  We systematically investigate electron transport through double quantum dots
with particular emphasis on interference induced via multiple paths of electron
propagation. By means of the slave-boson mean-field approximation, we calculate
the conductance, the local density of states, the transmission probability in
the Kondo regime at zero temperature. It is clarified how the Kondo-assisted
transport changes its properties when the system is continuously changed among
the serial, parallel and T-shaped double dots. The obtained results for the
conductance are explained in terms of the Kondo resonances influenced by
interference effects. We also discuss the impacts due to the spin-polarization
of ferromagnetic leads.
