High magnetic field effects in low-dimensional carbon nanostructures

Thesis

This thesis describes studies of graphene, single walled carbon nanotubes (SWNTs) and InSb. Optical and electronic measurements probe the effects of high magnetic fields on these low-dimensional systems.

Chapter 1 introduces a theoretical description and background behind the materials and physical phenomena studied in this work. The structure and unique properties of carbon nano-materials are described. The experimental methods used in this thesis are described in Chapter 2.

Chapter 3 describes magnetotransport measurements on InSb/AlInSb heterostructures revealing that the large energy gaps, and extremely high mobility, associated with this system leads to exceptionally well defined quantum Hall plateaux for both even (Landau level) and odd (spin-split) filling factors. Even higher cyclotron energy gaps are expected in graphene. Chapter 4 reveals that due to a combination of large cyclotron energy gaps and fast electron-phonon energy loss rates, the quantum Hall effect (QHE) in graphene can be observed to unprecedented current densities (43 A/m) and temperatures (> 45 K). The behaviour of epitaxial graphene grown on silicon carbide in the quantum Hall regime is shown to be characterised by a strongly magnetic field dependent carrier density due to charge transfer from surface donor states in the substrate.

Chapter 5 shows that polymer wrapping of SWNTs can achieve high quality purified samples. Individual SWNTs were probed using micro-photoluminescence measurements in magnetic fields up to 30 T. The combination of high magnetic fields and high spectral and spatial resolution allowed a detailed study of exciton fine structure. High intensity laser irradiation is shown to induce bound excitons in pristine tubes. The optical properties of a number of tubes are dominated by defect sites which may be imaged along the tube using the magnetic brightening of dark excitons associated with such defects.

Authors: Alexander-Webber, J; Jack Alexander-Webber

• Publication date: 2013
• DOI: 10.5287/ora-jv0ezeeky
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: Oxford University, UK
• Language: English
• Keywords: Carbon nanotubes; Physics; Nanotechnology; Graphene
• Subjects: Condensed Matter Physics