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Title:Screening and the effective fine structure constant in graphene
Author(s):Gan, Yu
Director of Research:Abbamonte, Peter M.
Doctoral Committee Chair(s):Mason, Nadya
Doctoral Committee Member(s):Stone, Michael; Neubauer, Mark
Department / Program:Physics
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):dielectric screening
fine-structure constant
condensed matter physics
inelastic x-ray scattering
Abstract:This thesis discusses two main topics – the effective fine-structure constant of and dielectric screening in graphene, and a new coherent inelastic x-ray scattering technique for attosecond resolution imaging of excitations in crystalline materials. The strength of electron-electron interactions in graphene is expected to be large due to the unusual dispersion relation of graphene’s electrons and its two-dimensional nature, but evidence of strong-correlation effects and non-Fermi liquid behavior remains limited. We describe a method to probe the strength of these interactions, characterized by an effective fine-structure constant α∗(q, ω), as measured with inelastic x-ray scattering (IXS) on graphite. We show how to convert our experimentally obtained spectra, which are proportional to the imaginary part of the response function of graphite, to the full response function of graphene. We compare these results to calculated response functions in the random phase approximation (RPA) with and without interlayer hopping terms, and determine that interlayer hopping alone cannot be responsible for the observed deviations away from the RPA, due to a combination of both electron-hole interactions (excitonic effects) and additional screening from the higher energy bands. Lastly, we describe the theoretical framework for coherent inelastic x-ray scattering, a method to measure the response function for inhomogeneous media, where the off-diagonal elements of the response function are non-trivial. We use a simple model to assess the experimental feasibility of our proposed method, and show that for a perfect crystal, a full three-dimensional experimental geometry is sufficient to recover the off-diagonal response of highly inhomogeneous materials.
Issue Date:2014-12-22
Rights Information:Copyright 2014 Yu Gan
Date Available in IDEALS:2015-07-22
Date Deposited:May 2015

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