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標題: | 單層外延石墨烯於碳化矽基板與二維電子系統之電傳輸特性 Electronic Transport Properties in Monolayer Epitaxial Graphene on SiC and Two-dimensional GaAs/AlGaAs Heterostructures |
作者: | Chieh-Wen Liu 劉玠汶 |
指導教授: | 梁啟德 |
關鍵字: | 石墨烯,二維材料,載子濃度,量子相變,量子霍爾效應, epitaxial graphene,2D materials,carrier density,quantum phase transition,quantum Hall effect, |
出版年 : | 2017 |
學位: | 博士 |
摘要: | 許多新穎的量子物理現象可以於二維材料中觀測到。此篇論文探討在低溫及外加磁場下碳化矽上成長之單層外延石墨烯及二維砷化鎵電子系統之傳輸特性。實驗成果分為三部分。
在第一個主題中我將探討在低溫下電子-電子交互作用於單層外延石墨烯的影響以及根據古典霍爾效應和Shubnikov-de Haas效應研究載子濃度對溫度之相依性。這項研究針對載子濃度之溫度相依性提供了重要的概念,且此結果不只限制於石墨烯上也可應用於其他二維系統中。 在接下來的兩個主題,利用重整化群流的分析,其概念為藉由改變樣品之溫度等效於實際樣品大小,並結合模對稱群來理解二維電子系統中之整數量子霍爾效應及量子相變。在探討砷化鎵/砷化鋁鎵異質接面這章節裡,在低磁場不同藍道能級混成影響下,樣品仍然符合尺度推移的特性及半圓律,有別於高場中此藍道能級之混成會破破壞半圓律。重整化群流中之行為與普遍尺度推移之間的對應關係也會於此章節中討論。 最後一個實驗章節利用重整化群流探討在強無序單層外延石墨烯中之絕緣態行為。儘管在所有磁場量測下樣品一直處於絕緣態,數據結果卻顯示似量子霍爾效應的特性,並且在重整化群流的分析中觀測到稀有及獨特的流向,而此現象顯示定溫相變。 關鍵字:石墨烯、二維材料、載子濃度、量子相變、量子霍爾效應。 Two-dimensional (2D) materials provide an ideal platform for probing rich physical phenomena at the quantum level. This dissertation focuses on low-temperature magneto-transport measurements of monolayer epitaxial graphene grown on SiC and the GaAs-based 2D electron system. The experimental results include three topics. In the first study, I show how electron-electron interactions play a role in epitaxial graphene at low temperatures (T) and study the T dependence of carrier density based on the classical Hall effect and Shubnikov-de Haas measurements. This work points to an important concept regarding determination of the T dependence of the carrier density in not only graphene but also in the field of other 2D materials. For the next two parts, I investigate renormalization group (RG) flow, where by changing the measurement temperature so as to vary the effective size of a sample, as well as the modular symmetry group for understanding the quantum Hall effect and quantum phase transition of 2D electron systems. In the GaAs/AlGaAs heterostructure studied in this chapter, at low magnetic fields (B) in the insulator-quantum Hall transition resulting from Landau-level mixing, the scaling behavior and semicircle law are observed while such mixing destroys the semicircle law in the high-B regime. The correspondence between RG flow and the universal scaling function is also discussed. In the last part, the insulating behavior in strongly disordered monolayer epitaxial graphene based on RG flow is studied. Quantum Hall-like characteristics are observed even when an insulating state persists at all fields studied. The results show an unusual feature in RG flow and suggest a fixed-temperature phase transition corresponding to such feature. Keyword: epitaxial graphene, 2D materials, carrier density, quantum phase transition, quantum Hall effect. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/59248 |
DOI: | 10.6342/NTU201701347 |
全文授權: | 有償授權 |
顯示於系所單位: | 應用物理研究所 |
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