Chiral Polarization Research Articles

Arbitrary Polarization Syntheses Based on Spin‐Momentum Locking in Spoof Surface Plasmon Polaritons

AbstractSpin‐momentum locking is universal and an inherent property of evanescent electromagnetic (EM) waves, which transfers the spinning or handedness of electromagnetic waves onto their propagation direction. This motivates an approach to investigate the polarization‐controlled directional transmission or emission. Here, the spin‐momentum locking is demonstrated in spoof surface plasmon polariton (SSPP) waveguides, and momentum‐controlled radiation is further realized in SSPP‐patch antennas. The study shows that the circular polarization of the SSPP‐patch antennas originates from the spin‐momentum locking in the SSPP waveguides and hence is determined by the propagation direction of the SSPP modes. Two examples are presented to achieve ±45° dual‐polarizations and vertical/horizontal dual‐polarizations by combining the SSPP‐patch antenna with hybrid couplers. Finally, a straightforward method is proposed for synthesizing the polarization emitted by the SSPP‐patch antenna, allowing access to arbitrary polarization states on the Poincare sphere. The SSPP‐patch antenna is polarization responsive, shedding light on chiral sensors, Stokes polarimetry, and polarization measurement. Hence, the spin‐momentum locking and the related momentum‐controlled radiations provide additional freedom to regulate the EM waves by engineering the helicity in the SSPP waveguide.

Real-time monitoring of polarization state deviations with dielectric metasurfaces

We propose and experimentally demonstrate a dielectric metasurface that allows monitoring of polarization deviations from an arbitrary elliptical input anchor state simply by tracking in real-time the output ratio between the powers of horizontal and vertical components after the metasurface. Importantly, this ratio can be enhanced corresponding to increased responsivity. Such nontrivial functionality is achieved by designing binary metasurfaces that realize tailored nonunitary and chiral polarization transformation. We experimentally demonstrate the operation at telecommunication wavelengths with enhanced responsivity up to 25 for various anchor states, including the strongly elliptical and circular. We also achieve the uncertainty of deviation measurement that is significantly better than the fundamental limit for nonchiral metasurfaces.

The Chiral Spin-Orbitronics of a Helimagnet–Normal Metal Heterojunction

A theory of spin and charge transport in bounded metallic magnets has been constructed, which takes into account the effects of spin-orbit scattering of conduction electrons by crystal lattice defects. The theory can be used to describe the spin Hall effect and the anomalous Hall effect and can serve as a basis for describing the phenomena of spin-orbitronics. Phenomenological boundary conditions for the charge and spin fluxes at the interface between two different metals have been formulated, on the basis of which the injec-tion of a pure spin current into a helimagnet, which arises in a normal metal as a manifestation of the spin Hall effect, is described. The existence of an “effect of chiral polarization of a pure spin current” is predicted, which consists in the appearance in a helimagnet of a longitudinally polarized pure spin current and a longi-tudinal component of the nonequilibrium electron magnetization, depending on the chirality of the helimag-net helix, upon injection of a transversely polarized spin current from a normal metal.

The Chiral Spin-Orbitronics of a Helimagnet–Normal Metal Heterojunction

A theory of spin and charge transport in bounded metallic magnets has been constructed, which takes into account the effects of spin-orbit scattering of conduction electrons by crystal lattice defects. The theory can be used to describe the spin Hall effect and the anomalous Hall effect and can serve as a basis for describing the phenomena of spin-orbitronics. Phenomenological boundary conditions for the charge and spin fluxes at the interface between two different metals have been formulated, on the basis of which the injection of a pure spin current into a helimagnet, which arises in a normal metal as a manifestation of the spin Hall effect, is described. The existence of an “effect of chiral polarization of a pure spin current” is predicted, which consists in the appearance in a helimagnet of a longitudinally polarized pure spin current and a longitudinal component of the nonequilibrium electron magnetization, depending on the chirality of the helimagnet helix, upon injection of a transversely polarized spin current from a normal metal.

Chiral selectivity vs. noise in spontaneous mirror symmetry breaking.

Mirror symmetry breaking bifurcations, that occur in nonlinear chemical systems leading to final chiral states with very large enantiomeric excess, can be exploited as an efficient chiral signal selector for even the smallest chiral polarizations. This effect of the chiral polarization requires the system's capacity for overcoming thermal noise, which is manifested as fluctuating reaction rate constants. Therefore, we investigate the chiral selectivity across a range of tiny parity-violating energy differences (PVED) in the presence of inevitable non-equilibrium temperature fluctuations. We use a stochastic differential equation simulation methodology (Ito process) that serves as a valuable tool in open systems for identifying the thresholds at which the chiral force induces chiral selectivity in the presence of non-equilibrium temperature fluctuations. This approach enables us to include and analyze chiral selectivity in the presence of other types of fluctuations, such as perturbations in the rate of fluid flow into and out of the reactor and in the clamped input concentrations. These concepts may be of practical interest (i.e., spontaneous deracemizations) but are also useful for a better understanding of the general principles governing the emergence of biological homochirality.

Spontaneous electric-polarization topology in confined ferroelectric nematics

Topological textures have fascinated people in different areas of physics and technologies. However, the observations are limited in magnetic and solid-state ferroelectric systems. Ferroelectric nematic is the first liquid-state ferroelectric that would carry many possibilities of spatially-distributed polarization fields. Contrary to traditional magnetic or crystalline systems, anisotropic liquid crystal interactions can compete with the polarization counterparts, thereby setting a challenge in understating their interplays and the resultant topologies. Here, we discover chiral polarization meron-like structures, which appear during the emergence and growth of quasi-2D ferroelectric nematic domains. The chirality can emerge spontaneously in polar textures and can be additionally biased by introducing chiral dopants. Such micrometre-scale polarization textures are the modified electric variants of the magnetic merons. Both experimental and an extended mean-field modelling reveal that the polarization strength plays a dedicated role in determining polarization topology, providing a guide for exploring diverse polar textures in strongly-polarized liquid crystals.

Wide-angle chiral polarization converter for reflection and transmission modes

Metamaterials provide high degrees of freedom for the design and manipulation of electromagnetic (EM) waves such as polarization conversion due to their unique controllable capabilities. In this paper, we propose a tunable wide-angle chiral metamaterial incorporating with vanadium dioxide (VO2), which can realize different operating modes and polarization conversions. When working in reflection mode, it can achieve circular polarization conversion at 3.35 THz and 3.07 THz for two different incident directions, the corresponding polarization conversion rate (PCR) can reach 93.5% and 97.1%, respectively. When operating in transmission mode, the incident x (y)-polarized waves can be converted to the orthogonal counterparts in the range of 2.24–2.88 THz, the asymmetric transmission (AT) parameter is over 0.6. Moreover, the good PCR and large AT effect can still be maintained in wide angle range. The proposed structure has potential application prospects in controllable switch, isolation device, communication system and so on.

Broadband Graphene-Based Electro-Optic Chiral Polarization Conversion for Terahertz Pulse Shaping

Terahertz (THz) radiation is ideally suited for noninvasive testing and short-distance data transmission. Actively controlling the polarization of THz waves is highly desirable in measurement systems. Although significant developments of THz active devices has been achieved through introducing the electromagnetic resonance structure (e.g., metamaterials), the bandwidth is limited. Here, we propose a graphene-based electrically reconfigurable polarization conversion across a broadband THz region (0.3 to 0.9 THz) for controlling the chiral polarization of terahertz pulse. By electrically controlling the graphene conductivity, we can switch the device reflection in-between total internal reflection and metal mirror reflection to realize a frequency-independent phase change, which enables a tunable waveplate with a high dynamic range for manipulating the polarization of THz waves. Because of the frequency-independent modulation property, we achieved tunable chiral polarization THz waveforms in the time domain for the first time, from right-handed to left-handed polarization. This work opens up a new mechanism for designing novel THz modulators for THz circular dichroism.

Properties of strange quark matter under strong rotation

We investigate the rotating quark matter in the three-flavor Nambu--Jona-Lasinio (NJL) model. The chiral condensation, spin polarization, and number susceptibility of the light and strange quarks are carefully studied at finite temperatures without or with finite chemical potential in this model. We find that the rotation suppresses the chiral condensation and enhances the first-order quark spin polarization, however for the second-order quark spin polarization and quark number susceptibility the effect is complicated and interesting. When extending to the situation with finite chemical potential, we find the angular velocity also plays a crucial role, at small angular velocity the chemical potential enhances the susceptibility, however in the middle region of angular velocity the effect of the chemical potential is suppressed by the angular velocity and susceptibility can be changed considerably, it can be observed that at very low temperature in the presence of quark chemical potential the quark number susceptibility has two maxima with increasing angular velocity. Furthermore, it is found that at sufficiently large angular velocity the contributions played by the light quark and the strange quark to these phenomena are almost equal. We also discuss the chiral phase transition of rotating quark matter in the three-flavor NJL model. We expect these studies to be used to understand the chiral symmetry breaking and restoration as well as probe the QCD phase transition.

Crystal Structure of Chiral Drug Prenalterol and Its Precursor Prone to Spontaneous Resolution

Due to the chiral uniformity of proteins and carbohydrates, the basic building blocks of living matter, the mirror symmetry characteristics of drugs are of exceptional importance for medicinal chemistry. In this work, we present a new synthesis of the mono-enantiomeric chiral drug prenalterol 1 based on the symmetry-breaking phenomenon, namely, the spontaneous resolution of 4-hydroxyphenyl glycerol ether 2. The single crystal X-ray diffraction method was used to investigate both rac- and (S)-1 as well as (R)-2. A feature of the main crystal-forming supramolecular motif (SMM) for diol 2 is the participation of three different molecules representing different types of hydroxyl groups in the formation of its repeating unit. The type of prenalterol SMM, as in the case of the related drugs propranolol 3 and pindolol 4, appears to be a chirality driven property, and is dictated by the enantiomeric composition of the crystals. In single-enantiomeric forms, infinite one-dimensional chains are realized, organized around helical axes, while in racemates, zero-dimensional cycles are realized, organized around inversion symmetry elements. The results obtained again demonstrate the influence of the chiral polarization of a substance not only on the general (selection of a space group), but also on particular characteristics of matter crystal organization, namely selection of a specific SMM.

Simultaneous Realization of Dynamic and Hybrid Multiplexed Holography via Light‐Activated Chiral Superstructures (Laser Photonics Rev. 16(5)/2022)

Dynamic Multiplexed Holography In article number 2200011, Peng Chen, Wei Hu, Yan-Qing Lu, and colleagues from Nanjing University report a new strategy for simultaneous realization of dynamic and high-dimensional multiplexed holography. Via light-directed liquid-crystalline chiral superstructures, a photo-active, bidirectional, polarization- and time-dependent hologram is demonstrated. This novel methodology integrates diverse multiplexing schemes into a single device, facilitating advanced display, security and communication.

Stability of chiral polarization vortex in strained ferroelectric superlattices

As a geometric property that cannot overlap with its mirror image, chirality is becoming more and more common in electronic structures. The recent discovery of chiral topological polar structures in artificial ferroelectric superlattices is not only of scientific importance but also holds promise for application in tunable frequency oscillators. Although the tubular chiral polarization vortex has been observed in PbTiO3/SrTiO3 superlattices, the conditions for its stability remain elusive. Here, we construct a temperature-strain phase diagram for the (PbTiO3)10/(SrTiO3)10 superlattices by using phase field simulation in which four domain states exist at different temperatures and misfit strains. It is found that the chiral polarization vortex appears only in a small range of misfit strain, elucidating the absence of chirality in most ferroelectric superlattices. The chiral polarization vortex is an intermediate state between the ordinary achiral polarization vortex and the mixed domain structure. In addition, by changing strain or temperature, chiral vortices can be reversibly transformed into achiral vortices, demonstrating its tunability. The present work provides theoretical guidance for creating the chiral vortex in ferroelectric superlattices.

Geometry and topology tango in ordered and amorphous chiral matter

Systems as diverse as mechanical structures and photonic metamaterials enjoy a common geometrical feature: a sublattice or chiral symmetry first introduced to characterize electronic insulators. We show how a real-space observable, the chiral polarization, distinguishes chiral insulators from one another and resolve long-standing ambiguities in the very concept of their bulk-boundary correspondence. We use it to lay out generic geometrical rules to engineer topologically distinct phases, and design zero-energy topological boundary modes in both crystalline and amorphous metamaterials.

Anti-parity-time symmetry enabled on-chip chiral polarizer

Encircling an exceptional point (EP) in a parity-time (PT) symmetric system has shown great potential for chiral optical devices, such as chiral mode switching for symmetric and antisymmetric modes. However, to our best knowledge, chiral switching for polarization states has never been reported, although chiral polarization manipulation has significant applications in imaging, sensing, communication, etc. Here, inspired by the anti-PT symmetry, we demonstrate, for the first time to our best knowledge, an on-chip chiral polarizer by constructing a polarization-coupled anti-PT symmetric system. The transmission axes of the chiral polarizer are different for forward and backward propagation. A polarization extinction ratio of over 10 dB is achieved for both propagating directions. Moreover, a telecommunication experiment is performed to demonstrate the potential applications in polarization encoding signals. It provides a novel functionality for encircling-an-EP parametric evolution and offers a new approach for on-chip chiral polarization manipulation.

Interaction of Amyloid-β-(1-42) Peptide and Its Aggregates with Lipid/Water Interfaces Probed by Vibrational Sum-Frequency Generation Spectroscopy.

In this study, we use surface-sensitive vibrational sum-frequency generation (VSFG) spectroscopy to investigate the interaction between model lipid monolayers and Aβ(1-42) in its monomeric and aggregated states. Combining VSFG with atomic force microscopy (AFM) and thioflavin T (ThT) fluorescence measurements, we found that only small aggregates with probably a β-hairpin-like structure adsorbed to the zwitterionic lipid monolayer (DOPC). In contrast, larger aggregates with an extended β-sheet structure adsorbed to a negatively charged lipid monolayer (DOPG). The adsorption of small, initially formed aggregates strongly destabilized both monolayers, but only the DOPC monolayer was completely disrupted. We showed that the intensity of the amide-II' band in achiral (SSP) and chiral (SPP) polarization combinations increased in time when Aβ(1-42) aggregates accumulated at the DOPG monolayer. Nevertheless, almost no adsorption of preformed mature fibrils to DOPG monolayers was detected. By performing spectral VSFG calculations, we revealed a clear correlation between the amide-II' signal and the degree of amyloid aggregates (e.g., oligomers or (proto)fibrils) of various Aβ(1-42) structures. The calculations showed that only structures with a significant amyloid β-sheet content have a strong amide-II' intensity, in line with previous Raman studies. The combination of the presented results substantiates the amide-II(') band as a legitimate amyloid marker.

Chiral polarization textures induced by the flexoelectric effect in ferroelectric nanocylinders

Polar chiral structures have recently attracted much interest within the scientific community, as they pave the way towards innovative device concepts similar to the developments achieved in nanomagnetism. Despite the growing interest, many fundamental questions related to the mechanisms controlling the appearance and stability of ferroelectric topological structures remain open. In this context, ferroelectric nanoparticles provide a flexible playground for such investigations. Here, we present a theoretical study of ferroelectric polar textures in a cylindrical core-shell nanoparticle. The calculations reveal a chiral polarization structure containing two oppositely oriented diffuse axial domains located near the cylinder ends, separated by a region with a zero-axial polarization. We name this polarization configuration "flexon" to underline the flexoelectric nature of its axial polarization. Analytical calculations and numerical simulation results show that the flexon's chirality can be switched by reversing the sign of the flexoelectric coefficient. Furthermore, the anisotropy of the flexoelectric coupling is found to critically influence the polarization texture and domain morphology. The flexon rounded shape, combined with its distinct chiral properties and the localization nature near the surface, are reminiscent of Chiral Bobber structures in magnetism. In the azimuthal plane, the flexon displays the polarization state of a vortex with an axially polarized core region, i.e., a meron. The flexoelectric effect, which couples the electric polarization and elastic strain gradients, plays a determining role in the stabilization of these chiral states. We discuss similarities between this interaction and the recently predicted ferroelectric Dyzaloshinskii-Moriya interaction leading to chiral polarization states.

Terahertz circular dichroism sensing of living cancer cells based on microstructure sensor

Terahertz (THz) waves have the advantages of being noninvasive and nonionizing because of their low radiation energy, so they have potential applications in the biomedical field, but thus far, those have been limited by the strong absorption in water and low detection sensitivity. Herein, we propose a reflective THz time-domain circular dichroism (CD) sensing system and a silicon subwavelength grating as the microstructure sensor to generate and detect the THz chiral polarization states, to realize quantitative detection of living cell numbers and qualitative identification of cell kinds in a liquid environment. Three kinds of hepatoma cell proliferation and inhibition with different concentrations of aspirin were measured by this sensing method, and the experimental results show that the sensitivities for CD resonance intensity and frequency shift can reach 3.44 dB mL/106 cells and 5.88 GHz mL/106 cells, respectively, and the minimum detection concentration is in the order of 104 cells/mL for THz detection in a liquid environment for the first time. This new THz sensing system and sensing method are expected to become a broadband, label-free, noncontact, real-time detection technology that can be used for quantitative detection and qualitative identification of cells or other active biochemical materials.

Up‐And‐Coming Advances in Optical and Microwave Nonreciprocity: From Classical to Quantum Realm

Reciprocity is a fundamental physical principle that roots in the time‐reversal symmetry of physical laws. It allows making predictions on any arbitrary complex system's response and operation and hence simplifies the analysis. However, there are many practical situations in which it is advantageous to break reciprocity, e.g., isolators preventing wave scattering back to lasers and generators, full‐duplex systems for multiplexing transmission and receiving in the same channel, nonreciprocal cavity excitation, and protection of fragile states of superconductor quantum computers from thermal noise. The most widespread approach to time‐reversal symmetry breaking and nonreciprocity based on magnetic field biasing suffers from bulkiness, cost ineffectiveness, and loss, motivating researchers and engineers to search for more practical approaches. Herein, the up‐and‐coming advances in optical nonreciprocity, including new materials (Weyl semimetals, topological insulators, metasurfaces), active structures, time‐modulation, parity‐time (PT)‐symmetry breaking, nonlinearity combined with a structural asymmetry, quantum nonlinearity, unidirectional gain and loss, chiral quantum states and valley polarization are overviewed. A general description of nonreciprocal systems is provided and the pros and cons of the mentioned approaches to nonreciprocity are discussed.

The interaction of chondroitin sulfate with a lipid monolayer observed by using nonlinear vibrational spectroscopy.

The first vibrational sum-frequency generation (VSFG) spectra of chondroitin sulfate (CS) interacting with dipalmitoyl phosphatidylcholine (DPPC) at air–liquid interface are reported here, collected at a laser repetition rate of 100 kHz. By studying the VSFG spectra in the regions of 1050–1450 cm−1, 2750–3180 cm−1, and 3200–3825 cm−1, it was concluded that in the presence of Ca2+ ions, the head groups together with the head-group-bound water molecules in the DPPC monolayer are strongly influenced by the interaction with CS, while the organization of the phospholipid tails remains mostly unchanged. The interactions were observed at a CS concentration below 200 nM, which exemplifies the potential of VSFG in studying biomolecular interactions at low physiological concentrations. The VSFG spectra recorded in the O–H stretching region at chiral polarization combination imply that CS molecules are organized into ordered macromolecular superstructures with a chiral secondary structure.

An efficient chiral polarization rotator with asymmetric transmission for large incidence angles

A linear polarization converting chiral metasurface with asymmetric transmission is designed, analyzed, and characterized experimentally for operation in the Ku band of the microwave frequency regime. The proposed structure consists of two metasurface layers of asymmetric square-shaped unit cells with quarter moon polygon split-ring resonators. By breaking certain symmetries of the chiral structure, the proposed structure achieves efficient asymmetric transmission with the asymmetric transmission parameter of more than 80% and a polarization conversion ratio of more than 90% for 13.87–16.04 GHz. Moreover, the proposed structure gives a stable response to the variations in the incidence angle up to 45° both for transverse-electric and transverse-magnetic polarizations. The high efficiency for both asymmetric transmission and polarization conversion, wide bandwidth, and angular stability qualify the proposed design for numerous microwave applications.