Kondo versus antiferromagnetic ground state of two Anderson impurities.

A slave-boson formulation of the Anderson model for two degenerate impurities with infinite on-site Coulomb interaction U is presented. The Hamiltonian has many features in common with the slave-boson Hamiltonian for the single Anderson impurity but with finite U. It is shown within the noncrossing approximation that in the absence of any anisotropy an antiferromagneticlike ground state is impossible for N f >2. In order to make it possible one must either include anisotropy or add an explicit antiferromagnetic exchange term to the original Anderson model