Interplay between the mesoscopic Stoner and Kondo effects in quantum dots

TL;DR

This paper explores how ferromagnetic interactions among electrons in a quantum dot influence the Kondo effect, revealing a regime where Kondo correlations are enhanced near the Stoner transition, with unique responses to magnetic fields.

Contribution

It demonstrates the interplay between Stoner ferromagnetism and the Kondo effect in quantum dots, identifying a regime with enhanced Kondo correlations near the Stoner transition.

Findings

Enhanced Kondo correlations near the Stoner transition

Zeeman field increases the Kondo scale in the Stoner regime

Transition to spin-polarized impurity state

Abstract

We consider electrons confined to a quantum dot interacting antiferromagnetically with a spin-$\half$ Kondo impurity. The electrons also interact among themselves ferromagnetically with a dimensionless coupling $\tilde{J}$, where $\tilde{J}=1$ denotes the bulk Stoner transition. We show that as $\tilde{J}$ approaches 1 there is a regime with enhanced Kondo correlations, followed by one where the Kondo effect is destroyed and impurity is spin polarized opposite to the dot electrons. The most striking signature of the first, Stoner-enhanced Kondo regime, is that a Zeeman field increases the Kondo scale, in contrast to the case for noninteracting dot electrons. Implications for experiments are discussed.