拓樸絕緣體自旋閥的自旋電流及磁阻

Abstract

本論文主旨為研究拓樸絕緣體自旋閥之自旋電流及磁阻效應．首先闡述了我的研究動機與介紹了拓樸絕緣體之歷史與發展並說明了自旋閥元件其運作原理及其中的自旋極化電流與磁阻效應之概念．接著在過程中，首先以狄拉克原理為基礎，推廣到拓樸絕緣體之漢米爾頓算符並求得其能量本徵值與波函數特徵向量，接著求得拓樸絕緣體自旋閥結構下之穿透率、電流及磁阻率並建構出拓樸絕緣體自旋閥之基礎理論模型．本論文分別評估了能隙、週期數以及電壓位障對於拓樸絕緣體自旋閥所帶來的影響，其中又以能隙的提升直接的影響到禁帶區域的大小最有效於提升磁阻率，發現最高可超過3000%。而週期數在考量到實際應用於電子元件上的大小時，適當的提升也有助於提升磁阻率。此外，適當地設計電壓位障也可以得到最佳化的磁阻率。

The main purpose of this thesis is to investigate the spin current and magnetore-sistance effect of topological insulator spin valves. First of all, I expounded my research motivation and introduced the history and development of topological insulator, and explained the operation principle of spin valves components and the related concepts of spin polarization current and magnetoresistance effect. Then in the process, firstly based on the Dirac principle, and then extended to the Hamiltonian operator of topological insulator to get its energy eigenvalue and wave function eigenvector. Then obtain the transmission, current and magnetoresistance, and construct the basic theoretical model of the topological insulator spin valves. This thesis separately investigates the influence of energy gap, numbers of cells and voltage barrier on the topological insulator spin valves. Among them, the increase of the energy gap directly affects the size of the for-bidden band region and is most effective in increasing the magnetic resistance, and it is found that the highest can exceed 3000%. When considering the size of the actual ap-plication to the electronic components, the appropriate increase the numbers of cells will increase the magnetic resistance. Moreover, the largest magnetic resistance can be achieved when the voltage barrier is properly designed.