Investigation Into Regulation Of Thermoelectric Conversion Efficiency Of Quantum Rings

With the rapid development of nanoscience and the pursuit of miniaturization of electronic devices,improving the performance of electronic devices has become a goal people have been pursuing.Understanding deeply and investigating the thermoelectric conversion characteristics of nanodevices are not only conducive to people to improve the efficiency of using energy sources,but also have profound implications for the design of new quantum devices,and can further provide theoretical supports for how to convert waste heat from the environment into useful electrical energy.As a low-dimensional nanoscale device,the quantum ring itself has two special properties,namely quantum interference and continuous current,besides the special properties possessed by low-dimensional nanomaterials.When the quantum ring is exposed to the light,the time-reversal symmetry of the system will be broken.Therefore,studying deeply the thermoelectric transport properties of quantum rings and optimizing the performance of quantum ring heat engines will leads to the emergence of new physics,which can provide new guidelines for the design of new thermoelectric devices.The first chapter of this thesis provides a detailed overview on main contents of the thermoelectric effect,including the Seebeck effect,the Peltier effect,and the Tomson effect.Using the linear response theory,we have obtained four thermoelectric coefficients that characterize the relation between the thermoelectric effect and Onsager coefficients.Then we introduced the properties of quantum rings,preparation techniques,theoretical research methods,etc.Finally,we introduced the research advances on the thermoelectric effect of nano-systems and some aspects of performance optimization of thermoelectric heat engines.The second chapter mainly studied the thermoelectric effect of optically controlled quantum rings.In the third chapter,we studied the performance optimization at given power of quantum ring heat engine with broken time-reversal symmetry.With regard to the thermoelectric effect of quantum rings and performance optimization of quantum ring heat engines,the results obtained in this thesis are as follows:1.Using the transfer matrix method,we studied the thermoelectric transport properties of an optically controlled quantum ring.It was found that a large thermoelectric conversion efficiency can be obtained by adjusting parameters such as temperature,phase difference,radiation intensity,and radiation frequency.In addition,the radiated light can break the time-reversal symmetry of the system,and can in part improve the thermopower as well as the thermoelectric conversion efficiency of the thermoelectric system.2.Based on the linear response theory,we studied the performance optimization of a three-terminal quantum ring thermoelectric heat engine with broken time-reversed symmetry at given power.Two important parameters are proposed: the asymmetric parameter x and the generalized thermoelectric figure of merit y.We analyzed the relationships between the power(efficiency)gain and the system parameters of the quantum ring heat engine at given power,and obtained the universal bound of the efficiency at given power.At the same time,we find that when the asymmetry parameter x deviates from its symmetry value,the thermal engine efficiency can exceed the Curzon-Ahlborn limit in some ways,and even the greater efficiency can be obtained.And we can obtain the greater efficiency gain by reducing the asymmetry parameter.Finally,The fourth chapter gives the summaries and prospects of this thesis.