Integrable model for two interacting magnetic impurities with Γ8 ground multiplet

A model for two Kondo impurities with a fourfold degenerate ground multiplet interacting via the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction is considered. The system is the integer-valent limit of a hybridization model in which electrons are localized (delocalized) in pairs (one at each impurity). The model is mapped onto the Bethe Ansatz solution of the single SU(N) Anderson impurity in the U→∞ limit. The RKKY interaction is introduced a posteriori as a splitting of the manifold. The occupation of spin states with even and odd parities, the homogeneous and staggered magnetic (and quadrupolar) field susceptibilities, the specific-heat γ coefficient, and the Wilson ratio are studied for the ground state as a function of the ratio of RKKY coupling strength to Kondo temperature. The motivation for this calculation is the rich phase diagram of the alloy series (Ce,La)B6. copyright 1999 The American Physical Society