The Kondo problem of systems with two-electron occupancy in a realistic crystalline electric field (CEF) is investigated using the numerical renormalization group method. We examine the ground state of an impurity Anderson model, which has a singlet as the lowest state and multiplets as excited states of an f 2 configuration subject to a cubic CEF. When the hybridization between the f electrons and the conduction electrons is small, the ground state is a CEF-like singlet state. For a large hybridization, on the other hand, the ground state becomes a Kondo-like singlet state. The hybridization with Γ8 symmetry plays an important role in the Kondo effect in this model. The transition between the two types of singlet states is accompanied by a lowering of the energy scale when the Γ8 type hybridization is relatively large. The non-Fermi liquid behavior of a model, which has a non-Kramers lowest state of an f 2 configuration subject to the tetragonal CEF, is also investigated.
- Crystalline electric field
- Impurity Anderson model
- Kondo effect
- Numerical renormalization group