HYBRIDIZATION VERSUS LOCAL EXCHANGE INTERACTION IN THE KONDO PROBLEM - A 2-BAND MODEL

The competition between local exchange and hybridization in Kondo syst ems is investigated by studying a model in which a localized spin 1/2 has an exchange interaction with two bands with a ferromagnetic coupli ng J(sf) > 0 and an antiferromagnetic coupling J(hyb) < 0, respectivel y. It is shown that a Kondo effect takes place even for large values o f the ratio \J(sf)/J(hyb)\. The results should be applicable to real s ystems when orbital degeneracy is taken into account, and indicate tha t the Kondo effect can occur even in the presence of a strong local ex change. Consequences on the picture of the competition between the two effects are discussed.