二維電子系統之量子傳輸和相圖特徵研究

Abstract

本篇論文在探討有關量子傳輸在極低溫的二維電子氣系統的特性和應用。主要分為四個實驗相關的章節。第一個部份，從基礎的物理性質如絕緣態，量子霍爾態，和磁阻振盪開始討論，並更進一步討論量子相變化的一些相關物理性質。其中決定此相變化的一個很重要的決定因素可能來至低場郎道能階的混成有關。第二個部份，更進一步使用相圖來探討改變塞曼效應對量子相變化的影響。第三個部份，探討有關電子屏蔽效應所導致非單調性的磁阻變化來由。第四部份，研究有關電子熱效應的影響和可能的應用。

量子霍爾效應是非常出名的量子傳輸效應的代表。其基本理論可以運用單一電子的侷限化模型來描述。但隨著在更多量子傳輸現象的產生。平均場論和類(準)載子系統在局部作用的模型幫助我們更加瞭解量子傳輸現象。像是直接量子霍爾態相變化可能就可以利用此相關理論來加以表述。而有關量子霍爾態的分離轉換點更可以透過此相關理論來証實。而電子-電子間的作用力也在量子傳輸作用中扮演一個很重要的角色。而電子熱效應能直接改變局部載子分佈的情形。這些都有助於我們對於量子傳輸的更一步認識和瞭解。對於發展量子傳輸裝置有很大的幫助。

This dissertation describes low-temperature transport measurements in two-dimensional electron gas systems. There are four research parts for different experiments. The first concerns the basic properties of two-dimensional electron gas systems, such as insulator, semiclassical oscillations and quantum Hall liquids at low magnetic fields. The second is a study of the renormalization group flow diagram through varying spin-splitting to delve into new quantum transport theories. The third discusses the non-monotonic magneto-resistivity due to Friedel’s oscillations. This is an important quantum transport property due to high electron concentration and strong electron-electron interactions. The fourth describes how electron heating can be a very powerful tool to study semiconductor devices. The quantum Hall effect is the most famous example in two-dimensional quantum transports. The concept of one-electron localization in the presence of a short-range disorder gives a good physics picture for understanding the phenomenon. All electron states in the broadened Landau level are localized except for electron with energy in the extended state. During the recent years, in the framework of a mean-field approximation, the concept of quasi-particles provides a more powerful tool for explaining more quantum transport properties. For example, the new boundary of global phase diagram due to low fields Landau level mixing may provide a way to explain direct insulator quantum Hall transition. The Separatrix of temperature driven flow lines may be caused by locally distribution of quasi-particles. The electron interaction causes non-monotonic magneto-resistivity due to Friedel’s oscillation by double back scattering of electrons. Electron heating may cause the non-uniform distribution of quasi-particles.