Transport through side-coupled double quantum dots: from weak to strong interdot coupling

Consejo Nacional de Investigaciones Cient´ificas y T´ecnicas (CONICET), Argentina(Dated: February 9, 2012)We report low-temperature transport measurements through a double quantum dot device in aconfiguration where one of the quantum dots is coupled directly to the source and drain electrodes,and a second (side-coupled) quantum dot interacts electrostatically and via tunneling to the first one.As the interdot coupling increases, a crossover from weak to strong interdot tunneling is observed inthe charge stability diagrams that present a complex pattern with mergings and apparent crossingsof Coulomb blockade peaks. While the weak coupling regime can be understood by considering asingle level on each dot, in the intermediate and strong coupling regimes, the multi-level nature of thequantum dots needs to be taken into account. Surprisingly, both in the strong and weak couplingregimes, the double quantum dot states are mainly localized on each dot for most values of theparameters. Only in an intermediate coupling regime the device presents a single dot-like molecularbehavior as the molecular wavefunctions weight is evenly distributed between the quantum dots.At temperatures larger than the interdot coupling energy scale, a loss of coherence of the molecularstates is observed.I. INTRODUCTION