1/(N−1)expansion based on a perturbation theory inUfor the Anderson model withN-fold degeneracy

Abstract

We study low-energy properties of the $N$-fold degenerate Anderson model. Using a scaling that takes $u=(N\ensuremath{-}1)U$ as an independent variable in place of the Coulomb interaction $U$, the perturbation series in $U$ is reorganized as an expansion in powers of $1/(N\ensuremath{-}1)$. We calculate the renormalized parameters, which characterize the Kondo state, to the next leading order in the $1/(N\ensuremath{-}1)$ expansion at half-filling. The results, especially the Wilson ratio, agree very closely with the exact numerical renormalization group results at $N=4$. This ensures the applicability of our approach to $N>4$, and we present highly reliable results for nonequilibrium Kondo transport through a quantum dot.