Localization of light in disordered topological metamaterials – LOLITOP

We will use a flexible microwave experimental platform to investigate Anderson localization in topologically nontrivial 2D metamaterials and to demonstrate a TAI in gyromagnetic or non-uniformly strained materials. The experimental activity will benefit from a solid theoretical support both at the stage of experiment design and for interpretation of results. A separate theoretical study will aim at extending the 2D analysis to higher dimensions (3D, 4D). Owing to the scaling of Maxwell equations with frequency, our results will apply beyond the microwave frequency range and will open a door to novel designs of nano-structured optical metamaterials. We will reach various propagation regimes in our experimental setup composed of dielectric resonators that can be equipped with patches of magnetic material for controlling the time-reversal symmetry in light propagation by an external magnetic field. The freedom in the choice of the spatial arrangement of resonators allows for designing photonic metamaterials with ordered, disordered, or quasi-periodic structure. The expected results of the project include the understanding of the interplay between topology and disorder in 2D photonic metamaterials, the theoretical description and experimental realization of the first 2D photonic TAI based on the use of gyromagnetic materials, the theoretical description and experimental realization of the first 2D photonic pseudo-TAI making use of a nonuniform lattice deformation, the theoretical description of the first quasi-periodic 2D photonic TAI, and the theoretical investigation of a 3D photonic TAI to motivate future experiments.

Expected results:
- Understanding of the interplay between disorder and topology in photonics
- Experimental realization and theoretical modelling of the first optical TAI in 2D
- Theoretical study of the possibility to achieve an optical TAI in 3D

In the short-time perspective, the LOLITOP project is expected to have a strong impact on fundamental research in optics, electromagnetism, and more generally, wave propagation in complex media. In the mid-term, our results will help to advance knowledge in condensed-matter physics in general. Finally, in addition to addressing fundamental questions, the LOLITOP project will contribute to the development of new optical technologies. Better understanding of the combined impact of disorder and topology on wave propagation is expected to allow for their controlled use in order to create useful functionalities and thus to pave a way towards future functional optical materials in the long term.

S.E. Skipetrov and P. Wulles, Topological transitions and Anderson localization of light in disordered atomic arrays, Phys. Rev. A 105, 043514 (2022)

The main objective of the LOLITOP project is to study the interplay between topological physics and disorder-induced effects for light in two-dimensional (2D) metamaterials made of subwavelength resonators. On the one hand, disorder may induce a topologically nontrivial phase – the so-called topological Anderson insulator (TAI). On the other hand, the properties of disorder-induced spatially localized states with energies inside band gaps may depend on the topological indices of adjacent energy bands. We will use a flexible microwave experimental platform to investigate Anderson localization in topologically nontrivial 2D metamaterials and to demonstrate a TAI in gyromagnetic or non-uniformly strained materials. The experimental activity will benefit from a solid theoretical support both at the stage of experiment design and for interpretation of results. A separate theoretical study will aim at extending the 2D analysis to higher dimensions (3D, 4D). Owing to the scaling of Maxwell equations with frequency, our results will apply beyond the microwave frequency range and will open a door to novel designs of nano-structured optical metamaterials.

The main innovation of the LOLITOP project with respect to the state of the art is the full consideration given to the aspects specific to photonics (polarization of light, resonant nature of scattering, possibility of strong deformations of a lattice) in the study of the impact of disorder on light propagation in topologically nontrivial metamaterials. The main scientific barriers to overcome are due to the needs of adapting the methodology existing to deal with electronic systems to vector electromagnetic waves, and of coping with the fundamental differences between photons and electrons: the absence of charge and the “volatility” of photons that can easily leave the material or be absorbed by it. Fortunately, these difficulties also open a number of new opportunities arising from the possibility of manipulating the polarization of electromagnetic waves (TM or TE) and controlling the number of modes allowed to propagate inside the metamaterial. We will fully exploit these opportunities to reach various propagation regimes in our experimental setup composed of dielectric resonators that can be equipped with patches of magnetic material for controlling the time-reversal symmetry in light propagation by an external magnetic field. The freedom in the choice of the spatial arrangement of resonators allows for designing photonic metamaterials with ordered, disordered, or quasi-periodic structure. The expected results of the project include the understanding of the interplay between topology and disorder in 2D photonic metamaterials, the theoretical description and experimental realization of the first 2D photonic TAI based on the use of gyromagnetic materials, the theoretical description and experimental realization of the first 2D photonic pseudo-TAI making use of a nonuniform lattice deformation, the theoretical description of the first quasi-periodic 2D photonic TAI, and the theoretical investigation of a 3D photonic TAI to motivate future experiments.

In the short-time perspective, the LOLITOP project is expected to have a strong impact on fundamental research in optics, electromagnetism, and more generally, wave propagation in complex media. In the mid-term, our results will help to advance knowledge in condensed-matter physics in general. Finally, in addition to addressing fundamental questions, the LOLITOP project will contribute to the development of new optical technologies. Better understanding of the combined impact of disorder and topology on wave propagation is expected to allow for their controlled use in order to create useful functionalities and thus to pave a way towards future functional optical materials in the long term.