Gate-tunable split Kondo effect in a carbon nanotube quantum dot

TL;DR

This paper investigates the split Kondo effect in a carbon nanotube quantum dot, revealing how magnetic field and gate configurations influence the Kondo resonance and suggesting a two-impurity Kondo model with tunable exchange interactions.

Contribution

It provides a detailed experimental analysis of gate-tunable split Kondo effects and introduces a model involving a two-impurity Kondo effect with antisymmetric exchange interactions.

Findings

Splitting decreases with increasing magnetic field, leading to a zero-bias Kondo resonance.

Different gate configurations can prevent the Kondo resonance from reappearing, showing gate-dependent exchange interactions.

Observation of an avoided crossing of high-conductance lines indicating complex spin interactions.

Abstract

We show a detailed investigation of the split Kondo effect in a carbon nanotube quantum dot with multiple gate electrodes. It is found that the splitting decreases for increasing magnetic field, to result in a recovered zero-bias Kondo resonance at finite magnetic field. Surprisingly, in the same charge state, but under different gate-configurations, the splitting does not disappear for any value of the magnetic field, but we observe an avoided crossing of two high-conductance lines. We think that our observations can be understood in terms of a two-impurity Kondo effect with two spins coupled antiferromagnetically. The exchange coupling between the two spins can be influenced by a local gate, and the non-recovery of the Kondo resonance for certain gate configurations is explained by the existence of a small antisymmetric contribution to the exchange interaction between the two spins.