Imperial College London

2019 TYC Student Day prizes

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TSM students Lara Roman Castellanos and Emanuele Galiffi have both won prizes at the TYC Student Day which took place on 15th February at Imperial.

Lara Roman Castellanos (Cohort 7) was awarded 'Best Talk 2019' for her talk entitled "Hot carrier generation from single plasmons in metallic nanoparticles".

An abstract is below:

When light impinges on a metallic nanoparticle localised surface plasmons can be excited. These are the result of the collective behaviour of conduction electrons that oscillate coupled to an electromagnetic field. The energetic electrons generated after the decay of the plasmon are of great interest due to its potential applicability in diverse nanoplasmonic devices. Most of the models available in the literature treat the plasmon as a classical dipole field induced by the charge oscillation on the surface of the nanostructrure. We propose a quantum-mechanical model where the optical properties of the nanoparticle are calculated using linear response density functional theory. In this model, the plasmon is one of the excited states found and arises from the electron-electron interactions in the metal, without requiring the addition of a classical dipole field. After the excitation, the plasmon decays producing energetic electrons. In our model, the treatment of the plasmon as a boson allows us to derive an expression for the coupling matrix between the collective excitation and the single electrons in the system. Therefore, the hot carriers distribution can be calculated for the plasmon state for different sizes and materials. We also study the decay of non-plasmonic excitations, such as electron-hole pairs, and find that they can result in similar hot carrier generation rates as plasmonic excitations
Our approach paves the way to describe hot carrier generation in the quantum plasmonic regime with potential application to quantum-controlled devices, including single-photon sources, transistors and ultra-compact circuitry at the nanoscale.

Emanuele Galiffi (Cohort 8) was awarded the prize for 'Best Poster 2019' for his poster entitled "Singular Graphene Metasurfaces".

An abstract is below:

Mathematical singularities are an effective way of describing multi-scale physics. In this work we use singular conformal maps to analytically design and characterise subwavelength metallic structures, which are able to harvest incoming electromagnetic radiation over enormous bandwidths by efficiently exciting surface waves. An example of these structured surfaces is an inhomogeneous graphene sheet, whose Fermi level periodically approaches the charge neutrality point. By exploiting this phenomenon, we design a dynamically tunable, extremely broadband THz absorber with a single layer of graphene. Furthermore, this concept can be extended to any polaritonic system which enables nano-structuring, such as hexagonal boron nitride within its mid-infrared reststrahlen bands. By deploying the elegant analytical framework of transformation optics, we develop an accurate description of the optical response of these surfaces, which allows us to highlight their connection to the concept of compacted dimensions in string theories, and illuminate the multi-scale nature of singular metasurfaces. 

Many congratulations to both Lara and Emanuele!

Reporter

Naho Ollason

Naho Ollason
National Heart & Lung Institute