1/(N-1) expansion based on a perturbation theory in U for the Anderson model with N-fold degeneracy

TL;DR

This paper develops a 1/(N-1) expansion method for the N-fold degenerate Anderson model, providing accurate predictions of low-energy properties and Kondo transport, validated against numerical results for N=4.

Contribution

It introduces a perturbation theory based on a 1/(N-1) expansion for the Anderson model with N-fold degeneracy, enabling reliable analysis for N > 4.

Findings

Wilson ratio closely matches NRG results at N=4

The approach accurately predicts Kondo state properties

Reliable results for nonequilibrium transport in quantum dots

Abstract

We study low-energy properties of the N-fold degenerate Anderson model. Using a scaling that takes u=(N-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-1). We calculate the renormalized parameters, which characterize the Kondo state, to the next leading order in the 1/(N-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.