EPSRC CDT in Metamaterials (PhD Studentship): Photosynthetic Metamaterials

University of Exeter - Departments of Physics and Engineering

Joint supervisors: Prof Bill Barnes, Dr Isaac Luxmoore, Dr Philip Thomas

External supervisor: Prof. Graham Leggett, University of Sheffield

Photosynthesis harnesses the collective action of many pigment (dye) molecules working in concert. Indeed, speculation has been rife in recent years that quantum coherence may be important in photosynthesis. Whether this is true or not is still a controversial topic, but the fascinating optical and excitonic properties of these molecules and molecular complexes provide other important opportunities. In this project an entirely new use for photosynthetic molecules is proposed – using them to provide nanoscale confinement, enhancement and guiding of light. The absorption of some photosynthetic light harvesting complexes (similar to those found in spinach) is sufficiently strong that the associated permittivity goes negative. This negative permittivity gives materials made from such molecules a plasmonic character (J. Opt, 18, 015001 (2016))

Although these ideas are now becoming established (Barnes and others, 2014-2017, see e.g. Nano Letters, 14, 2339 (2014)) NO ONE has yet managed to make artificial nanostructures from these molecules. It is only by introducing nanostructure that the full power of such materials to control light will be achieved – just as has been the case for metals and plasmonics (Nature, 424, 824 (2003)).

FURTHER, combining these nano-structured materials with ideas from metamaterials, entirely unexplored realms will be opened. In particular, nanostructured photosynthetic molecular elements will become a new class of meta-atoms, thereby enabling novel molecular metamaterials to be investigated. Prospects include greatly enhanced transport of excitons in synthetic light-harvesting structures (PRL, 114, 196402 (2015)), potentially important for future clean fuel technologies.
The main thrust of the project will be to fabricate nanostructured molecular assemblies from photosynthetic molecular complexes, characterise their optical properties (absorption, residual fluorescence, permittivity, field confinement) and then exploit them to make molecular metamaterial structures to greatly (many orders of magnitude) enhance exciton conductance with artificial photosynthesis in mind. As an example of the metamaterial-type structure considered, sub-wavelength arrays of photosynthetic ‘nanoparticles’, i.e. meta-atoms will be investigated. Electromagnetic interactions between these meta-atoms are expected to provide the coherence needed for extended exciton transport (Nano Letters – in-press).

Carrying out this project within the CDT is ideal because of the many different aspects within the CDT that will overlap with the proposed project, these include: microwave metamaterials, quantum metamaterials, together with a range of approaches to explore theoretically/numerically the problems involved (wave physics, finite-element modelling). The cohort approach to training will also benefit the student to quickly develop a professional approach, directly relevant for the collaborative nature of this project (it will involve research visits to Sheffield and may involve working in the US for short periods).

This studentship is part of the Centre of Doctoral Training in Metamaterials. Please see all fully funded opportunities.

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