Three-dimensional Chiral Structure Research Articles

Realization of exciton-polariton optical chirality based on strong coupling between intrinsic chiral quasibound states in the continuum and monolayer WS2.

Hybrid quasiparticles produced by the strong interaction between nanostructures and excitons will exhibit optical chirality when one of the coupled components is chiral. Due to the tunability of hybrid states, the coupled system has potential applications in chiral devices and chiral sensing. However, reported chiral materials including chiral molecules and three-dimensional chiral structures in the coupled system limit the application due to the weak chiroptical responses and difficult fabrication, respectively. In this paper, we design chiral quasibound states in the continuum (q-BIC) metasurface by introducing planar symmetry-breaking and z-axis perturbation into an array structure whose unit cell is a C4 rotational symmetric disk. By tuning the polarization state of the eigenmode, a significant chiroptical response is obtained in our q-BIC metasurface. Furthermore, mode splitting is observed not only in the reflection spectrum but also in the circular dichroism (CD) spectrum in the chiral q-BIC and monolayer WS2 strong coupling system, which indicates the realization of the exciton-polariton optical chirality. More importantly, one order of magnitude difference in the reflection to left and right circularly polarized light is achieved resulting in significant CD signals. Our work provides a new strategy to realize the exciton polaritons with significant chiroptical responses, which exhibits promising applications in on-chip chiral devices.

Left-handed cardiac looping by cell chirality is mediated by position-specific convergent extensions

In the embryonic heart development of mammals and birds, a straight initial heart tube undergoes left-handed helical looping, which is a remarkable and puzzling event. We are interested in the mechanism of this chiral helical looping. Recently, observations were reported that myocardial cells in the embryonic chick heart show intrinsic chirality of rotation. The chirality of myocardial cells, via anisotropic polarization of Golgi inside the cells, leads to a left-right (LR) asymmetry of cell shape. On cell boundaries of LR asymmetric cells, phosphorylated myosin and N-cadherin are enriched. Such LR asymmetric cellular circumstances lead to a large-scale three-dimensional chiral structure, the left-handed helical loop. However, the physical mechanism of this looping is unclear. Computer simulations were performed using a cell-based three-dimensional mathematical model assuming an anterior-rightward-biased contractile force of the cell boundaries on the ventral surface of the heart (orientation of a clock hand pointing to 10 to 11 o’clock). An initially straight heart tube was successfully remodeled to the left-handed helical tube via frequent convergent extension (CE) of collective cells, which corresponds to the previously reported observations of chick heart development. Although we assumed that the biased boundary contractile force was uniform all over the ventral side, orientations of the CEs became position specific on the anterior, posterior, right, and left regions on the ventral tube. Such position-specific CEs produced the left-handed helical loop. In addition, our results suggest the loop formation process consists of two distinct phases of preparation and explicit looping. Intrinsic cell properties of chirality in this investigation were discussed relating to extrinsic factors investigated by other researches. Finally, because CE is generally exerted in the axial developmental process across different animal species, we discussed the contribution of CE to the chiral heart structure across species of chick, mouse, Xenopus, and zebrafish.

Enhanced circular dichroism and biosensing application of planar chiral nanostructure by covering graphene nanobelts

Circular dichroism (CD) of plasmonic nanostructures has broad application prospects, including negative refraction, chemical analysis, and biosensing. Compared with three-dimensional chiral structures, planar chiral structures with easy preparation show a weak CD effect. In this study, graphene nanobelts (GNs) were introduced into planar chiral structures composed of the IL-shaped chiral nanostructures (ILCNs) to enhance the effect of CD. The simulation results showed that the enhancement of CD was obtained from the plasmonic coupling between ILCNs and GNs. It led to different enhancements of the absorption under different circularly polarized lights. The bonding mode, anti-bonding mode, and trapping mode were used to interpret the coupling between the nanorods in ILCNs/GNs. The electromagnetic loss distributions of ILCNs/GNs showed that the electromagnetic loss was transferred from the metal part to the graphene part. The CD spectra of ILCNs with different graphene nanostructures revealed that the enhancements of absorption and CD mostly depended on the graphene belt located in the gaps of ILCNs. Meanwhile, the CD effect strongly depended on the geometric parameters of ILCNs/GNs. Besides, the CD spectra for chiral molecules could be enhanced by ILCNs/GNs under a different handedness. The maximum enhancement factor was 3200 times in the near-infrared band. These results might help explore the mechanism of CD enhancement and promote the application of the planar chiral structure in biosensing.

Half-hedgehog spin textures in sub-100 nm soft magnetic nanodots.

Topologically non-trivial structures such as magnetic skyrmions are nanometric spin textures of outstanding potential for spintronic applications due to their unique features. It is well known that Néel skyrmions of definite chirality are stabilized by the Dzyaloshinskii-Moriya exchange interaction (DMI) in bulk non-centrosymmetric materials or ultrathin films with strong spin-orbit coupling at the interface. In this work, we show that soft magnetic (permalloy) hemispherical nanodots are able to host three-dimensional chiral structures (half-hedgehog spin textures) with non-zero tropological charge. They are observed at room temperature, in absence of DMI interaction and they can be further stabilized by the magnetic field arising from the Magnetic Force Microscopy probe. Micromagnetic simulations corroborate the experimental data. Our work implies the existence of a new degree of freedom to create and manipulate complex 3D spin-textures in soft magnetic nanodots and opens up future possibilities to explore their magnetization dynamics.

Amino-acid- and peptide-directed synthesis of chiral plasmonic gold nanoparticles

Understanding chirality, or handedness, in molecules is important because of the enantioselectivity that is observed in many biochemical reactions 1 , and because of the recent development of chiral metamaterials with exceptional light-manipulating capabilities, such as polarization control2-4, a negative refractive index 5 and chiral sensing 6 . Chiral nanostructures have been produced using nanofabrication techniques such as lithography 7 and molecular self-assembly8-11, but large-scale and simple fabrication methods for three-dimensional chiral structures remain a challenge. In this regard, chirality transfer represents a simpler and more efficient method for controlling chiral morphology12-18. Although a few studies18,19 have described the transfer of molecular chirality into micrometre-sized helical ceramic crystals, this technique has yet to be implemented for metal nanoparticles with sizes of hundreds of nanometres. Here we develop a strategy for synthesizing chiral gold nanoparticles that involves using amino acids and peptides to control the optical activity, handedness and chiral plasmonic resonance of the nanoparticles. The key requirement for achieving such chiral structures is the formation of high-Miller-index surfaces ({hkl}, h ≠ k ≠ l ≠ 0) that are intrinsically chiral, owing to the presence of 'kink' sites20-22 in the nanoparticles during growth. The presence of chiral components at the inorganic surface of the nanoparticles and in the amino acids and peptides results in enantioselective interactions at the interface between these elements; these interactions lead to asymmetric evolution of the nanoparticles and the formation of helicoid morphologies that consist of highly twisted chiral elements. The gold nanoparticles that we grow display strong chiral plasmonic optical activity (a dis-symmetry factor of 0.2), even when dispersed randomly in solution; this observation is supported by theoretical calculations and direct visualizations of macroscopic colour transformations. We anticipate that our strategy will aid in the rational design and fabrication of three-dimensional chiral nanostructures for use in plasmonic metamaterial applications.

Optical Circular Conversion Dichroism via Heterogeneous Planar Nanoplasmonic Metasurface

Chirality as a physical phenomenon originating from lacking mirror symmetry in many natural substances exposes fascinating optical activities, including circular dichroism (CD) and optical circular conversion dichroism (O-CCD). While naturally occurring chiroptical properties are negligible in real substances, boosting these properties to significant levels is one of the main challenges for designing functional photonic and optoelectronic devices. Here, we introduce a new paradigm for the realization of planar metasurfaces with substantial O-CCD, reporting that considerable chiral effects of three-dimensional chiral structure are practically provided by feasible metasurfaces by picking out nanooscillators with strong near-field interaction, different optical properties including loss and radiation, and high overlap between their spectral positions. We apply this concept to heterogeneous nanoplasmonic structures, composed of L-pair of Au–Ag nanorods, as archetypical configurations for substantially raising dichroism compared to materially homogenous ones, i.e., Au–Au and Ag–Ag pairs with different length, respectively. The essential prerequisite for phase lag associated with the third dimension along lightwave propagation is compensated by proposed heterogeneity in metasurface design. Theoretical findings based on the simple hybridization model are adequately supported by the computational results.

Robust and adjustable C-shaped electron vortex beams

Wavefront engineering is an important quantum technology, often applied to the production of states carrying orbital angular momentum (OAM). Here, we demonstrate the design and production of robust C-shaped beam states carrying OAM, in which the usual doughnut-shaped transverse intensity structure of the vortex beam contains an adjustable gap. We find that the presence of the vortex lines in the core of the beam is crucial for maintaining the stability of the C-shape structure during beam propagation. The topological charge of the vortex core controls mainly the size of the C-shape, while its opening angle is related to the presence of vortex–anti-vortex loops. We demonstrate the generation and characterisation of C-shaped electron vortex beams, although the result is equally applicable to other quantum waves. C-shaped electron vortex beams have potential applications in nanoscale fabrication of planar split-ring structures and three-dimensional chiral structures as well as depth sensing and magnetic field determination through rotation of the gap in the C-shape.

Tunable circular polarization conversion and asymmetric transmission of planar chiral graphene-metamaterial in terahertz region

Two-dimensional chirality induced polarization conversion and asymmetric transmission have great potential for polarization applications. We propose graphene-based planar chiral metamaterial and its complementary structure with dual functionality of both circular polarization conversion and asymmetric transmission in terahertz (THz) region. The conversion efficiency of chiral structure can reach up to 37.33/λ, which is comparable with three-dimensional chiral structure made of metal due to the unique optoelectronic properties of graphene. The transmission asymmetry of complementary chiral metamaterial originating from the high order plasmonic resonance can be tuned from 0.049% to 3.504% by changing Fermi energy, and the asymmetry can also be enhanced via geometrical optimization. This work raises the prospect of switchable, compact, and on-chip THz polarized devices with graphene materials.

Transformation of One-Dimensional Achiral Structure to Three-Dimensional Chiral Structure: Mechanistic Study and Catalytic Activities of Chiral Structure.

We have isolated two copper-based coordination polymers through solvent diffusion and solvothermal methods using copper salt, furan dicarboxylic acid (FDC), 4,4'-bipyridine (bpy) in MeOH/ethylene glycol, and water solvents. Compound 1 is adopting P21/c space group and adopts a one-dimensional wirelike structure with a free carboxylate anion. Compound 2 crystallizes in chiral space group P65. This is a three-dimensional structure with helical chains. This helicity might be the reason for chiral generation and symmetry breaking. We have converted compound 1 to compound 2 using grinding, followed by a solvothermal method. The circular dichroism data of 2 showed that it is an enantioenriched compound. We have shown that compound 2 is a very good catalyst for chemo- and regioselective enamination reaction and for azide-alkyne Huisgen cycloaddition, respectively.

In Situ Hydrothermal Synthesis, Crystal Structure, and Properties of a New Inorganic Holmium–Sulfate Coordination Polymer

A new chiral holmium–sulfate coordination polymer, {Ho4(OH)4(SO4)4(H2O)3}n (1), has been synthesized and characterized by elemental analysis, IR and single-crystal X-ray diffraction. The X-ray diffraction analysis reveals that 1 crystallizes in orthorhombic space group P212121 and exhibits a unique three-dimensional chiral structure, in which {Ho4} building blocks are linked by SO42– anions to form a high connected binodal network. Furthermore, thermal and luminescence properties of 1 are investigated in the solid state.

Circular polarization induced by the three-dimensional chiral structure of human sweat ducts.

The upper part of the human eccrine sweat ducts, embedded within the epidermis layer, have a well-defined helical structure. It was recently suggested that, as electromagnetic entities, the sweat ducts interact with sub-mm waves [Y. Feldman et al., Phys. Rev. Lett. 100, 128102 (2008)]. Although correlation between changes in the reflectance spectrum in this frequency range and physiological activities has been shown, a direct link between the electromagnetic reflection and the helical structure itself has remained to be established. The fact that the sweat ducts manifest natural homochirality is henceforth used to produce this link. We report the detection of circular polarization asymmetry in the electromagnetic reflection from the human skin at sub-THz frequencies in vivo. We compare the results to numerical simulations and to measurements of a fabricated metamaterial. We argue that the observed circular dichroism can be interpreted uniquely as the signature of the helical structure itself. By twisting reflected electromagnetic waves, the human skin exhibits properties which are usually discussed only in the framework of metamaterial science.

LAYER MULTIPLE SCATTERING CALCULATIONS FOR NONRECIPROCAL PHOTONIC STRUCTURES

We present an extension of the layer-multiple-scattering method to photonic crystals of gyrotropic spheres in a homogeneous host medium. The efficiency of the method is demonstrated on specific examples of three-dimensional chiral structures and surfaces of crystals of plasma spheres in an external static uniform magnetic field that lack, simultaneously, time-reversal and space-inversion symmetries, and exhibit a nonreciprocal spectral response.

Nonreciprocal optical response of helical periodic structures of plasma spheres in a static magnetic field

A detailed and rigorous theoretical investigation of the optical properties of a generic three-dimensional chiral structure of plasma spheres, without and under the action of an external static uniform magnetic field, is presented. Corresponding photonic band diagrams in conjunction with relevant transmission spectra, calculated by the full electrodynamic layer-multiple-scattering method properly extended to the case of gyrotropic spherical scatterers, are discussed in the light of the theory of nonsymmorphic space groups. This analysis provides a consistent interpretation of some remarkable features and effects like Dirac points, polarization-dependent transmission, as well as band splitting and non-reciprocal optical response that emerge as a result of time-reversal-symmetry breaking, induced by the external static magnetic field, and the lack of space-inversion symmetry in the crystal.

Dynamics of photo-induced terahertz optical activity in metal chiral gratings

We investigated the dynamics of photo-induced optical activity of metal chiral gratings on an Si substrate for terahertz (THz) waves. We employed a new technique that enables optical-pump and THz-probe measurements via broadband THz spectroscopy at the microsecond time scale using a low-repetition-rate pump and a high-repetition-rate probe. We revealed that the THz optical activity decays as a result of the carrier diffusion effect because this optical activity is because of the presence of three-dimensional chiral structures of photo-carriers in the Si substrate.

Hydrothermal Synthesis, Crystal Structure and Luminescent Properties of a Three Dimensional Polyoxometalate-Based Supramolecular Structure: [CuI(phen)2]4[HPW11.5 VICu0.5 IIO40

A polyoxometalate-based complex [Cu I (phen)2]4[HPW11.5 VI Cu0.5 II O40] (1) (phen = 1,10-phenathroline) has been synthesized by hydrothermal method and characterized by IR, elemental analysis, TG technique and X-ray crystallography. [Cu I (phen)2]+ ion balances the charge on the α-Keggin [HPW11.5 VI Cu0.5 II O40]4 − anion. The cooperativity of intermolecular π −π stacking, C─H… π interactions and C─H… O hydrogen bonds link the ions together to form a three-dimensional chiral structure. The luminescent properties of the title complex in the solid state were investigated.