Electron Transport Through Coupled Quantum Dots Below the Kondo Temperature

Conductance G, through coupled quantum dots in series isinvestigated below the Kondo temperature, based on the slaveboson formalism of the Anderson model with theantiferromagnetic spin–spin coupling J. Electron transport ischaracterized by the ratio of the dot–dot tunneling couplingV_C to the level broadening in the dots (dot-lead coupling). When V_C/<1, the Kondoresonance is formed in each dot and lead and G is determinedby hopping between the two Kondo states. They are replaced bya spin-singlet state in the dots for low gate voltages. Thegate voltage dependence of G has a sharp peak of 2e²/h inheight in the crossover region between the spin-singlet andKondo states. When V_c/>1, the Kondo levelsare split below and above the Fermi level in the leads for lowgate voltages. The gate voltage dependence of G has a broadpeak, which is fairly robust against J. This broad peak isdivided into two peaks when the energy levels are differentbetween the dots.