Electronic Transport Properties in Monolayer Epitaxial Graphene on SiC and Two-dimensional GaAs/AlGaAs Heterostructures

• Main Authors: Chieh-Wen Liu, 劉玠汶
• Other Authors: 梁啟德
• Format: Others
• Language: en_US
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/j3mcrn

博士 === 國立臺灣大學 === 應用物理研究所 === 105 === 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.