Chiroptical Response of Geometrically Symmetric Nanoscopic Heterostructures

Chiral objects lack geometric mirror symmetry and thus can exist in two mirror-imaged forms, called enantiomers, distinguishable via their interaction with circularly polarized light [Nature 222, 426–431 (1969)].Recently, we... [ view full abstract ]

Chiral objects lack geometric mirror symmetry and thus can exist in two mirror-imaged forms, called enantiomers, distinguishable via their interaction with circularly polarized light [Nature 222, 426–431 (1969)].

Recently, we proposed a novel concept for inducing a chiroptical response by breaking the in-plane symmetry of a nanostructure by a heterogeneous material composition, rather than geometry [Nat. Commun. 7, 13117 (2016)]. We investigated an individual ensemble of three equally sized spherical nanoparticles of different materials (“trimer”, Fig. 1) fabricated using a custom-developed pick-and-place technique [10.1364/CLEO_SI.2014.STu1H.1]. This geometrically mirror symmetric heterostructure shows differential absorption of normally incident circularly polarized light of opposite handedness.

Here, with the aid of k-space polarimetry, we perform complete Mueller matrix spectroscopy of this individual nanostructure. Employing full polarimetric analysis allows for quantifying the contributions of circular birefringence and circular dichroism to the chiroptical response, separated from linear dichroism and linear birefringence. We theoretically and experimentally demonstrate that the interaction of an individual geometrically mirror-symmetric heterostructure with a substrate transforms the morphology of the system from 2D to 3D chiral.

In summary, we elucidate chiroptical effects of resonant heterostructures in theory and experiment [arXiv:1804.04056]. Our findings open new avenues for designing novel chiral media with a material degree of freedom to precisely tailor the chiroptical response over a broad spectral range. In this perspective, we envision the impact of our results on studies of chiral response of molecules and nanostructures, immobilized on substrates.

Fig. 1: Sketch of the heterogeneous trimer composed of gold and silicon
nanospheres, deposited on a glass substrate (inset: SEM image).