NRG study of the Kondo effect in the presence of itinerant-electron ferromagnetism

TL;DR

This study uses the numerical renormalization group method to analyze how ferromagnetic leads affect the Kondo effect in quantum dots, revealing spin-splitting suppression and conditions for its restoration.

Contribution

It demonstrates how ferromagnetic electrodes induce spin-splitting in quantum dots and shows that the Kondo effect can be recovered with a magnetic field, maintaining a Fermi liquid ground state.

Findings

Spin-splitting suppresses the Kondo effect in ferromagnetic leads.

Applying a magnetic field can restore the Kondo resonance.

Transport remains spin-independent in the unitary limit.

Abstract

The Kondo effect in quantum dots (QDs) - artificial magnetic impurities - attached to ferromagnetic leads is studied with the numerical renormalization group (NRG) method. It is shown that the QD level is spin-split due to presence of ferromagnetic electrodes, leading to a suppression of the Kondo effect. We find that the Kondo effect can be restored by compensating this splitting with a magnetic field. Although the resulting Kondo resonance then has an unusual spin asymmetry with a reduced Kondo temperature, the ground state is still a locally-screened state, describable by Fermi liquid theory and a generalized Friedel sum rule, and transport in the unitary limit is not spin dependent.