Bioinspired Toolkit Based on Intermolecular Encoder toward Evolutionary 4D Chiral Plasmonic Materials.

Chiral framework materials offer a promising platform for exploring circularly polarized lasing. However, the creation of chirality in current optical gain framework materials relies on the chirality transfer, which suffers from weak chiral light-matter interactions and thus limits the dissymmetry factors of circularly polarized laser emission. Here, we propose to synthesize homochiral metal-organic frameworks (MOF) from chiral optical gain molecules to enhance chiral light-matter interactions, enabling circularly polarized lasing with large dissymmetry factors. The MOFs are grown controllably into 1D microcrystals to function as Fabry-Pérot cavities providing optical feedback for laser oscillations. In addition, the chiral optical gain molecules in the frameworks exhibit high luminescence efficiencies of ∼88% because the rigid frameworks effectively suppress nonradiative decay, resulting in low-threshold lasing. More importantly, the homochiral optical gain frameworks can enhance chiral light-matter interactions, which allows for circularly polarized laser emission with dissymmetry factors larger than 1.0. Our work establishes a homochiral framework material platform for exploring high-performance circularly polarized lasing.

Molecular chirality is represented as broken mirror symmetry in the structural orientation of constituent atoms and plays a pivotal role at every scale of nature. Since the discovery of the chiroptic property of chiral molecules, the characterization of molecular chirality is important in the fields of biology, physics, and chemistry. Over the centuries, the field of optical chiral sensing was based on chiral light–matter interactions between chiral molecules and polarized light. Starting from simple optics-based sensing, the utilization of plasmonic materials that could control local chiral light–matter interactions by squeezing light into molecules successfully facilitated chiral sensing into noninvasive, ultrasensitive, and accurate detection. In this Review, the importance of plasmonic materials and their engineering in chiral sensing are discussed based on the principle of chiral light–matter interactions and the theory of optical chirality and chiral perturbation; thus, this Review can serve as a milestone for the proper design and utilization of plasmonic nanostructures for improved chiral sensing.

Chirality refers to the structural property of an object that cannot be superposed onto its mirror image. The existence of chirality in nature is universal, ranging from molecules at the nanoscale to gastropod shells at the macroscale. Light can be chiral as well. Circularly polarized light with opposite helicity has its electric field vector rotating clockwise or counterclockwise during propagation. Chiral light-matter interactions are widely used in molecule detection, optical communication and quantum information processing. In this talk, I will discuss how to engineer the chiral light-matter interaction based on metamaterials and nano photonic structures towards novel imaging and sensing applications. I will first present a new concept of chiral metamirrors, which can achieve near-perfect reflection of designated circularly polarized light without reversing its handedness, yet complete absorption of the other polarization state [1]. Such a metamaterial can be used for polarimetric imaging to extract the polarization information of light [2]. Recently, we have applied the deep learning approach to accelerate the design of chiral metamaterials with prescribed chiroptical responses [3]. Finally, I will discuss the generation of chiral hotspots in silicon nanocube dimers that can amplify circular dichroism signals by one order of magnitude [4]. Our findings would lead to integrated devices for circular dichroism spectroscopy, enantioselective sensing, sorting and synthesis.

We study the negative refractive index in cubic noncentrosymmetric superconductors. We consider the Maxwell equations under the Meissner effect, and the magnetoelectric effect arising due to inversion-symmetry breaking. We derive the dispersion relations of electromagnetic waves and show that the refractive index becomes negative at frequencies just below the plasma gap. We find that the chiral mechanism of the negative refractive index, which is usually discussed in chiral materials with negative permittivity, can be directly applied to noncentrosymmetric superconductors with positive permittivity. A rough estimation from experimental values of the penetration depth of LiPt|$_3$|B indicates that a negative refractive index may appear in UV regions.

Three-dimensional chiral materials with intrinsic chirality play a crucial role in achieving a strong chiral response and flexible light manipulation. Reconfigurable chirality through the 3D morphological transformation of chiral materials is significant for greater freedom in tailoring light but remains a challenge. Inspired by the unique 3D morphological memory capability of shape memory alloys (SMAs), we demonstrate and discuss a chiral resonator in the microwave regime that can realize reconfigurable chirality through 3D morphological transformation. The introduction of heating film realizes voltage control of SMA’s morphology for utilizing the temperature sensitivity of SMA better, enabling arbitrary control of circular dichroism (CD) flip and CD intensity. The qualitative and quantitative analysis of the surface current distribution of chiral enantiomers reveals that the chirality of meta-atoms originates from the surge of electric dipole p x and electric quadrupole Q. It is worth mentioning that the proposed strategy to achieve reconfigurable chirality using 3D morphological transformations can be directly extended to other higher frequencies, such as visible, infrared, and terahertz bands. Significantly, our paradigm to study the relationship between complex 3D morphology and chirality holds potential for application in biosensing, spin detection, and spin-selective devices.

Chemical reactions and energy transport phenomena have been experimentally reported to be significantly affected by strong light-matter interactions and vibrational polariton formation. These quasiparticles exhibit nontrivial transport phenomena due to the long-range correlations induced by the photonic system and elastic and inelastic scattering processes driven by matter disorder. In this article, we employ the Ioffe-Regel criterion to obtain vibrational polariton mobility edges and to identify distinct regimes of delocalization and transport under variable experimental conditions of light-matter detuning, disorder, and interaction strength. Correlations between the obtained trends and recent observations of polariton effects on reactivity are discussed, and essential differences between transport phenomena in organic electronic exciton and vibrational polaritons are highlighted. Our transport diagrams show the rich diversity of transport phenomena under vibrational strong coupling and indicate that macroscopic delocalization is favored at negative detuning and large light-matter interaction strength. We also find the surprising feature that, despite the presence of dephasing-induced inelastic scattering processes, macroscopic lower polariton delocalization and wave transport are expected to persist experimentally, even in modes with small photonic weight.

Detecting the chirality of molecules is of great importance in optics, biomedicine, and materials science. In chiroptical spectroscopy, it's crucial to achieve strong chiroptical signals with a minimal number of chiral molecules. The molecular chiroptical signals, however, are typically weak for chiral molecular sensing in conventional circular dichroism using photonic spin angular momentum, even in the presence of a large number of chiral molecules (micromoles to millimoles). Here, by involving chiral light-matter interaction with photonic orbital angular momentum, we demonstrate strong chiroptical responses that reflect the molecular chirality in a single chiral nanoassembly. We experimentally present the helical dichroism spectra of chiral nanoassemblies synthesized from L/D-cystines, consistent with electromagnetic simulations. The asymmetry factors in the fundamental wavelength and photoluminescence emission reach values of 0.53 and 1.18, respectively, exceeding those observed in the circular dichroism mechanism. To improve the dimensions of helical dichroism spectroscopy, we analyze helical dichroism in wavelength domain, polarization domain, and momentum space. Our findings not only expand the methods for trace chiral molecular sensing but also provide insights into chiral light-matter interactions.

The identification and separation of chiral substances are of importance in the biological, chemical, and pharmaceutical industries. Here, we demonstrate that a focused circularly polarized vortex beam can, in the focal plane, selectively trap and rotate chiral dipolar particles via radial and azimuthal optical forces. The handedness and topological charge of the incident beam have strong influence on identifying and separating behavior: left- and right-handed circular polarizations lead to opposite effects on the particle of trapping and rotating, while the sign of topological charge will change the particle's rotation direction. Such effects are a direct result of the handedness and topological charge manifesting themselves in the directions of the spin angular momentum (SAM) and Poynting vector. The research provides insight into the chiral light-matter interaction and may find potential application in the identification and separation of chiral nanoparticles.

Chirality is a property which is widely observed in nature and refers to the characteristic that an object cannot be superimposed on its mirror image. Recently, chiral solution-processable semiconductors have seen a surge of interest for their potential applications in emerging photonic, optoelectronic and spintronic technologies [1]. Yet, the underlying chiral light-matter interactions, especially in the excited state, which lead to spin and light polarization remain poorly understood [2]. Here, we present our preliminary results on employing transient chiroptical spectroscopy to understand the consequences of morphological (hierarchical) chirality for charge, spin and light polarization. We compare achiral chromophores in solution and a solid-state matrix with their arrangement into chiral twisted molecular crystal films with chiral domains and discuss the complex photophysics we observe [3]. By studying chiral light-matter interactions transiently and with high sensitivity we hope to aid in understanding the microscopic origin of chiral-induced spin-selectivity (CISS) observations and other mechanistic approaches that could enable efficient spin and light polarization control using cheap solution- processable semiconductors.

The interaction of circularly polarized light with matter is the basis for molecular circular dichroism spectroscopy, optical spin manipulation, and optical torques. However, chiroptical effects are usually hampered by weak chiral light-matter interaction. Nanophotonic structures can enhance optical intensity to boost interactions, but magnifying chiral effects requires that the near field remains chiral in the process. Here, we propose the conditions, limits and guidelines for enhancing different chiroptical effects near achiral metasurfaces with maximum chirality of the evanescent fields. We illustrate these conditions with arrays of metal and dielectric nanodisks and decompose their distinct electromagnetic metrics into propagating and evanescent Fourier orders. We prove that chirality metrics like circular dichroism and the degree of circular polarization, which go hand-in-hand in the far field for propagating plane waves, are incompatible in the evanescent near field. As a result, a nanostructure cannot be universally optimal for different chirality metrics and therefore applications. For example, arrays tailored for enhanced spin excitation with spatially uniform circular polarization destroy circular dichroism. Conversely, we predict a limit of maximum attainable circular dichroism in highly evanescent Fourier orders through a simple relation with the evanescent wavevector and polarization. We demonstrate that silicon nanodisk arrays can enhance chiral effects within these constraints. Our results define the limits on the ability of nanophotonic platforms to enhance different chiral light-matter interactions simultaneously. Our work provides design rules for diverse chiroptical applications such as molecular spectroscopy, information technology and optical nanomanipulation.

Chirality is a basic property of nature and has great importance in photonics, biochemistry, medicine, and catalysis. This importance has led to the emergence of the chiral inorganic nanostructure field in the last two decades, providing opportunities to control the chirality of light and biochemical reactions. While the facile production of 3D nanostructures has remained a major challenge, recent advances in nanocrystal synthesis have provided a new pathway for efficient control of chirality at the nanoscale by transferring molecular chirality to the geometry of nanocrystals. Interestingly, this discovery stems from a purely crystallographic outcome: chirality can be generated on high-Miller-index surfaces, even for highly symmetric metal crystals. This is the starting point herein, with an overview of the scientific history and a summary of the crystallographic definition. With the advance of nanomaterial synthesis technology, high-Miller-index planes can be selectively exposed on metallic nanoparticles. The enantioselective interaction of chiral molecules and high-Miller-index facets can break the mirror symmetry of the metal nanocrystals. Herein, the fundamental principle of chirality evolution is emphasized and it is shown how chiral surfaces can be directly correlated with chiral morphologies, thus serving as a guide for researchers in chiral catalysts, chiral plasmonics, chiral metamaterials, and photonic devices.

Chiral-structured nanoscale materials exhibit chiroptical properties with preferential absorptions of circularly polarized light. The distinctive optical responses of chiral materials have great potential for advanced optical and biomedical applications. However, the fabrication of three-dimensional structures with mirrored nanoscale geometry is still challenging. This study introduces chiral plasmonic nanopatterns in wavy shapes based on the unidirectional alignment of block copolymer thin films and their tilted transfer, combined with buckling processes. The cylindrical nanodomains of polystyrene-block-poly(2-vinylpyridine) thin films were unidirectionally aligned over a large area by the shear-rolling process. The aligned block copolymer thin films were transferred onto uniaxially prestrained polydimethylsiloxane films at certain angles relative to the stretching directions. The strain was then released to induce buckling. The aligned nanopatterns across the axis of the formed microwrinkles were selectively infiltrated with gold ions. After reduction by plasma treatment, chiral plasmonic nanowave patterns were fabricated with the presence of mirror-reflected circular dichroism spectra. This fabrication method does not require any lithography processing or innately chiral biomaterials, which can be advantageous over other conventional fabrication methods for artificial nanoscale chiral materials.

Multi-partite entanglement is fundamental to emerging quantum technologies, such as quantum networks, which ultimately require devices with strong light–matter interactions and long coherence times. Here, we introduce nanobeam photonic crystal cavities combining both extreme quality factors (∼107) with sub-wavelength field confinement to reach unprecedented light–matter interactions. Operating at 780 nm, our devices are tailored for efficient coupling and entanglement with ultracold 87Rb atoms, a key ingredient in quantum networks due to their hyperfine structure. Our new designs also facilitate the precise optical trapping of atoms, and we demonstrate coherent entanglement generation between them, which is remarkably resilient to atomic displacements. These platforms can be easily scaled-up to extremely large quantum networks, for distributed quantum computing and future light-based quantum technologies.

Surface plasmon polaritons (SPPs) carry transverse optical spin within the evanescent field, which has enabled the demonstration of various chiral light–matter interactions in classical and quantum systems. To achieve high spin selectivity in the interactions, the elliptical polarization of the evanescent field should be made circular, but the engineering principle of the degree of circular polarization (DOCP) of SPPs has been lacking. In this study, we theoretically and numerically investigate the scaling behavior of the DOCP of the SPP field with respect to the modal effective refractive index (neff). The DOCP of the SPP field exhibits power-law scalability to the effective refractive index in the one-dimensional (1D) layered system regardless of the material, structural geometry, and excitation wavelength. The power-law scalability is also confirmed in two-dimensional (2D) waveguide structures for in-plane and out-of-plane SPP fields, but the scaling exponents vary depending on the distance from the waveguide boundaries by the reduced symmetry of the given system. Due to Lorentz reciprocity, the power-law scalability can be extended to the coupling directionality of chiral emitters toward the plasmonic waveguide. To this end, we propose a chiral photonic platform for enhanced light–valley interaction, which utilizes simultaneous enhancement of the DOCP and coupling directionality. An incident SPP can excite a chiral emitter with high spin selectivity that unidirectionally couples the emitted light into the plasmonic waveguide, depending on the valley polarization of excitons in 2D materials. Our work provides a ground rule for designing chiral nanophotonic systems and paves the way for the exploration of scale-free phenomena of electromagnetic waves.

We investigate how the near-field enhancement of self-similar nanolenses, made of three plasmonic nanospheres with decreasing sizes and separations, is affected by quantum corrections in the optical response of the metal and by fabrication imperfections related to the positioning of the spheres in the nanolens. In particular, we integrate mesoscopic phenomena, such as electron spill-in and -out and surface-enabled Landau damping, via the surface-response formalism, focusing particularly on the role of spill-out in alkali metals. In addition, we take realistic imperfections in the nanofabrication process into account, through numerical averaging of both far- and near-field spectra for large collections of nanolenses. Statistical analysis of hundreds of trimers shows that inevitable deviations from the perfectly aligned chain only slightly, if at all, impair the field enhancement, as long as the average misplacement is kept within 1 nm from the ideal situation. Wishing to explore whether such imperfections can be harvested for practical applications, we probe the potential for triggering chiral response. Our results verify that imperfect nanolenses can display considerable light-induced optical activity and circular dichroism, while providing a means to manipulate the optical chirality density. This highlights how promising the nanolensing effect is for chiral light–matter interactions. Nonetheless, we emphasize that quantification of chiral light–matter interactions can be largely affected by mesoscopic phenomena, which cannot be ignored when near-field quantities like optical chirality density are investigated.