The Spin Electron Transport Of Quantum Dot System Model

With the development of emerging technology, a growing number of nanoquantum devices have been developed. And due to the transport properties of the system determine the characteristics of the device, the study of the transport properties has important theoretical significance and potential application value. Quantum spin transport in mesoscopic systems is one of the very active frontier research fields of condensed matter physics recently. It not only reveals a number of important physical intrinsic, but also showing a broad application prospects. In our work we mainly investigate spin transport properties in quantum dots systems, including the following four aspects, the detail as follows:In Chapter 1, we introduce the background and current status in mesoscopic systems, the development of quantum devices, spintronic devices and their applications, the spin-polarized transport properties in mesoscopic scale systems especially in quantum dot system. We give a brief introduction of several schemes dealing with transport issues in mesoscopic systems which people mainly employed.In Chapter 2, we introduce some basic theories which were used to investigate the transport properties in mesoscopic systems, mainly including Buttiker scattering matrix theory, Non-equilibrium green’s function method, Master equation. And we briefly describe the above basic definitions and concepts’ application in quantum dot system.In Chapter 3, In order to realize an efficient spin injection in spintronic devices, a fully spin-polarized current or a pure spin current(without an accompanying charge current) as a highly possible method has generated widespread interest. Recently,three-terminal spin devices have been widely proposed to generate the fully spin-polarized or pure spin current. Our three-terminal quantum dot system composed of a quantum dot coupled to a ferromagnetic(FM) metal lead and two nonmagnetic semiconductor(SC) leads, and the polarization current in the three-terminal quantum dot system is calculated by using the Non-equilibrium green’s function method. Consequently, we find the plateaus of fully spin-polarized current or pure spin current in one of nonmagnetic semiconductor leads by adjusting the voltage in another SC lead,and that the plateaus will not disappear in a wide range of voltage.In Chapter 4, we investigate theoretically the influence of some parametersincluding the temperature tkB, quantum dot level0? which controlled by gate voltage and other terminal voltage on the plateaus of the pure spin current and fully spin-polarized current. We found that the plateaus of the pure spin current and fully spin-polarized current in SC1 lead will be affected considerably when the parameters are varied. Due to the fluctuation of these parameters is often inevitable actually, we investigated the compensation for the influence of these parameters on the plateaus of the pure spin current. In this way, we can counteract the influence of these parameters on the plateaus of the pure spin current. Furthermore, in order to make our proposal more convincing, we also show that the devices for different device parameters and get the similar conclusionsAt last, we present a conclusion of this thesis.