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

TL;DR

This study investigates how increasing interdot coupling in a double quantum dot system affects charge transport, revealing a transition from localized states to molecular-like behavior and the impact of temperature on coherence.

Contribution

It provides experimental insights into the crossover from weak to strong interdot tunneling and highlights the multi-level effects and localization phenomena in double quantum dots.

Findings

Crossover from weak to strong interdot coupling observed in charge stability diagrams.

Double quantum dot states are mainly localized except in intermediate coupling.

Temperature increases lead to loss of coherence in molecular states.

Abstract

We report low-temperature transport measurements through a double quantum dot device in a configuration 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 in the charge stability diagrams that present a complex pattern with mergings and apparent crossings of Coulomb blockade peaks. While the weak coupling regime can be understood by considering a single level on each dot, in the intermediate and strong coupling regimes, the multi-level nature of the quantum dots needs to be taken into account. Surprisingly, both in the strong and weak coupling regimes, the double quantum dot states are mainly localized on each dot for most values of the parameters. Only in an intermediate coupling regime the device presents a single dot-like molecular behavior 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 molecular states is observed.