SOLUTION OF THE MULTICHANNEL COQBLIN-SCHRIEFFER IMPURITY MODEL AND APPLICATION TO MULTILEVEL SYSTEMS

A complete Bethe ansatz solution of the SU(N)x SU(f) Coqblin-Schrieffe r model and a detailed analysis of some physical applications of the m odel are given. As in the usual multichannel Kondo model, a variety of Fermi-liquid and non-Fermi-liquid (NFL) fixed points is found, whose nature depends on the impurity representation mu. For mu = f, we find a Fermi-liquid fixed point, with the impurity spin completely screened . For f > mu, the impurity is overscreened and the model has NFL prope rties. The form the NFL behavior takes depends on the N and f: for N l ess than or equal to f, the specific heat and the susceptibility are d ominated by the NFL contributions; for N > f the leading contributions are Fermi-liquid-like, and the NFL behavior can be seen only to suble ading order; and for N = f the behavior is marginal. We also analyze t he possibility of physical realizations. We show by a detailed renorma lization-group and 1/f analysis that the tunneling N-state problem can be mapped into the SU(N)x SU(f) exchange model, and discuss the subtl e differences between the two models. As another physical realization we suggest a double quantum dot structure that can be described by mea ns of an SU(3)x SU(2) model if the parameters of the dots are tuned ap propriately.