Effect of a Variable-Spin Quantum Dot on a Wire Conductance

A numerically exact calculation of the T=0 transport properties of a quantum wire interacting with a lateral two-level quantum dot is presented. The wire conductance is calculated for all different states of charge and spin of the quantum dot. For a dot with two electrons we obtain an enhancement of the Kondo temperature at the singlet-triplet transition and a non-universal scaling law for its dependence upon the dot energy spacing. We find that the Kondo correlation is stronger for a dot spin $S_D \sim 1$ than for $S_D \sim 1/2$. In both cases the wire current is totally quenched by the Kondo effect. When the dot is in the mixed-valence regime and $1/2 < S_D < 1$ the wire conductance is partially quenched except in a very small region of gate potential where it reaches the maximum value $e^2/h$.