Fully compensated Kondo effect for a two-channel spin S=1 impurity

We study the low-temperature properties of the generalized Anderson impurity model in which two localized configurations, one with two doublets and the other with a triplet, are mixed by two degenerate conduction channels. By using the numerical renormalization group and the noncrossing approximation, we analyze the impurity entropy, its spectral density, and the equilibrium conductance for several values of the model parameters. Marked differences with respect to the conventional one-channel spin $s=1/2$ Anderson model, which can be traced as hallmarks of an impurity spin $S=1$, are found in the Kondo temperature, the width and position of the charge-transfer peak, and the temperature dependence of the equilibrium conductance. Furthermore, we analyze the rich effects of a single-ion magnetic anisotropy $D$ on the Kondo behavior. In particular, as shown before, for large enough positive $D$ the system behaves as a ``non-Landau'' Fermi liquid that cannot be adiabatically connected to a noninteracting system turning off the interactions. For negative $D$ the Kondo effect is strongly suppressed. While the model is suitable for the description of a single Ni impurity embedded in an O-doped Au chain, it is a generic one for $S=1$ and two channels and might be realized in other nanoscopic systems.