Thermoelectric Transport In Three-terminal Quantum Dot Quantum System

With the rapid development of society,the consumption of non-renewable energy is increasing,and the energy crisis is becoming more and more serious.It has become an urgent task for the pursuit of renewable energy and the secondary utilization of energy at present.An important challenge of future technology is to manufacture intelligent equipment with high energy efficiency,multi-function,and less material consumption.Thermoelectric energy conversion is a high-quality renewable energy source,and it has the advantages of no mechanical loss,no noise,long lifetime,etc.In recent years,nanotechnology and heat-work conversion have promoted the research of nano-devices,such as thermoelectric rectifier,thermal transistor.Quantum thermoelectric transport can help us to detect the transport properties of quasiparticles and elementary excitations at the micro-and nano-scales,and find materials with high thermal conductivity to create new heat dissipation devices.In this thesis,we first discuss the steady-state transport properties in various mesoscopic or nanosystems and the fundamental aspects of heat-work conversion at nanoscale and introduce the theoretical and experimental progress of quantum thermoelectric heat engines and thermoelectric devices in detail.By using the Landauer-Buttiker formula,non-equilibrium Green's function method and the non-equilibrium statistics,the transport and fluctuation properties of light-matter coupling mesoscopic systems are calculated.With the latest experimental progresses,the non-equilibrium statistical physics,open quantum systems,and quantum optics are integrated organically and mutually.1.The cooperative effects can be a useful tool in improving the energy efficiency and power of a quantum three-terminal thermoelectric heat engine.We study the energy efficiency and power of quantum three-terminal thermoelectric devices by considering the elastic tunneling through a single quantum dot.Facilitated by the three-terminal geometry,the device can simultaneously generate current in two channels while only one heat current is being utilized.The currents in these two channels can be superimposed in a destructive or coherent manner according to their signals.The coherent superposition between currents improves the efficiency and power of the heat engine.We call this coherent enhancement a cooperative effect.Moreover,this cooperative enhancement,dubbed as the thermoelectric cooperative effect,is found to be universal in three-terminal thermoelectric energy harvest.2.We establish the optimal efficiency and power theory of a three-terminal quantum heat engine with two independent output currents and one input heat current.We derive the maximal energy efficiency and output power and their trade-off for three-terminal thermoelectric engines with and without time-reversal symmetry.This formalism goes beyond the known results for conventional thermoelectric engines and shows some interesting features.A concrete example of a quantum-dot three-terminal thermoelectric engine is studied to demonstrate that for the same system,our setup can substantially enlarge the physical parameter region with high efficiency and power,when compared with previous setups with only one output electric current.Therefore,the setup with two output electric currents offers a promising pathway toward high-performance thermoelectric devices.Our theoretical framework also applies for thermoelectric heat engines with multiple output electric currents,providing a formalism for the study of maximal efficiency and power in complex thermoelectric materials and devices.3.Three-terminal quantum dot circuit quantum electrodynamic system can serve as diode and transistor.Recent breakthroughs in quantum-dot circuit-quantum-electrodynamics systems are promising both from fundamental perspectives and from the point of view of quantum photonic devices.However,understanding such setups as potential thermoelectric devices has been missing.By using the Keldysh non-equilibrium Green's function method,it is proved that the cavity coupled double quantum dot system can be used to be an excellent quantum thermoelectric diode and transistor.Based on the second-order perturbation method of precise polaron transformation,we find that the dependence of thermoelectric transport properties on the electron-photon interaction is beyond the prediction of the traditional second-order perturbation theory.We show that the quantum dot system integrated with the quantum electrodynamics structure of the superconducting cavity under the finite bias voltage has significant charge rectification and Peltier rectification effects due to the strong light-matter interaction.Due to the inelastic transport assisted by photons,we have further discovered the thermal transistor effect in the linear response regime,which has opened up a frontier field for quantum thermoelectric devices.4.Giant photon gain in large-scale quantum dot-circuit quantum electrodynamic systems.We study the photon and electron properties of the system in which the non-equilibrium microwave photon cavity is coupled to a the quantum dot system by using the Keldysh non-equilibrium Green's function method.It is shown that the single quantum-dot system can be used as the gain medium of the microwave cavity photons in the linear response regime.Through the calculations of the spectrum function,the transmission function and the phase response,we find that the electron-phonon and the electron-electron interactions can improve the photon gain.Although our focus is primarily on hybrid quantum dot circuit-quantum electrodynamics systems,our approach is adaptable to other light-matter systems where the gain medium consists of a mesoscopic structure.Finally,we make a simple summary of this thesis,and look forward to the future works briefly.