Speaker: Emanuele Galiffi, PhD candidate, Imperial College London
Title: Metasurfaces through space and time: from hidden dimensions to nonreciprocal amplification
Abstract: Blending together ideas from condensed matter physics and electrical engineering, the field of metamaterials has risen into a dynamical, highly multidisciplinary concept, with the goal of exploring the ultimate limits of wave control. In this talk I will present two different research directions for metasurfaces exploiting both space and time as potential degrees of freedom.
First, I will discuss a curious link between “singular“ metasurfaces, i.e. surfaces which feature sharp points, and the concept of hidden dimensions in string theories, demonstrating, with the aid of the analytical tool of transformation optics, that this concept underpins any optical structure with a broadband resonant spectrum. [1-4] I will then give an example of how transformation optics can be used to harness symmetry for dispersion engineering, proposing a strategy for realizing flat bands in a plasmonic system, enabling the localization of surface plasmon polaritons. 
I will then move on to demonstrate how the inclusion of even slow temporal modulations in a metasurface can yield extreme nonreciprocal effects, such as broadband one-way amplification. I will discuss the relevant physical mechanisms, and propose a graphene implementation.  Finally, I will show how doubly space-time modulated metamaterials are able to achieve nonreciprocity in the long-wavelength limit, and how this fact highlights the presence of a Fresnel drag in a medium which is at rest.
Bio: Emanuele Galiffi is a final-year PhD candidate in theoretical plasmonics and metamaterials within the group of Prof. Sir John Pendry at Imperial College London. He completed his Bachelor and Master’s studies in Physics at Imperial College and the University of Heidelberg, and, since 2016, is a graduate student within the EPSRC Centre for Doctoral Training on Theory and Simulation of Materials at Imperial College. His main research interests are transformation optics, plasmonics and time-varying metamaterials.