Manipulating the Chirality of Moiré Metasurface by Symmetry Breaking

Abstract

The chirality of materials is of great significance in many fields. Metasurfaces with chirality have attracted great attention in the past decades because of their ability to miniaturize the device into the nanoscale. An important class of chiral metasurfaces is the Moiré pattern assembled by two layers of metasurfaces. However, Moiré metasurfaces usually have limited circular dichroism. Here, the origin and the limiting factor of the chirality of Moiré metasurfaces using the chiral coupled oscillator model is analyzed. It is demonstrated that, with the help of a non-Hermitian Hamiltonian, the chirality can be improved by breaking the symmetry in the positive and negative k directions. The best result is achieved when both the two components have lowest transmission. In addition, the chiral anisotropy of a Moiré metasurface in full momentum space is studied, and it is shown that the chirality can be further improved in certain directions. The chiral anisotropy of Moiré metasurfaces may be used in applications such as optical information storage, structured color, unidirectional light coupling, sensitive chiral sensors, chiral nonlinear optics, chiral lasers, and Bose-Einstein condensation.

Ultrathin Twisted Stacked Gap‐Plasmon Metasurface with Giant and Tunable Shortwave Infrared Chirality

“…The large figure of merit (FoM) stands among the highest values ever‐reported for chiral metamaterials that function in the NIR/SWIR (Figure 1e). [ 32–45 ]…”

Nonlocal Metasurface with Chiral Exceptional Points in the Telecom-Band

“…First, the refractive index and thickness variations in the structural substrate (silica) and coating layer (PVA) introduce slight 3D chirality. The refractive indexes of silica and PVA are 1.45 and 1.52, respectively, with thicknesses of 500 μm and 300 nm, respectively. , Second, the deposition and lift-off processes during electron beam lithography (EBL) contribute to a slight difference in the shapes of the upper and lower surfaces of the Au nanorods, introducing additional 3D chirality. In addition, for the bare structure without a PVA coating, the PT symmetry phase transition is observed at 1324 nm experimentally (see details in Supporting Information, Section S5).…”