Reappearance of Kondo Effect in Serially Coupled Symmetric Triple Quantum Dots

TL;DR

This paper studies the reemergence of the Kondo effect in a triple quantum dot system, revealing how interdot coupling induces a second Kondo screening and affects spectral and transport properties.

Contribution

It demonstrates the reappearance of the Kondo effect in symmetric triple quantum dots due to interdot coupling, using the hierarchical equations of motion approach.

Findings

Reappearance of Kondo effect leads to a three-peak spectral structure.

Local susceptibility of the middle dot changes sign with coupling strength.

Temperature and coupling influence the Kondo-related transport properties.

Abstract

We investigate the spectral properties of serially coupled triple quantum dot (TQD) system by means of the hierarchical equations of motion (HEOM) approach. We find that with the increase of the interdot coupling t, the first Kondo screening is followed by another Kondo effect reappearing due to the transition from the respective Kondo singlet state of individual QD to the coherence bonding state generated among the three QDs. The reappearance of Kondo effect results in the three-peak structure of the spectral functions of peripheral QD-1(3). By investigating the susceptibility \c{hi}, we find that the local susceptibility of intermediate QD-2 is a positive value at weak interdot coupling, while it changes into negative value at strong interdot coupling, at which the TQD system gives rise to the reappearance of Kondo effect. We also find the slopes of 1/\c{hi} will deviate from straight line behaviour at low temperature in the reappearing Kondo regime. In addition, the influence of temperature T and dot-lead coupling strength {\Delta} on the reappearing Kondo effect as well as the Kondo-correlated transport properties are afterwards exploited in detail.