Crossover between two different Kondo couplings in side-coupled double quantum dots

TL;DR

This paper investigates the Kondo effect in side-coupled double quantum dots, focusing on the transition between two singlet ground states as the energy level of the embedded dot varies, using numerical renormalization group analysis.

Contribution

It introduces a detailed analysis of the crossover between two Kondo screening mechanisms in double quantum dots, deriving distinct Hamiltonians for each regime.

Findings

Identification of two different Kondo screening regimes

Derivation of separate Kondo Hamiltonians for each regime

Demonstration of the crossover via numerical renormalization group

Abstract

We study the Kondo effect in side-coupled double quantum dots with particular focus on the crossover between two distinct singlet ground states, using the numerical renormalization group. The crossover occurs as the quantized energy level of the embedded dot, which is connected directly to the leads, is varied. In the parameter region where the embedded dot becomes almost empty or doubly occupied, the local moment emerging in the other dot at the side of the path for the current is screened via a superexchange process by the conduction electrons tunneling through the embedded dot. In contrast, in the other region where the embedded dot is occupied by a single electron, the local moment emerges also in the embedded dot, and forms a singlet bond with the moment in the side dot. Furthermore, we derive two different Kondo Hamiltonians for these limits carrying out the Schrieffer-Wolff transformation, and show that they describe the essential feature of the screening for each case.