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\nPrincipal supervisor: C. Martijn Wubs

\nCo-supervisor: N. Asger Mortensen

\nCo-supervisor: Kristian Sommer Thygesen

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\nAssociate Professor Andrei Lavrinenko (chairman) - alav@fotonik.dtu.dk

\nProfessor Thomas Garm Pedersen - tgp@mp.aau.dk

\nDr. Sigmund Kohler - sigmund.kohler@icmm.csic.es

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\nAssociate Professor Sanshui Xiao

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\nPlasmonics is a highly active research area that shows promise in a broad range of technological applications. Plasmons can be thought of as waves in a sea of electrons, and one of the main interests stems from their ability to confine light below the diffraction limit. Technological advances in nanofabrication – making structures smaller than one thousandth of the width of a human hair – and in the synthesis of two-dimensional materials have enabled the fabrication of a vast range of experimental structures. However, to understand the plasmons at these tiny length scales, modeling of quantum mechanical effects has become increasingly important. Graphene is one of the most interesting 2D materials, and in this work, the plasmons of graphene nanoribbons are examined using quantum-mechanical calculations on different levels of approximations. Linear response theory, in combination with atomistic tight-binding, yields precise numerical results, while the Dirac approximation is used to gain analytical insights. Of special interest to this work are the differences between the two high-symmetry ribbon geometries – the armchair ribbon and the zigzag ribbon – that behave vastly different when on the nanometer scale. In zigzag ribbons, the occurrence of localized, electronic edge states introduces new behaviors that are not predicted using classical models, such as a wavelength dependent reflection phase at the edge.

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