Stability of Non-Fermi Liquid in Kondo Effect due to (5f)2Configuration

Abstract

The stability of the non-Fermi liquid (NFL) in Kondo effect is studied by considering the excited states of the 5 f -electrons. First, in order to examine their effects in the strong correlation limit, the exchange model is derived for a tetragonal crystal field by restricting the localized states in f 2 to a non-Kramers doublet and a singlet; all the states are taken into account for f 1 . The numerical renormalization group analysis for this model shows that the singlet state in f 2 and one of the excited states in f 1 play an important role to stabilize the Fermi liquid (FL) over the NFL. Second, the same problem is examined for the six-fold orbitally degenerate Anderson model by considering all the local excited states. The competition between FL and NFL sensitively depends on the Coulomb and Hund couplings, the orbital anisotropy and the hybridization term. The six-fold orbital degeneracy is also important to realize NFL; in fact a similar analysis on the four-fold orbitally degenerate Anderson model...