/pdf/bound-states-in-the-continuum-in-resonant-nanostructures-an-1ddtdo5xqr.pdf

Bound states in the continuum in resonant nanostructures: an overview of engineered materials for tailored applications

Nanoscopic chiroptics studies the spin-dependent asymmetric light–matter interactions at the nanoscale, where the asymmetry can stem from the intrinsic properties of materials, structures, light or combinations thereof. With the emergence of low-dimensional materials platforms, such as metasurfaces, transition metal dichalcogenides and perovskites, nanoscopic chiroptics has been extended from the far field to the near field, and further developed from the spatial dimension, to the momentum dimension and the integrated spatial–momentum dimension. This expansion of nanoscopic chiroptics across dimensions has uncovered new physical mechanisms and manifestations of chiral effects. It also led to applications such as valleytronics, chiral sensing and chiral photochemistry. This Perspective focuses on the progress in nanoscopic chiroptics through the lens of the associated dimensionalities, discussing the opportunities in integrated optics, photochemistry, quantum optics and biochemical synthesis and analysis. Nanoscopic chiroptics studies the spin-dependent asymmetric light–matter interactions at the nanoscale, where the asymmetry can stem from the intrinsic properties of materials, structures or light. This Perspective establishes an overarching framework for nanoscopic chiroptics across the spatial, moment and integrated spatial–momentum dimensions, and discusses applications enabled by this approach.

Multidimensional nanoscopic chiroptics

Two-dimensional (2D) layered materials such as GaSe recently have emerged as novel nonlinear optical materials with exceptional properties. Although exhibiting large nonlinear susceptibilities, the nonlinear responses of 2D materials are generally limited by the short interaction lengths with light, thus further enhancement via resonant photonic nanostructures is highly desired for building high-efficiency nonlinear devices. Here, we demonstrate a giant second-harmonic generation (SHG) enhancement by coupling 2D GaSe flakes to silicon metasurfaces supporting quasi-bound states in the continuum (quasi-BICs) under continuous-wave (CW) operation. Taking advantage of both high-quality factors and large mode areas of quasi-BICs, SHG from a GaSe flake is uniformly enhanced by nearly 4 orders of magnitude, which is promising for high-power coherent light sources. Our work provides an effective approach for enhancing nonlinear optical processes in 2D materials within the framework of silicon photonics, which also brings second-order nonlinearity associated with 2D materials to silicon photonic devices.

Giant Enhancement of Continuous Wave Second Harmonic Generation from Few-Layer GaSe Coupled to High-Q Quasi Bound States in the Continuum.

Chiral degrees of freedom occur in matter and in electromagnetic fields and constitute an area of research that is experiencing renewed interest driven by recent observations of the chiral-induced spin selectivity (CISS) effect in chiral molecules and engineered nanomaterials. The CISS effect underpins the fact that charge transport through nanoscopic chiral structures favors a particular electronic spin orientation, resulting in large room-temperature spin polarizations. Observations of the CISS effect suggest opportunities for spin control and for the design and fabrication of room-temperature quantum devices from the bottom up, with atomic-scale precision. Any technology that relies on optimal charge transport, including quantum devices for logic, sensing, and storage, may benefit from chiral quantum properties. These properties can be theoretically and experimentally investigated from a quantum information perspective, which is presently lacking. There are uncharted implications for the quantum sciences once chiral couplings can be engineered to control the storage, transduction, and manipulation of quantum information. This forward-looking perspective provides a survey of the experimental and theoretical fundamentals of chiral-influenced quantum effects, and presents a vision for their future roles in enabling room-temperature quantum technologies. 

/pdf/a-chirality-based-quantum-leap-2fez7rc4.pdf

A Chirality-Based Quantum Leap

This review presents the main techniques employed to construct chiral plasmonic materials and metasurfaces, in particular using soft-chemistry approaches, and discusses some applications of these nanostructures.

/pdf/chiral-plasmonic-nanostructures-recent-advances-in-their-21qvwtkf.pdf

Chiral plasmonic nanostructures: recent advances in their synthesis and applications

Circular dichroism (CD) spectroscopy is conventionally utilized for the enantiomer-specific analysis of chiral samples, which is of great significance in academia and industry. Recently, metasurfaces have been introduced for enhancing the sensitivity of CD spectroscopy. However, the obtained CD spectrum alone cannot provide the enantiomer composition of a chiral sample. It should be normalized by the molar concentration of chiral molecules, which is usually measured on a different platform. Here, for the first time we demonstrate the integrated acquisition of CD spectrum and molar concentration over an individual metasurface with high sensitivities. High-Q resonances are supported on the metasurface, governed by bound states in the continuum. The generated superchiral field enables a 59-times enhancement of CD signal. Meanwhile, the refractive index-based detection of molar concentration achieves a large figure-of-merit of 80.6. Accordingly, a standard procedure is established for the integrated molar chiral sensing with high sensitivity.

Chen Zhao

Papers

Integrated Molar Chiral Sensing Based on High-Q Metasurface