Thermoelectrics with Coulomb-coupled quantum dots

In this article we review the thermoelectric properties of three terminal devices with Coulomb-coupled quantum dots (QDs) as observed in recent experiments [1], [2]. The system we consider consists of two Coulomb-blockade QDs, one of which can exchange electrons with only a single reservoir (heat reservoir), while the other dot is tunnel coupled with two reservoirs at a lower temperature (conductor). The heat reservoir and the conductor interact only via the Coulomb coupling of the quantum dots. It has been found that two regimes have to be considered. In the first one, the heat flow between the two systems is small. In this regime, thermally driven occupation fluctuations of the hot QD modify the transport properties of the conductor system. This leads to an effect called thermal gating. Experiments have shown how this can be used to control charge flow in the conductor by means of temperature in a remote reservoir. We further substantiate the observations with model calculations, and implications for the realisation of an all-thermal transistor are discussed. In the second regime, the heat flow between the two systems is relevant. Here the system works as a nanoscale heat engine, as proposed recently (Sánchez and Büttiker [3]). We review the conceptual idea, its experimental realisation and the novel features arising in this new kind of thermoelectric device such as decoupling of heat and charge flow.