Competition between Hund-Rule Coupling and Kondo Effect

We investigate a problem about the competition between the hybridization and the Hund-rule coupling by applying the Wilson numerical renormalization-group method to the extended Kondo model where the impurity spin interacts via the Hund-rule coupling, with an extra spin which is isolated from the conduction electrons. It is shown that the Hund-rule coupling is an irrelevant perturbation against the strong coupling fixed point. However, the Hund-rule coupling decreases the characteristic energy $T_K$ drastically to the lower side and the irrelevant operator, which describes the low energy physics, takes a form of ferromagnetic exchange interaction between the extra spin and the Kondo resonance states because of the existence of the Hund-rule coupling.