Asymmetry-induced effects in Kondo quantum dots coupled to ferromagnetic leads

TL;DR

This paper investigates how asymmetries in contact and material properties affect spin-resolved transport and the Kondo effect in quantum dots coupled to ferromagnetic leads, revealing suppression mechanisms and deriving exchange field formulas.

Contribution

It provides a detailed analysis of asymmetry effects on the Kondo regime in ferromagnetic quantum dots using numerical and perturbative methods, including new formulas for exchange fields.

Findings

Kondo effect is suppressed in parallel configuration due to exchange field.

Asymmetry can suppress the Kondo resonance in antiparallel configuration.

Derived general formulas for exchange fields in different magnetic configurations.

Abstract

We study the spin-resolved transport through single-level quantum dots strongly coupled to ferromagnetic leads in the Kondo regime, with a focus on contact and material asymmetry-related effects. By using the numerical renormalization group method, we analyze the dependence of relevant spectral functions, linear conductance and tunnel magnetoresistance on the system asymmetry parameters. In the parallel magnetic configuration of the device the Kondo effect is generally suppressed due to the presence of exchange field, irrespective of system's asymmetry. In the antiparallel configuration, on the other hand, the Kondo effect can develop if the system is symmetric. We show that even relatively weak asymmetry may lead to the suppression of the Kondo resonance in the antiparallel configuration and thus give rise to nontrivial behavior of the tunnel magnetoresistance. In addition, by using the second-order perturbation theory we derive general formulas for the exchange field in both magnetic configurations of the system.