Quantifying Fano properties in self-assembled metamaterials

Abstract

Fano resonances in metamaterials can be explained by the coupling between different modes sustained by the meta-atom. While the associated spectral features are usually quite easy to identify for top-down metamaterials, thanks to the deterministic arrangement of the meta-atom relative to the illumination, the identification of spectral features due to Fano resonances is much more challenging for bottom-up metamaterials. There, the response is spurred by the random arrangement of the meta-atoms relative to the illumination. To improve the situation, we introduce a quantity that measures the nonorthogonality of the modes sustained by the meta-atom. The measure allows us to disclose whether specific details in the spectral response emerge from Fano features or whether they are only due to the incoherent superposition of different modes. We strengthen our argumentation while discussing the multipolar decomposition of the different modes that contribute to the Fano features for a representative meta-atom.

Describing Meta-Atoms Using the Exact Higher-Order Polarizability Tensors

“…In addition, the reciprocity enforces (α e2 m1 ) xy z = (α m1 e2 ) z xy . Interestingly, (α m1 m1 ) z z , (α e2 e2 ) xy xy , and (α m1 e2 ) z xy have very similar spectral feature resembling Lorentzian resonances, indicating that some components may additionally be coupled together possibly using singular value decomposition technique [10] or modular analysis [47]. Plasmonic chiral particles have exhibited chiral responses far-exceeding those from natural materials.…”

“…Because the meta-atom is strong anisotropic, its α -tensor is simplified in the Cartesian basis. Interestingly, (α m1 m1 ) z z , (α e2 e2 ) xy xy , and (α m1 e2 ) z xy have very similar spectral feature resembling Lorentzian resonances, indicating that some components may additionally be coupled together possibly using singular value decomposition technique or modular analysis …”

“…Earlier studies have usually incorporated small spheres, whose α can be easily obtained using the quasistatic approximation (see section S7 of Supporting Information for more details) to study their interaction with light and with nearby scattering objects or molecules. , However, meta-atoms with a complicated multipolar transitions can also be modeled into α -tensors, which are then inserted into the MST, potentially allowing studies on more complicated physics, for example, Fano resonances , and hybridization of particle and lattice resonances in 2D ,,, and 3D , arrays. In this section, we reconstruct several physical phenomena arising in electromagnetically coupled meta-atoms simply by implementing α -tensors into the MST and discuss the advantages of this method.…”

“…Manipulation of light in the nanoscale has been facilitated by the interference of multipole radiations, which provides the underlying principles behind many optical phenomena and relevant applications. Notably, the multipole framework has given insights on directional scattering, lattice Kerker effects, nonradiating anapoles, , lattice invisibility effects, Fano-like resonances, , optical antiferromagnetism, optical nonlinearity, radiative heat transfer, weak localization, photonic topological insulators, and bound states in the continuum …”

Extremize Optical Chiralities through Polarization Singularities

“…Chiral effects can be observed for both intrinsically chiral and achiral structures [3][4][5][6][7]. As for chiral structures, (intrinsic) chiralities are generally present and can be quantified as directionindependent properties through orientation-averaging chiral effects [1,2,[8][9][10][11]; while for achiral structures, (extrinsic) chiralities are manifest for some symmetry-breaking incident directions [12][13][14][15][16], which nevertheless would be extinguished for symmetry-preserving directions or when orientation-averaged. For both scenarios, chiral responses are generally dependent on structure orientations, and thus it is interesting and significant to clarify systematically how chiralities can be extremized with respect to incident directions.…”