Universality of the Kondo effect in quantum dots with ferromagnetic leads

TL;DR

This paper demonstrates that the Kondo effect in quantum dots with ferromagnetic leads exhibits universal behavior, with a magnetic field-dependent splitting that can be modeled and understood through numerical renormalization group calculations.

Contribution

It shows the universality of the Kondo effect in quantum dots with ferromagnetic leads and provides a simple model to explain experimental observations.

Findings

Kondo resonance splitting depends on tunnel coupling and magnetic field

Magnetoconductance exhibits universal behavior when scaled appropriately

Numerical renormalization group explains the experimental data

Abstract

We investigate quantum dots in clean single-wall carbon nanotubes with ferromagnetic PdNi-leads in the Kondo regime. In most odd Coulomb valleys the Kondo resonance exhibits a pronounced splitting, which depends on the tunnel coupling to the leads and an external magnetic field $B$, and only weakly on gate voltage. Using numerical renormalization group calculations, we demonstrate that all salient features of the data can be understood using a simple model for the magnetic properties of the leads. The magnetoconductance at zero bias and low temperature depends in a universal way on $g \mu_B (B-B_c) / k_B T_K$, where $T_K$ is the Kondo temperature and $B_c$ the external field compensating the splitting.