Thermal control and generation of charge currents in coupled quantum dots

Abstract

This article reviews recent thermoelectric experiments on quantum dot (QD) systems. The experiments focus on two types of inter-dot coupling: tunnel coupling and Coulomb coupling. Tunnel-coupled QDs allow particles to be exchanged between the attached reservoirs via the QD system. Hence, an applied temperature bias results in a thermovoltage. When being investigated as a function of QD energies, this leads to the thermopower stability diagram. Here, largest thermovoltage is observed in the regions of the triple points. In a QD system which exhibits only capacitive inter-dot coupling, electron transfer is suppressed. Such a device is studied in a three-terminal geometry: while one QD connects to the heat reservoir, the other one can exchange electrons with two reservoirs at a lower temperature. When the symmetry of the tunneling coefficients in the cold system is broken, the device becomes an energy harvester: thermal energy is extracted from the heat reservoir and is converted into a directed charge current between the two cold reservoirs. This review illustrates the large potential of multi-QD devices for thermoelectrics and thermal management at the nanometer-scale. In this article, the authors review the thermoelectric properties of a coupled quantum dot system which can be viewed as an artificial molecule. The first part presents the measurement of the thermopower generated by such a system located between a hot and a cold reservoir. In the second part it is discussed how coupled quantum dots can be used to extract energy from the hot reservoir and convert it into a directed current without particle exchange.