Suppression of the Kondo Effect in Quantum Dots by Even-Odd Asymmetry

TL;DR

This paper investigates how even-odd electron number asymmetry and spin-exchange interactions influence the Kondo effect in quantum dots, revealing suppression in certain conditions and matching experimental conductance patterns.

Contribution

It introduces a model including spin-exchange interactions and demonstrates their impact on the Kondo effect and conductance periodicity in quantum dots.

Findings

Kondo effect occurs only with odd electron numbers for antiferromagnetic J_d.

Spin-exchange causes a second conductance period.

Ferromagnetic J_d recovers S=1 Kondo behavior.

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.