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Title: Electromagnetic field enhancement in classical and quantum plasmonics
Author: Fitzgerald, Jamie
ISNI:       0000 0004 7658 8541
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2019
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Plasmonics has ushered in an era of precise control over light using the hybrid light-matter collective oscillations of electrons in metals, it is sandwiched in-between the realms of electronics and photonics, i.e. nanometre devices operating at frequencies beyond the terahertz. It offers the promise to mirror the huge technological impact that electronics and photonics have had on all our lives, providing an interface between the two that combines the strengths of each. One of the most defining features of plasmonics is 'hot spots': regions of extreme field enhancement confined to sub-diffraction volumes. Simulations of these highly localised fields are numerically challenging and need sophisticated theory involving a firm understanding of the intricacies of the near-field. In this work, the physics of extreme field enhancement is explored by considering three exemplary systems in classical and quantum plasmonics: the cavity, the nanolens, and the nanorod. For the cavity geometry, the role of new nanophotonic materials, graphene and polar dielectrics, are explored for building a novel platform for molecular sensing in the mid-infrared. Furthermore, the role of strong-coupling between the constituent modes is analysed. For the nanolens, the limits of extreme field enhancement are explored in the quantum regime where nonlocal losses kill strong nanolensing, and in the micron regime where localised surface phonon polaritons excited in polar dielectrics lead to unprecedented field enhancements on the order of 10^4. Far superior to disappointing metallic nanolenses, which are found to offer no better performance than the simpler spherical dimer geometry. Finally, the ultimate small size limit of the nanorod is explored: the single-atom-thick atomic chain. Electronic structure methods are used to identify quantum plasmons and explore the main loss channel at these sizes: plasmon-phonon coupling. This allows ab initio calculation of field enhancements, a first in quantum plasmonics.
Supervisor: Giannini, Vincenzo ; Hess, Ortwin Sponsor: Bristol-Myers Squibb Company ; Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral