on 16-06-2023
We are inviting you to the public Ph.D. presentation session of João Câmara Serra, supervised by Mario G. Silveirinha, next June 16, 2023 – 15:00, at Room: LT2, 4th floor – Torre Norte, Instituto Superior Técnico.
Title: Electromagnetic Spacetime Crystals
Abstract:
Nowadays, the concept of photonic crystal encompasses structures that are periodic in space, time, and spacetime. In recent years, the evolution of technology has allowed us to explore time as a new degree of freedom to design metamaterials by applying temporal modulations of the system parameters. The study of time-varying structures started in 1958 with Frederic Morgenthaler. Since then, time modulations have been used to explore a wide range of phenomena and applications: temporal reflections, cloaking mechanisms, Fabry-Perot resonators, anti-reflection temporal coatings, inverse prism, temporal Brewster angles, momentum band gaps, and synthetic dimensions, among others.
These systems offer a unique opportunity to break non-reciprocity by tailoring the properties of material not only in space but also in time, e.g., with a time modulation of the material response so that the permittivity becomes a function of space and time. In particular, these spacetime modulations can implement synthetic linear motions and more exotic scenarios without having actual media moving. The standard way to break the time-reversal symmetry is by using a static magnetic field bias that creates a gyrotropic non-reciprocal response. However, the need for an external magnetic bias hinders the integration of such components on a chip. For that reason, metamaterials with time-varying modulations have been investigated as an unconventional solution to obtain asymmetric light flows.
The research developed, so far, by João Serra was mainly focused on two topics:
1 - Topological Characterisation of Spacetime Systems: He has shown that rotating spacetime modulations may be used to engineer topological Chern phases due to the angular momentum provided by the synthetic motion. Furthermore, counterintuitively, he has proven that a synthetic linear momentum bias, e.g., a traveling-wave modulation, can be an exciting new solution to create nontrivial topological phases in photonic systems.
2 - Homogenisation Theory of Spacetime Crystals: He has introduced an effective medium approach to characterise the dynamic response of a generic dispersive spacetime crystal in the long-wavelength limit. He describes the generalisation of the source-driven homogenisation to the case of spacetime crystals.