Quantum plasmons in graphene nanoribbons

Kåre Obel Wedel*

*Corresponding author for this work

Research output: Book/ReportPh.D. thesisResearch

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Abstract

In this thesis, the plasmons of graphene nanoribbons are studied in detail using quantum mechanical tight-binding calculations combined with linear response in the random phase approximation. Plasmonics is a highly active research area that shows promise in a broad range of technological applications. One of the main interests stems from the ability of the plasmons to confine light below the diffraction limit. Technological advances in nanofabrication–making structures on the nanoscale – and in the synthesis of two-dimensional materials have enabled the fabrication of a vast range of experimental structures. To understand the plasmons at these tiny length scales, modeling of quantum mechanical effects has become increasingly important. For the two high-symmetry ribbon geometries – the armchair ribbon and the zigzag ribbon – the results presented are interpreted using insight from the Dirac model, which gives analytical expressions for the band structures. On the electron-structure level, comparisons between the Dirac model, the tight-binding method, and the even more detailed Density Functional Theory (DFT), are made, illustrating the value of analytical models for understanding numerical results. The plasmon calculations on narrow ribbons show strong dependence on the atomic configuration at the ribbon edges, showing the importance of an atomistic modeling approach. Scale invariant plasmon energies are expected from the Dirac model, and are shown to emerge from the tight-binding calculations when the modeled ribbons are made wider and wider. Treating the higher-order plasmons as standing waves, a so-called Fabry-Pérot model, we calculate non-trivial reflection phases and effective width corrections for the two ribbon types. Furthermore, we find prominent short-range oscillations of the induced charges of the plasmons. An effect that can be explained with our analysis of the wave functions.
Original languageEnglish
Place of PublicationKgs. Lyngby
PublisherTechnical University of Denmark
Number of pages118
Publication statusPublished - 2018

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