Suppression of the Kondo Effect in Quantum Dots by Even-Odd Asymmetry
Abstract
We analyze here a model for single-electron charging in semiconductor quantum dots that includes the standard Anderson on-site repulsion (U) as well as the spin-exchange (
J
d
) that is inherently present among the electrons occupying the various quantum levels of the dot. We show explicitly that for ferromagnetic coupling (
J
d
>0
), an s-d exchange for an S=1 Kondo problem is recovered. In contrast, for the antiferromagnetic case,
J
d
<0
, we find that the Kondo effect is present only if there are an odd number of electrons on the dot. In addition, we find that spin-exchange produces a second period in the conductance that is consistent with experimental measurements.