Two-Impurity Kondo Effect in Double-Quantum-Dot Systems - Effect of Interdot Kinetic Exchange Coupling

TL;DR

This paper investigates the complex interplay of Kondo singlet states and interdot coupling in double-quantum-dot systems, revealing conductance peaks and quantum critical behavior through numerical renormalization group analysis.

Contribution

It provides a detailed numerical study of the two-impurity Kondo effect in double quantum dots, highlighting the effects of interdot kinetic exchange coupling.

Findings

Conductance peaks at state transition boundaries reach the unitarity limit.

Identification of a quantum critical transition affecting the energy scale of the conductance peak.

Revealing a new realization of the two-impurity Kondo problem in quantum dot systems.

Abstract

Tunneling conductance through two quantum dots, which are connected in series to left and right leads, is calculated by using the numerical renormalization group method. As the hopping between the dots increases from very small value, the following states continuously appear; (i) Kondo singlet state of each dot with its adjacent-site lead, (ii) singlet state between the local spins on the dots, and (iii) double occupancy in the bonding orbital of the two dots. The conductance shows peaks at the transition regions between these states. Especially, the peak at the boundary between (i) and (ii) has the unitarity limit value of $2e^{2}/h$ because of coherent connection through the lead-dot-dot-lead. For the strongly correlated cases, the characteristic energy scale of the coherent peak shows anomalous decrease relating to the quantum critical transition known for the two-impurity Kondo effect. The two dots systems give the new realization of the two-impurity Kondo problem.