Coupled Quantum Dots in the Kondo regime: interference and filtering effects.

Double quantum-dot systems (DQDs) provide a vast array of possibilities for both theoretical and experimental investigations of the Kondo regime. In this work, we propose DQDs as a possible experimental realization of a Kondo impurity coupled to an effective structured (non-constant) density of states (DoS). We consider a DQD in parallel configuration coupled to metallic leads. By changing the lead-dot and dot-dot couplings, the effective hybridization function for an individual dot displays sharp resonances and/or pseudogaps, allowing for an experimental probe into the transition between both regimes. Using numerical renormalization group methods, we calculate the dot's spectral function in different regimes. For a dot weakly coupled to the leads and strongly coupled to the second dot, the effective DoS has a sharp resonance with width $\Delta$ and the spectral density shows a splitting in the Kondo resonance for $T_K>\Delta$, although the Kondo singlet is \textit{preserved}. Furthermore, for small inter-dot coupling, second order dot-dot interactions through the conduction electrons lead to the formation of a pseudo-gap. The spectral density goes to zero as a power-law $|\epsilon-\epsilon_F|^2$ and the Kondo screening is suppressed. Supported by NFS-NIRT.