AN ENHANCED PERTURBATIONAL STUDY ON SPECTRAL PROPERTIES OF THE ANDERSON MODEL

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 loca l spin degeneracy). The finite-temperature impurity density of states (DOS) and the spin-fluctuation spectra are calculated exactly up to th e order O(1/N-2). The presented conserving approximation goes well bey ond the 1/N approximation (NCA) and maintains local Fermi-liquid prope rties down to very low temperatures. The position of the low-lying Abr ikosov-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 verte x corrections. The width and height of the ASR are governed by the uni versal low-temperature energy scale TK. Temperature and degeneracy N d ependence of the static magnetic susceptibility is found to be in exce llent agreement with the Bethe ansatz results. Threshold exponents of the local propagators are discussed, The resonant level regime (N = 1) and intermediate-valence regime (\epsilon(f)\ < Delta) of the model a re thoroughly investigated as a critical test of the quality of the ap proximation. Some applications to the Anderson lattice model are point ed out.