Light scattering in resonant nanostructures with broken symmetries: chirality and magneto-optics

Symmetries can be regarded as pivotal when considering physical effects in light matter interactions. Geometrical symmetries are easy to spot just by exploring the shape of the system under consideration. Others, such as reciprocity or time reversal invariance are more subtle to identify. They appear particularly important when exploring scattering properties of resonant systems. Therefore, when looking for novel, or peculiar light-matter interactions systems with broken symmetries are attracting lots of attention.   In the recent years the phenomenon of magneto-plasmonics revolved around the broken time reversal invariance upon the presence of an external, static magnetic field, giving rise to a plethora of different effects, both involving enhancement of the magneto-optical effect via resonances or the control of resonances via the magneto-optical effect. [1,2]   Additionally, systems without mirror symmetry, more precisely those exhibiting a clear sense of twist or handedness are called chiral. Chirality is a concept that is embedded in our live, since a large amount of biological molecules, such as amino acids or proteins, are chiral.[3] Normally the signature of handedness is weak, and therefore resonant systems, presenting chirality or interacting with the chiral species have been attracting lots of attention.[4]   In this talk I will give an overview of, what I personally consider, the most relevant aspects of both chirality and magneto-optics, putting forward some key elements to get simple rule of thumbs to understand the physics behind. Then I will connect those with a couple of our latest works on magneto-optical control of bound-states in the continuum in metasurfaces [5] and chirality from interacting achiral elements[6].   [1] G. Armelles et al., Advanced Optical Materials 1, 10-35 (2013) [2] N. Maccaferri, et al. J. Appl. Phys. 127, 080903 (2020) [3]L. D. Barron, Molecular Light Scattering and Optical Activity, Cambridge, Cambridge Univeristy Press, (2004) [4] S. Collina, Chirality 34, 1491 (2022). [5] D.R. Abujetas, et al., Nanophotonics 10, 42232 (2021). [6] B. Castillo López de Larrinzar, et al., Nanophotonics 12, 1957 (2023)