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Quantum effects in the optical response of metallic nanoantennas

AuthorsAizpurua, Javier
Issue Date2015
CitationCECAM-HQ-EPFL (2015)
AbstractThe optical response of nanometric-sized metallic particles is well described within the framework of Electrodynamics. Linear local dielectric theory within Maxwell¿s equations provides a very adequate description of the evolution of electric and magnetic fields that adapt to the boundaries of a particular structure, providing information about the absorption and scattering of light by it. In metallic nanoparticles, the optical response is mainly governed by the excitation of localized surface plasmons, the collective oscillation of the surface charge density at the particle following the electromagnetic modes imposed by the geometrical boundary conditions. As the dimensions of nanoparticles reach a few nanometers or even Ångstroms, the quantum nature of the electrons building up the optical response becomes noticeable, and important departures of the standard local response can be identified. The description of a full quantum model to describe the optical response will be introduced within Time-Depedent Density Functional Theory (TDDFT). This fully quantum mechanical approach allows to consider (i) quantum size effects, (ii) nonlocal dynamical screening, and (iii) spill-out of the electron cloud at the boundaries. Beyond the case of single nanoparticles, gap-nanoantennas formed by strongly-coupled metallic nanoparticles also provide the capability to tune the optical response on demand. A switch between a capacitive and conductive situation within the gap modifies the plasmonic modes allowing for a variety of applications such as all-optical switching, near-field coherent control of single emitters, or probing of transport properties at optical frequencies. As metallic nanoparticles come close together at subnanometric distances, the plasmonic nanogap enters a strong nonlocal regime. For the smallest separations, electron quantum tunnelling across the gap is possible at optical frequencies modifying dramatically the optical response of the system. To account for the effect of the spill-out of the electrons at the surface of the metal as well as the coherent tunnelling that can be established across the gap, full quantum mechanical calculations of the optical response are necessary. Considering the limitations of quantum calculations to relatively small systems, I will present a method particularly suitable to include quantum effects in large realistic plasmonic systems, the quantum-corrected model (QCM). Recent experimental situations where the quantum regime in subnanometric gaps has been revealed will be described, as well as general concepts of nonlocality and nonlinearities within the quantum plasmonic response. Finally, I will present some results regarding the importance of an atomistic description of metallic nanoparticles to correctly address the near-field distribution around the particles, where we identify subnanometric localization of light thanks to the effect of crystallographic facets, edges and vertices.
DescriptionResumen del trabajo presentado al CECAM workshop on: "Computational plasmonics: an ab initio and multiscale perspective", celebrado en Lausanne (Suiza) del 2 al 4 de noviembre de 2015.
Appears in Collections:(CFM) Comunicaciones congresos
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