Recent progress on artificial propeller chirality and related circular dichroism engineering

Abstract

<p indent="0mm">Chirality, a geometric asymmetry in which a structure cannot coincide with its own mirror image through rotation and translation, is one of the basic properties of nature. It has been involved in all aspects of our life, such as art, architectural design, medicine, pesticides, life, information, chiral optoelectronic functional materials and devices. The interactions of chiral substances with light can differ for left- and right-handed circularly polarized (LCP and RCP) light and rely on the handedness of the enantiomers. Since scientists discovered the optical activity of chiral matter in the 19th century, the study of chiral light-matter interactions has become one of the most cutting-edge research fields in optics. Circular dichroism (CD) is the difference in absorption of LCP and RCP light by chiral substances. Since the chiral optical response of natural chiral matter is weak and difficult to tune, researchers have creatively designed various artificial chiral structures to enhance chiral light-matter interactions and realize many novel physical phenomena. The most common example is the helical configuration, which can be seen as the result of the stretched superposition of multiple split resonator rings. It can obtain much larger CD than natural materials. However, the three-dimensional fabrication process of micro/nanoscale helical structures faces challenges, which limit its application research. Different from common helical chiral structures and based on the nano-kirigami fabrication technique, this review focuses on a new type of artificial propeller-like chiral micro/nanostructures and their applications in chiral optics. This artificial propeller chirality is quite different from the traditional chiral structure in terms of geometric morphology and physical responses, such as the novel out-of-plane stereo twist and the chiral competition mechanism enabled by the hybridization of unit cells with two different chiral centers. The CD responses can be significantly enhanced by the chiral Fano resonance that is caused by the surface lattice resonances (SLRs). The chiral SLRs are formed by the coupling of chiral electric quadrupole modes to the diffractive lattice mode (Rayleigh anomaly). These unique features enable outstanding advantages in the flexible manipulation of optical CD, including the sensitive changes in intensity, sign and wavelength upon structural perturbations. Specially, the counterintuitive sign reversal of CD can be realized under minor structural changes without inverting the handedness of artificial propeller chirality. The work in this review provides a novel design idea for new artificial chiral micro/nanostructures and an ideal platform for in-depth study of chiral physics.