Three-Terminal Energy Harvester with Coupled Quantum Dots

Abstract: Rectification of thermal fluctuations in mesoscopic conductors is the key idea of today's attempts to build nanoscale thermoelectric energy harvesters in order to convert heat into a useful electric power. So far, most concepts make use of the Seebeck effect in a two-terminal geometry where heat and charge are both carried by the same particles. Here, we experimentally demonstrate the working principle of a new kind of energy harvester, proposed recently using two capacitively coupled quantum dots. We show that due to its novel three-terminal design which spatially separates the heat reservoir from the conductor circuit, the directions of charge and heat flow become decoupled in our device. This enables us to manipulate the direction of the generated charge current by means of external gate voltages while leaving the direction of heat flow unaffected. Our results pave the way for a new generation of multi-terminal, highly efficient nanoscale heat engines.

• The paper demonstrates a three-terminal energy harvester that decouples heat and charge transport using coupled quantum dots.
• The experimental setup employs a GaAs/AlGaAs structure with adjustable gate voltages to achieve asymmetric tunneling, generating a 0.6 pA charge current.
• The rate equation model validates the empirical findings, highlighting significant advances in nanoscale thermoelectric efficiency.

Three-Terminal Energy Harvester with Coupled Quantum Dots

The paper discusses the development and experimental realization of a three-terminal energy harvester utilizing two coupled quantum dots (QDs) to manipulate and harness thermal energy at nanoscale dimensions. This research presents a novel approach to thermoelectric energy conversion by introducing a design that spatially separates the heat reservoir from the conduction path, thereby allowing independent control of heat and charge flows.

Overview of the Device and Mechanism

Traditionally, thermoelectric devices have relied on the two-terminal Seebeck effect, where electronic reservoirs at different temperatures result in a heat flow that accompanies a charge current. However, this approach inherently couples heat and charge transport within the same conduits, imposing critical limitations on the thermal and electrical efficiency of the system. The present study circumvents this issue by employing a three-terminal geometry: one terminal functions as a heat reservoir, while the remaining terminals form the electrical conductor.

The harvester's core innovation lies in coupled QDs, each connected to separate reservoirs and interacting through capacitive coupling without particle exchange. This configuration enables decoupling of the thermal and electrical pathways. The system operates through a series of quasiparticle tunneling-induced occupancies across quantum dots, where energy is transferred capacitively, allowing charge flow between lower temperature conductor terminals—without necessitating direct heat flow.

Experimental Implementation and Results

The experimental setup features a device fabricated on a GaAs/AlGaAs two-dimensional electron gas (2DEG) structure with top-gate electrodes defining the QDs. The crucial element for this energy harvester is gaining control over the tunneling rates of the QDs to manipulate asymmetry. By adjusting gate voltages, the researchers successfully achieved asymmetric tunneling rates necessary for directed current generation—a key requirement to initiate energy conversion.

Significant Numerical and Theoretical Results

Quantitative evaluation revealed a charge current of approximately 0.6 pA between the QDs, maintainable even with reversed voltage biases. Such results illustrate the influence of tunneling rate asymmetries on current generation directionality, corroborated by calculation models based on experimentally derived parameters. Moreover, the paper provides rate equation approach calculations to substantiate empirical observations, ensuring that the experimentally observed currents align with theoretical predictions of energy conversion efficacy.

Implications and Future Directions

This study illustrates the potential of using capacitive coupling in nanoscale thermoelectric devices to decouple charge and heat transport, allowing for highly efficient energy conversion processes. Furthermore, the ability to modulate the direction of thermally generated current by adjusting tunnel barrier asymmetries presents a substantial advancement in thermoelectric technology.

The novel architecture and experimental validation of such multi-terminal devices portend a new generation of thermoelectric applications, particularly in environments where device miniaturization and energy efficiency are paramount. Optimizations in design, such as improved tunneling asymmetries and larger achievable temperature differentials, could enhance device performance and approach theoretical efficiency limits, such as the Carnot efficiency, paving the way for further research and development in nanoscale energy harvesting technologies.