KONDO EFFECT DUE TO IMPURITIES WITH (5F)(N) CONFIGURATION - FERMI-LIQUID VERSUS NON-FERMI LIQUID

The Kondo effect due to U-type impurities is studied in connection with the stability of the Fermi liquid and the non-Fermi liquid. First, an effective exchange Hamiltonian in terms of irreducible tensor operators is derived for conduction electrons, which are coupled with plural 5f electrons. It is based on the assumption of strong spin-orbit and Hund couplings. Second, a model for f(2) configuration placed in a tetragonal or hexagonal crystal held is studied by simplifying the internal structure as the non-Kramers doublet ground slate and the first singlet excited state. The numerical renormalization group analysis shows that the singlet excited state plays an important role to stabilize the Fermi liquid over the non-Fermi liquid. Third, the difference of the Kondo effect is examined between non-Kramers doublet for f(2) and Kramers doublet for f(3) in the presence of the cubic crystal field. It is shown that for f(3) the Hund coupling reduces the channel number to one, while the situation is different for f(2).