  Electron transport through parallel double quantum dot system with interdot
tunneling and strong on-site Coulomb interaction is studied in the Kondo regime
by using the finite-$U$ slave boson technique. For a system of quantum dots
with degenerate energy levels, the linear conductance reaches the unitary limit
($2e^2/h$) due to the Kondo effect at low temperature when the interdot
tunneling is absent. As the interdot tunneling amplitude increases, the
conductance decreases in the singly occupied regime and a conductance plateau
structure appears. In the crossover to the doubly occupied regime, the
conductance increases to reach the maximum value of $G=2e^2/h$. For parallel
double dots with different energy levels, we show that the interference effect
plays an important role in the electron transport. The linear conductance is
shown to have an asymmetric line shape of the Fano resonance as a function of
gate voltage.
