  We investigate the Kondo effect in a quadruple quantum dot device of
coupled-double quantum dots (DQDs), which simultaneously contains intra-DQDs
and inter-DQDs coupling. A variety of novel behaviors are observed. The
differential conductance dI/dV is measured in the upper DQDs as a function of
source drain bias. It is found to exhibit multiple peaks, including a zero-bias
peak, where the number of peaks exceeds five. Alternatively, tuning the lower
DQDs yielded regions of four peaks. In addition, a Kondo-effect switcher is
demonstrated, using the lower DQDs as the controller.
