Double-Layer Chiral System with Induced Circular Dichroism by Near-Field Coupling

Circular dichroism (CD) is widely used in enantiomer identification, photodetection, and circular polarization devices. Improving the CD signal of easily prepared 3D chiral nanostructures by designing templates remains a challenge in this field. Herein, double-layer nanostructures, which can be prepared with one-time electron beam lithography (EBL) combined with electron beam deposition, are theoretically and experimentally shown to exhibit a CD effect. Theoretical results show that the double-layer nanostructures form strong local electromagnetic fields between the layers due to near-field coupling and that the relative positions of the different parts that break the symmetry of the nanostructures lead to differences in distorted magnetic fields and transmission under circularly polarized light (CPL) excitation, thereby producing CD effects. In addition, modifications in arm positions change the asymmetry of the structure, resulting in large CD effects due to amplified left and right CPL transmission differences. Furthermore, the CD effect can be tuned remarkably by changing the VO2 state to regulate the near-field coupling. These results provide a way to obtain CD effects by using identical nanostructures in the upper and bottom layers and manipulating near-field coupling. Such chiral devices have potential applications in chiral recognition, remote temperature readout, and advanced control of chemical reactions.