Doctor of Philosophy
School of Engineering Physics
Wright, Anthony, Electronic and Optical Properties of Graphene, Doctor of Philosophy thesis, School of Engineering Physics, University of Wollongong, 2010. http://ro.uow.edu.au/theses/3123
We investigate the electronic and optical properties of various one and two dimensional graphene based materials. Using the tight binding approximation, we calculate the electronic dispersions of these systems. Using Green's functions, we then evaulate the dielectric function within the random phase approximation (RPA), and the corresponding collective excitation spectrum for armchair grapheme nanoribbons. We also calculate the Kubo formula-based optical conductivity of single layer graphene, bilayer graphene, graphene nanoribbons, bilayer graphene nanoribbons, and stretched graphene. For single layer graphene within the Dirac approximation we also calculate the third order nonlinear optical conductance (a nonlinear correction to the `universal' conductivity, as well as a frequency tripling term) and finally the effect of electron-LO phonon scattering on the `universal' conductivity at various temperatures and doping levels.
There are several results of particular interest. We predict a roton-like mode in the collective excitation spectrum of non-Dirac armchair graphene nanoribbons. We also demonstrate a two order of magnitude enhancement to the optical conductivity of an entire subclass of bilayer graphene nanoribbons in the terahertz-far infrared regime. A strong nonlinear conductance of single layer graphene under moderate field strengths at room temperature is derived. Finally, stretching induced hall optical conductivity and chirality dependent anisotropy in single layer graphene under conservative stretching conditions are predicted.
We find that the optical properties of graphene based materials are remarkably robust and highly tunable, particularly within the terahertz to far-infrared regime. Furthermore, the prediction of a roton-like minimum in the collective excitation spectra of a subclass of armchair ribbons makes these particular graphene based materials part of an extremely small subclass of materials, and represents the opening of a potentially huge new field of fundamental research.
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