Investigation On The Performance Characteristics Of Coulomb-Coupled Quantum-Dot Thermoelectric And Thermal Management Devices

With the development of nanoscience and quantum technology,physical processes at the nanoscale have brought new opportunities and challenges for today’s technological revolutions and also provided rich soil for the development of emerging disciplines.Quantum thermodynamics is an emerging discipline that focuses on the thermodynamic performances in quantum systems at the nanoscale.One of the current research hot-pots is the transport and conversion of heat and electricity at the nanoscale.It is of great significance for the development and application of basic physics.Based on Coulomb-coupled quantum dots,this thesis studies the thermo-electric conversion performance and the thermal management and regulation of quantum systems.This thesis mainly consists of two parts.The first part includes chapters 2-4 and mainly focuses on the thermo-electric conversion performance at the nanoscale.In this part,a three-thermal quantum dot thermoelectric device based on the Coulomb-coupled model of two quantum dots is established.In this three-terminal structure,it can effectively decouple the heat flow and the charge current,and realize the effective separation of the hot and cold reservoirs.The heat exchange between the hot and cold reservoirs can only be achieved by the Coulomb interaction between the two quantum dots.The three-thermal quantum dot thermoelectric device can directly convert a part of heat from the hot reservoir to electricity based on the Seebeck effect and also work as a solid-state heat pump or refrigerator to pump heat from the cold reservoir to the hot reservoir by electricity based on the Peltier effect.It is further proposed that the three-terminal quantum dot heat engine and refrigerator have,respectively,two different working modes,that is,different systemic parameter configurations can meet different work requirements.The thermodynamic performances and optimum characteristics of the heat engine and refrigerator are investigated.The optimal ranges of the heat engine and refrigerator in two differentconfigurations are determined.The influence of asymmetric energy-dependent tunneling on the thermodynamic properties and optimization of thermoelectric devices are systematically analyzed.The thermodynamic characteristics and the optimized performance at the maximum power output of the heat engine in two different configurations are compared.The results obtained show that under ideal conditions,both the heat engine and refrigerator can work reversibly in two different configurations and can achieve the Carnot efficiency.In addition,asymmetric energy-dependent tunneling is a necessary condition for the realization of a three-terminal quantum dot heat engine or refrigerator.It is also a key factor that causes irreversible losses in the system.Therefore,asymmetric energy-dependent tunneling affects profoundly the systemic electron and energy transport and the performance of the thermoelectric device.This part as a research focus of quantum thermodynamics is of important theoretical significance for the deep understanding of the thermodynamic performances in quantum systems and also provides important theoretical guidance for the development of new types of nano-thermoelectric devices and their practical applications.The second part includes chapters 5 and 6 and mainly focuses on the thermal management at the nanoscale.Heat flows can be manipulated by designing a quantum dot system consisting of three Coulomb-coupled quantum dots connected to respective reservoirs.In this structure the electron transport between the quantum dots is forbidden but the heat transport is allowed by the Coulomb interaction to transmit heat between the reservoirs with a temperature difference.It is shown that such a system is capable of performing thermal management operations,such as heat flow swap,thermal switch,and heat path selector.Two important components,the thermal diode and the thermal transistor,are established.The thermal diode is a device that is analogous to an electrical diode and allows heat passing in one direction depending on the applied temperature bias and is blocked in the opposite direction.The thermal diode can be implemented separately in two different paths with significant thermal rectification.The three-terminal quantum dot system has abnormal heat transport characteristics,showing the phenomenon of negative differential thermal resistance.This is the main ingredient for the thermal transistor effect.Therefore,a quantum-dot thermal transistor is analogous to an electronic transistor consisting of three terminals:the base,the collector,and the emitter.The heat flows through the collector and emitter can be controlled by the temperature of the base.It is found that a small change in the base heat flow can induce a larger heat flow change in the collector and emitter.Such a thermal transistor is able to amplify a small heat signal that is injected into the base.The huge amplification factor can be obtained by optimizing the Coulomb interaction between the collector and the emitter or the energy-dependent tunneling rate at the base.The quantum dot thermal management device proposed in this part provides a feasible solution for engineering heat transport at the nanoscale and has potential applications in low-temperature solid-state thermal circuits.