Orbital dependence in kondo effect enlarged by Hund's-rule coupling

The effect of the Hund's-rule coupling on the Kondo effect is studied in connection with the nature of renormalized quasiparticles. Applying the Wilson numerical renormalization-group method, we investigate a system where two localized electrons at impurity site hybridize with conduction electrons with different strength. It is shown that two characteristic energy scales, T-K1 and T-K2, (T-K1 > T-K2) exist irrespective of the existence of the Hund's-rule coupling due to the orbital dependence of hybridizations. As the Hund's-rule coupling is switched on and increased, the ratio between two characteristic energy scales is much more enhanced with both being decreased. We find widely a region of parameters in which T-K2 cannot be seen in the temperature range accessible by experiments. Practically, the system shows a new type of itinerant-localized duality where one of two localized electrons forms local Fermi liquid with conduction electrons and the other remains as a localized spin. The case of antiferromagnetic Hund's-rule coupling is also discussed. It is shown Chat the low energy effective Hamiltonian is described by the same form irrespective of a sign of the Hund's-rule coupling.