The role of the indirect tunneling processes and asymmetry in couplings in orbital Kondo transport through double quantum dots

A system of two quantum dots attached to external electrodes is considered theoretically in the orbital Kondo regime. In general, the double dot system is coupled via both Coulomb interaction and direct hopping. Moreover, the indirect hopping processes between the dots (through the leads) are also taken into account. To investigate the system's electronic properties we apply the slave-boson mean field (SBMF) technique. With the help of the SBMF approach the local density of states for both dots and the transmission (as well as linear and differential conductance) is calculated. We show that Dicke- and Fano-like line shapes may emerge in the transport characteristics of the double dot system. Moreover, we observed that these modified Kondo resonances are very susceptible to the change of the indirect coupling's strength. We have also shown that the Kondo temperature becomes suppressed with increasing asymmetry in the dot-lead couplings when there is no indirect coupling. Moreover, when the indirect coupling is turned on the Kondo temperature becomes suppressed. By allowing a relative sign of the nondiagonal elements of the coupling matrix with left and right electrodes, we extend our investigations to become more generic. Finally, we have also included the level renormalization effects due to indirect tunneling, which are mostly neglected. (paper)