. Some applications to the Anderson lattice model are pointed out.