Two-impurity Kondo effect in double-quantum-dot systems: Effect of interdot kinetic exchange coupling

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-dotlead. 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.

Quantum phase transition and underscreened Kondo effect in electron transport through parallel double quantum dots

“…It is noticed that the transmission probability is proportional to the DOS for the bonding state, therefore a Kondo peak around the Fermi energy is observed in its DOS. Some new features are also manifested in DOS for this system, one can see that the DOS for the antibonding state has two side peaks nearby the Fermi energy , which can be understood as a result of the effective spin-exchange interaction between the electrons in DQDs by tunneling through the leads, and this feature cannot be found in DQDs in serial configuration [18]. As the interdot coupling t c is large than some critical value(see Fig.…”

“…The NRG method have already been applied to investigate a lot of problems in the electron transport through QD systems. For instance, DQDs connected in serial [18], the quantum phase transition in multilevel QD [19], Kondo effect in coupled DQDs with RKKY interaction in external magnetic field [20], the side coupled DQD system [21,22] and quantum phase transitions in parallel quantum QDs [23] etc. However, in our opinion the consequences of the interplay of Fano resonance and the Kondo effect on electron conductance through DQDs in parallel still haven't been well elucidated.…”

Swapping Kondo resonances in coupled double quantum dots

“…The Kondo effect for even number electrons on a single multilevel dot and possible phase transitions between singlet and triplet states have been considered for both "vertical" [5] and "lateral" [6,7,8,9] configurations. For the coupled DQD with degenerate energy levels, the Kondo behavior and the ISS interplay and strongly compete, as seen in the bulk two-impurity Kondo problem,[10] and a question arises whether there exists a spin entangled state composed of the coherent Kondo resonances.[11] Previous experimental and theoretical studies have mainly focused on the serial-coupled DQD [12,13,14,15,16,17,18,19], except for Ref. 9, 19.…”

“…For the coupled DQD with degenerate energy levels, the Kondo behavior and the ISS interplay and strongly compete, as seen in the bulk two-impurity Kondo problem, [10] and a question arises whether there exists a spin entangled state composed of the coherent Kondo resonances. [11] Previous experimental and theoretical studies have mainly focused on the serial-coupled DQD [12,13,14,15,16,17,18,19], except for Ref. 9,19.…”

“…[11] Previous experimental and theoretical studies have mainly focused on the serial-coupled DQD [12,13,14,15,16,17,18,19], except for Ref. 9, 19.…”