Ferromagnetic Kondo effect in a triple quantum dot system

TL;DR

This paper proposes a triple quantum dot device to realize and study the ferromagnetic Kondo effect, including its transition to antiferromagnetic behavior, using numerical renormalization group analysis.

Contribution

It introduces a simple quantum dot setup to explore the ferromagnetic Kondo model and its transition to antiferromagnetic Kondo effect through detailed numerical simulations.

Findings

Identification of non-analytic zero-bias anomaly

Sensitivity of the system to magnetic fields

Observation of the transition between ferromagnetic and antiferromagnetic Kondo regimes

Abstract

We propose that a simple device of three laterally-coupled quantum dots, the central one contacted by metal leads, can realize the ferromagnetic Kondo model, which is characterized by interesting properties like a non-analytic inverted zero-bias anomaly and an extreme sensitivity to a magnetic field. Furthermore, by tuning the gate voltages of the lateral dots, this device may allow to study the transition from ferromagnetic to antiferromagnetic Kondo effect, a simple case of a Berezinskii-Kosterlitz-Thouless transition. We model the device by three coupled Anderson impurities that we study by numerical renormalization group. We calculate the single-particle spectral function of the central dot, which at zero frequency is proportional to the zero-bias conductance, across the transition, both in the absence and in the presence of a magnetic field.