Orbital anisotropy of Kondo ions

The striking differences which are often observed in the behaviour of unstable ions with the same valence can be traced to different orbital splittings. This suggestion is discussed in terms of a degenerate Anderson model which is treated in the single ion non-crossing approximation (NCA). Using analytical methods to solve the NCA equations of the anisotropic model the parametrization of the theory is made transparent and the numerical solution of the NCA atT=0 is simplified considerably. The influence of a low ground state degeneracy of the magnetic impurity on the drop of the Kondo temperature is emphasized. Numerical results for the NCA equations are given for a cerium impurity with either a doublet or a quartet ground state. Comparison with the mean field solution of the anisotropic model is made.