Linear Conductance through Parallel Quantum Dot Dimer below the Kondo Temperature

The conductance through two quantum dots connected in a series is examined below the Kondo temperature as a function of the gate voltage attached to the dots. The ratio of the tunneling coupling between two dots to the level broadening characterizes the transport properties. When the ratio is less than unity, each dot accommodates one electron and forms the Kondo resonant state with an external lead at a sufficiently low gate voltage. In the valence fluctuating regime, the number of electrons in the dots decreases from two to zero whereas the conductance is suppressed. The corresponding range of the gale voltage is nearly the level broadening. When the ratio is larger than unity, the Kondo resonances arc split into the bonding and antibonding peaks. The valence fluctuating regime is extended over the tunneling coupling between the two dots.