Chiral Photonic Super-Crystals Based on Helical van der Waals Homostructures

Chirality is one of the most mysterious symmetry transformations. Very readily broken in biological systems, it is practically absent in naturally occurring inorganic materials and is very challenging to create artificially. Chiral optical wavefronts are often used for the identification, control, and discrimination of left- and right-handed biological and other molecules. Thus, it is crucially important to create materials capable of chiral interaction with light, which would allow one to assign arbitrary chiral properties to a light field. This study utilizes van der Waals technology to assemble helical homostructures with chiral properties (e.g., circular dichroism). Because of the large range of van der Waals materials available, such helical homostructures can be assigned with very flexible optical properties. The approach is demonstrated by creating helical homostructures based on multilayer As2S3${\rm As}_2{\rm S}_3$ (arsenic trisulfide), which offers the most pronounced chiral properties even in thin structures due to its strong biaxial optically anisotropy. The work showcases that the chirality of an electromagnetic system may emerge at an intermediate level between the molecular and the mesoscopic one due to the tailored arrangement of non-chiral layers of van der Waals crystals and without additional patterning. Chirality is a geometrical property of 3D objects that not only profoundly affects the optical properties of matter, but also can be the key to understanding many biological processes. This study presents a novel platform for the design of helical nanostructures possessing strong chiroptical response based on thin layers of a non-chiral van der Waals material. image