Residual Kondo effect in quantum dot coupled to half-metallic ferromagnets

TL;DR

This paper investigates the Kondo effect in a quantum dot with half-metallic ferromagnetic leads, revealing a residual Kondo resonance in certain configurations and analyzing its characteristics and detectability.

Contribution

It demonstrates that the Kondo effect persists in anti-parallel configurations and identifies a related elastic cotunneling effect in parallel configurations, using advanced Green function techniques.

Findings

Kondo effect is not fully suppressed in anti-parallel lead magnetizations.

A resonance similar to Kondo appears due to elastic cotunneling in parallel configuration.

Minority spin electrons form the resonance, but it is not directly observable in transport measurements.

Abstract

We study the Kondo effect in a quantum dot coupled to half-metallic ferromagnetic electrodes in the regime of strong on-dot correlations. Using the equation of motion technique for nonequilibrium Green functions in the slave boson representation we show that the Kondo effect is not completely suppressed for anti-parallel leads magnetization. In the parallel configuration there is no Kondo effect but there is an effect associated with elastic cotunneling which in turn leads to similar behavior of the local (on-dot) density of states (LDOS) as the usual Kondo effect. Namely, the LDOS shows the temperature dependent resonance at the Fermi energy which splits with the bias voltage and the magnetic field. Moreover, unlike for non-magnetic or not fully polarized ferromagnetic leads the only minority spin electrons can form such resonance in the density of states. However, this resonance cannot be observed directly in the transport measurements and we give some clues how to identify the effect in such systems.