Zero-bias conductance through side-coupled double quantum dots

Low temperature zero-bias conductance through two side-coupled quantum dots is investigated using Wilson's numerical renormalization group technique. A low-temperature phase diagram is computed. Near the particle-hole symmetric point localized electrons form a spin-singlet associated with weak conductance. For weak inter-dot coupling we find enhanced conductance due to the two-stage Kondo effect when two electrons occupy quantum dots. When quantum dots are populated with a single electron, the system enters the Kondo regime with enhanced conductance. Analytical expressions for the width of the Kondo regime and the Kondo temperature in this regime are given.