Two Anderson impurities in the framework of the non-crossing approximation: Spectral functions and spin correlations

Using a novel slave boson mapping, which was recently proposed by us for two Anderson impurities embedded in a metal, we present here spectral functions for all pseudoparticles involved in the mapping. These were numerically calculated in the framework of the Non-Crossing Approximation for different temperatures and inter-impurity distances, both for the degenerate (N_f = 6) and nondegenerate (N_f = 2) models. For the nondegenerate case, temperature dependencies of the partial occupancies and the spin-spin correlation function suggest that an antiferromagnetic (AFM)-like ground state is formed at suitable inter-impurity separation. By contrast, Kondo quenching of the impurity moments takes place for the isotropic N_f = 6 case even when a direct AFM interaction is introduced in order to amplify the indirect (inherent) one. Numerical calculations are in agreement with our previous prediction [Phys. Rev. B 47, 14,297 (1993)] that no AFM-like ground state can appear for two isotropic degenerate impurities.