The Kondo effect in coupled quantum dots is investigated from the viewpoint of transmission spectroscopy using the slave-boson formalism of the Anderson model. The antiferromagnetic spin-spin coupling J between the dots is taken into account. Conductance G through the dots connected in a series is characterized by the competition between the dot-dot tunneling coupling V C and the level broadening ⌬ in the dots ͑dot-lead coupling͒. When V C /⌬Ͻ1, the Kondo resonance is formed between each dot and lead, which is replaced by a spin-singlet state in the dots at low gate voltages. The gate voltage dependence of G has a sharp peak of 2e 2 /h in height in the crossover region between the Kondo and spin-singlet states. The sharp peak of G survives when the energy levels are different between the dots. When V C /⌬Ͼ1, the ''molecular levels'' between the Kondo resonant states appear; the Kondo resonant peaks are located below and above the Fermi level in the leads at low gate voltages. The gate voltage dependence of G has a broad peak, which is robust against J. The broad peak splits into two peaks when the energy levels are different, reflecting the formation of the asymmetric molecular levels between the Kondo resonant states.

No abstract

We investigate adiabatic pumping through a quantum dot with a single level in the mixed-valence and Kondo regimes using the slave boson mean field approximation. The pumped current is driven by a gauge potential due to time-dependent tunneling barriers as well as by the modulation of the Friedel phase. The sign of the former contribution depends on the strength of the Coulomb interaction. Under finite magnetic fields, the separation of the spin and charge currents peculiar to the Kondo effect occurs.

We investigate an adiabatic spin pumping through a quantum dot with a single orbital energy level under the Zeeman effect. Electron pumping is produced by two periodic time dependent parameters, a magnetic field and a difference of the dot-lead coupling between the left and right barriers of the dot. The maximum charge transfer per cycle is found to be $e$, the unit charge in the absence of a localized moment in the dot. Pumped charge and spin are different, and spin pumping is possible without charge pumping in a certain situation. They are tunable by changing the minimum and maximum value of the magnetic field.Comment: RevTeX4, 5 pages, 3 figure