A complete Bethe ansatz solution of the $\mathrm{SU}(N)\ifmmode\times\else\texttimes\fi{}\mathrm{SU}(f)$ Coqblin-Schrieffer model and a detailed analysis of some physical applications of the model 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 \ensuremath{\mu}. For $\ensuremath{\mu}=f,$ we find a Fermi-liquid fixed point, with the impurity spin completely screened. For $f>\ensuremath{\mu},$ the impurity is overscreened and the model has NFL properties. The form the NFL behavior takes depends on the
N and
f: for
N< f, the specific heat and the susceptibility are dominated by the NFL contributions; for
N>f the leading contributions are Fermi-liquid-like, and the NFL behavior can be seen only to subleading order; and for
N=f the behavior is marginal. We also analyze the possibility of physical realizations. We show by a detailed renormalization-group and
1/f analysis that the tunneling
N-state problem can be mapped into the $\mathrm{SU}(N)\ifmmode\times\else\texttimes\fi{}\mathrm{SU}(f)$ exchange model, and discuss the subtle differences between the two models. As another physical realization we suggest a double quantum dot structure that can be described by means of an $\mathrm{SU}(3)\ifmmode\times\else\texttimes\fi{}\mathrm{SU}(2)$ model if the parameters of the dots are tuned appropriately.
Numerical renormalization-group results on entropy of the anisotropic two-channel Kondo model with the band-width cutoff (
D) in the presence of a magnetic field (
h) are obtained to determine crossover temperature from the non-Fermi liquid to Fermi liquid fixed point. It is found that the crossover temperature (
Tx) is given by
Tx≡rTK∼D(ΔJ/Jav)2e−1/Jav when $(h /T_{\rm K})^2 \ll r \ll 1 $, where
TK,
Jav and
ΔJ are the Kondo temperature, the average and difference of the exchange coupling constants, respectively. This result indicates that non-Fermi liquid behavior can be seen even if
ΔJ>TK. Robust similarities of the crossover behavior in the region around the non-Fermi liquid critical point to that of the two-impurity Kondo model are also discussed.