Opposite Helicity Research Articles

Recursion in the classical limit and the neutron-star Compton amplitude

We study the compatibility of recursive techniques with the classical limit of scattering amplitudes through the construction of the classical Compton amplitude for general spinning compact objects. This is done using BCFW recursion on three-point amplitudes expressed in terms of the classical spin vector and tensor, and expanded to next-to-leading-order in ћ by using the heavy on-shell spinors. Matching to the result of classical computations, we find that lower-point quantum contributions are, in general, required for the recursive construction of classical, spinning, higher-point amplitudes with massive propagators. We are thus led to conclude that BCFW recursion and the classical limit do not commute. In possession of the classical Compton amplitude, we remove non-localities to all orders in spin for opposite graviton helicities, and to fifth order in the same-helicity case. Finally, all possible on-shell contact terms potentially relevant to black-hole scattering at the second post-Minkowskian order are enumerated and written explicitly.

A chiral inverse Faraday effect mediated by an inversely designed plasmonic antenna.

The inverse Faraday effect is a magneto-optical process allowing the magnetization of matter by an optical excitation carrying a non-zero spin of light. This phenomenon was considered until now as symmetric; right or left circular polarizations generate magnetic fields oriented in the direction of light propagation or in the counter-propagating direction. Here, we demonstrate that by manipulating the spin density of light in a plasmonic nanostructure, we generate a chiral inverse Faraday effect, creating a strong magnetic field of 500 mT only for one helicity of the light, the opposite helicity producing this effect only for the mirror structure. This new optical concept opens the way to the generation of magnetic fields with unpolarized light, finding application in the ultrafast manipulation of magnetic domains and processes, such as spin precession, spin currents and waves, magnetic skyrmion or magnetic circular dichroism, with direct applications in data storage and data processing technologies.

Helical Long-Period Fiber Grating-Based OAM Interferometer and Its Application to Fiber Sensing

Orbital-angular-momentum (OAM) beams-based interferometers have recently been attracted significant interest and found various applications in the field of optical precision measurement. Whereas all-fiber OAM interferometers featured with the superior characteristics of the compact size, low cost, extremely-low insertion-loss, and the inherent compatibility with other fiber devices, have less been studied and especially demonstrated in experiment. In this study, we proposed and experimentally demonstrated an all-fiber OAM beams-based interferometer, where the two conjugated OAM beams generated by helical long-period fiber gratings (HLPGs) but with opposite helicities, were particularly utilized as the tested and referenced beams, respectively. The resulted interferograms are of the polarization independence, robust, and particularly suitable for phase-demodulation in azimuthal angle domain. As application examples of the proposed all-fiber OAM beams-based interferometer, changes in temperature ranging from 30 °C to 60 °C and changes in the strain ranging from 0 to 100 μϵ were measured, respectively. The obtained maximum sensitivity in temperature and strain are 26.585 rad/°C and 2.130 rad/μϵ, respectively. The accuracies for temperature and strain measurements are estimated to be 0.0016 °C and 0.0195 μϵ, respectively, which are about 2–3 order higher than those obtained from the conventional optical fiber-based sensors. It is believed that the proposed all-fiber OAM beams-based interferometer would find potential applications to ultra-high precision and sensing measurements.

Stereospecific Synthesis of Enantiopure [6]Helicene Containing a Seven-Membered Ring and [7]Helicene by Acid-Promoted Stepwise Alkyne Annulations of Doubly Axial-Chiral Precursors.

Enantiopure [6]helicene containing an embedded seven-membered ring and carbo[7]helicene (>99 % ee) with opposite helicity were simultaneously and quantitatively (>99 %) synthesized with a perfect stereospecificity through stepwise acid-promoted intramolecular alkyne annulations of doubly axial-chiral cyclization precursors. The helical handedness of the [6]- and [7]helicenes was fully stereocontrolled by the doubly axial chirality of the precursors as a result of complete axial-to-helical chirality transfer. The cyclizations proceeded in a stepwise manner; the first six-membered ring formation was followed by the kinetically controlled seven- or six-membered ring formation with or without helix-inversion of a [4]helicene intermediate generated during the first cyclization step, thus quantitatively producing enantiopure circularly polarized luminescent [6]- and [7]helicenes with opposite helicity.

Stereospecific Synthesis of Enantiopure [6]Helicene Containing a Seven‐Membered Ring and [7]Helicene by Acid‐Promoted Stepwise Alkyne Annulations of Doubly Axial‐Chiral Precursors**

AbstractEnantiopure [6]helicene containing an embedded seven‐membered ring and carbo[7]helicene (>99 % ee) with opposite helicity were simultaneously and quantitatively (>99 %) synthesized with a perfect stereospecificity through stepwise acid‐promoted intramolecular alkyne annulations of doubly axial‐chiral cyclization precursors. The helical handedness of the [6]‐ and [7]helicenes was fully stereocontrolled by the doubly axial chirality of the precursors as a result of complete axial‐to‐helical chirality transfer. The cyclizations proceeded in a stepwise manner; the first six‐membered ring formation was followed by the kinetically controlled seven‐ or six‐membered ring formation with or without helix‐inversion of a [4]helicene intermediate generated during the first cyclization step, thus quantitatively producing enantiopure circularly polarized luminescent [6]‐ and [7]helicenes with opposite helicity.

Preferential molecular recognition of heterochiral guests within a cyclophane receptor

The discrimination of enantiomers by natural receptors is a well-established phenomenon. In contrast the number of synthetic receptors with the capability for enantioselective molecular recognition of chiral substrates is scarce and for chiral cyclophanes indicative for a preferential binding of homochiral guests. Here we introduce a cyclophane composed of two homochiral core-twisted perylene bisimide (PBI) units connected by p-xylylene spacers and demonstrate its preference for the complexation of [5]helicene of opposite helicity compared to the PBI units of the host. The pronounced enantio-differentiation of this molecular receptor for heterochiral guests can be utilized for the enrichment of the P-PBI-M-helicene-P-PBI epimeric bimolecular complex. Our experimental results are supported by DFT calculations, which reveal that the sterically demanding bay substituents attached to the PBI chromophores disturb the helical shape match of the perylene core and homochiral substrates and thereby enforce the formation of syndiotactic host-guest complex structures. Hence, the most efficient substrate binding is observed for those aromatic guests, e. g. perylene, [4]helicene, phenanthrene and biphenyl, that can easily adapt in non-planar axially chiral conformations due to their inherent conformational flexibility. In all cases the induced chirality for the guest is opposed to those of the embedding PBI units, leading to heterochiral host-guest structures.

Circularly Polarized Lasing from a Microcavity Filled with Achiral Single‐Crystalline Microribbons

AbstractOrganic circularly polarized (CP) lasers have received increasing attention due to their future photoelectric applications. Here, we demonstrate a CP laser from a pure organic crystal‐filled microcavity without any chiral molecules or chiral structures. Benefited from the giant anisotropy and excellent laser gain of organic crystals, optical Rashba‐Dresselhaus spin‐orbit coupling effect can be induced and is conductive to the CP laser in such microcavities. The maximum dissymmetry factor of the CP lasing with opposite helicities reachs 1.2. Our strategy may provide a new idea for the design of CP lasers towards future 3D laser displays, information storage and other fields.

Circularly Polarized Lasing from a Microcavity Filled with Achiral Single-Crystalline Microribbons.

Organic circularly polarized (CP) lasers have received increasing attention due to their future photoelectric applications. Here, we demonstrate a CP laser from a pure organic crystal-filled microcavity without any chiral molecules or chiral structures. Benefited from the giant anisotropy and excellent laser gain of organic crystals, optical Rashba-Dresselhaus spin-orbit coupling effect can be induced and is conductive to the CP laser in such microcavities. The maximum dissymmetry factor of the CP lasing with opposite helicities reachs 1.2. Our strategy may provide a new idea for the design of CP lasers towards future 3D laser displays, information storage and other fields.

A skyrmion helicity-based multistate memory in synthetic antiferromagnets

Skyrmions in synthetic antiferromagnets (SAFs) are famous for being immune to the skyrmion Hall effect and hold the advantages of significantly higher speed for motion and smaller size than ferromagnetic systems. Therefore, skyrmions in SAFs are promising in spintronic devices. Here, we investigated the formation and in-plane-current-driven motion of bilayer skyrmions in the absence of Dzyaloshinskii–Moriya interaction by using micromagnetic simulations. Then, we studied the spacing variation between consecutive skyrmionic bits on the antiferromagnetic coupled nanotrack; it is found that there is an equilibrium distance between two Bloch skyrmions with opposite helicities. We also propose a reasonable method to distinguish skyrmions with opposite helicities. Finally, we displayed that the SAF skyrmion could pass through impurities due to topological protection. Based on these results, we designed the skyrmion helicity-based multistate memory devices in the SAF system, which have the advantages of high density and energy efficiency.

Wide field of view chiral imaging with a liquid crystal planar lens enabled by digitalized nanogratings.

To compensate for the inability for polarization imaging by conventional methods, metasurface optics with compactness and multi-function emerge as an approach to provide images with different linear and circular polarizations. Here, we propose a liquid crystal (LC) geometric phase-based chiral imaging lens (CIL) that simultaneously forms images of objects with opposite helicity. The CIL (Diameter 2.3 cm) was optimized by a spatial multiplexing algorithm and realized using the digital holography technique, where the LC domains were regulated by pixelated nanogratings with varied orientation. We investigated the potential of the patterning technique toward high order LC alignment by balancing the periodicity and depth of the nanogratings. The CIL exhibited a wide field of view of ±20°, which is attributed to the self- assembling effects of LC molecules. The compactness, lightness, and ability to produce chiral images of the LC CIL even at large angles have significant potential for practical polarization imaging.

Modulating the Macroscopic Helicity of Poly(m‐phenylenediamine) by Achiral Monomer Copolymerization

AbstractDesigning artificial systems to mimic chiral superstructures and exploring how achiral molecules precisely modulate their chirality is crucial to understand the origin of homochirality in nature. Herein, the tunability nature of supramolecular chirality is subtly applied to fabricate robust chiral covalent polymers with controlled macroscopic helicity. When using conventional supramolecular transcription methods to prepare chiral poly(m‐phenylenediamine), simply introducing various small amounts of achiral diaminopyridines (DAPs) to copolymerize with m‐phenylenediamine (MPD) enables the resulting chiral copolymers with adjustable helical configurations and chiroptical activities in an enantiopure template system. The strong hydrogen bonds between DAPs and the template molecules ((S)/(R)‐PhgC16) proved to be the driving force for guiding the chiral polymerization mode of MPD. Impressively, the exquisite self‐sorting phenomenon is observed by tuning the stoichiometric ratio of DAP and (R)‐PhgC16, where the as‐prepared copolymers with opposite helicity can exist simultaneously to form a double network structure and their chiroptical activity can be well regulated. In addition, based on such a copolymerization strategy, a conceptual library of helical functional copolymers is built with editable polymer types including conducting polymers and designable amine‐aldehyde condensation‐based polymers. This copolymerization‐mediated synthetic strategy may facilitate the development of chiral polymers with controlled morphologies and dynamic compositions.

Spatiotemporal segregation of chiral supramolecular polymers

•Chirality switching in out-of-equilibrium supramolecular systems •Spatiotemporally controlled formation of chirally assorted supramolecular polymers •Audible sound-assisted segregation of chiral and achiral supramolecular polymers •Audible sound-assisted segregation of supramolecular polymers of opposite helicity Programmable spatiotemporal control over the formation of functional supramolecular polymers, which leads to the formation of different morphological forms in solution, is one of the long-standing issues in chemistry. The situation is even more complex especially when dealing with a mixture of species in multicomponent self-assemblies. One way to achieve this goal is by controlling the spatiotemporal distribution of the molecular components in solution, which control the overall aggregation process. Herein, we report the spatiotemporal segregation of different redox-responsive supramolecular assemblies inside spatiotemporal domains generated within the same solution under out-of-equilibrium conditions by using audible sound. Using this approach, we can spatiotemporally control the formation of at least two types of assemblies, which are either both achiral or one of them is chiral, or both are chiral but with opposite helicity. This strategy may provide advanced control over solution-state synthesis of supramolecular polymers, which exhibit morphology-dependent functions. Programmable spatiotemporal control over the formation of functional supramolecular polymers, which leads to the formation of different morphological forms in solution, is one of the long-standing issues in chemistry. The situation is even more complex especially when dealing with a mixture of species in multicomponent self-assemblies. One way to achieve this goal is by controlling the spatiotemporal distribution of the molecular components in solution, which control the overall aggregation process. Herein, we report the spatiotemporal segregation of different redox-responsive supramolecular assemblies inside spatiotemporal domains generated within the same solution under out-of-equilibrium conditions by using audible sound. Using this approach, we can spatiotemporally control the formation of at least two types of assemblies, which are either both achiral or one of them is chiral, or both are chiral but with opposite helicity. This strategy may provide advanced control over solution-state synthesis of supramolecular polymers, which exhibit morphology-dependent functions.

Helicity dependent photoresistance measurement vs. beam-shift thermal gradient

Optical detection techniques are among the most powerful methods used to characterize spintronic phenomena. The spin orientation can affect the light polarization, which, by the reciprocal mechanism, can modify the spin density. Numerous recent experiments, report local changes in the spin density induced by a circularly polarized focused laser beam. These effects are typically probed electrically, by detecting the variations of the photoresistance or photocurrent associated to the reversal of the light helicity. Here we show that in general, when the light helicity is modified, the beam profile is slightly altered, and the barycenter of the laser spot is displaced. Consequently, the temperature gradients produced by the laser heating will be modulated, producing thermo-electric signals that alternate in phase with the light polarization. These unintended signals, having no connection with the electron spin, appear under the same experimental conditions and can be easily misinterpreted. We show how this contribution can be experimentally assessed and removed from the measured data. We find that even when the beam profile is optimized, this effect is large, and completely overshadows the spin related signals in all the materials and experimental conditions that we have tested.

Kinetic Co-assembly Pathway Induced Chirality Inversion Along with Morphology Transition.

Kinetic co-assembly pathway induced chirality inversion along with morphology transition is of importance to understand biological processes, but still remains a challenge to realize in artificial systems. Herein, helical nanofibers consisting of phenylalanine-based enantiomers (L/DPF) successfully transform into kinetically trapped architectures with opposite helicity through a kinetic co-assembly pathway. By contrast, the co-assemblies obtained by a thermodynamic pathway exhibit non-helical structures. The formation sequence of non-covalent interactions plays a crucial role in structural chirality of co-assemblies. For the kinetic pathway, the hydrogen bonding between D/LPF and naphthylamide derivatives forms before π-π stacking to facilitate the formation of helical structures with inverse handedness. This study may provide an approach to explore chirality inversion accompanied by morphology transition by manipulating the kinetic co-assembly pathway.

Kinetic Co‐assembly Pathway Induced Chirality Inversion Along with Morphology Transition

AbstractKinetic co‐assembly pathway induced chirality inversion along with morphology transition is of importance to understand biological processes, but still remains a challenge to realize in artificial systems. Herein, helical nanofibers consisting of phenylalanine‐based enantiomers (L/DPF) successfully transform into kinetically trapped architectures with opposite helicity through a kinetic co‐assembly pathway. By contrast, the co‐assemblies obtained by a thermodynamic pathway exhibit non‐helical structures. The formation sequence of non‐covalent interactions plays a crucial role in structural chirality of co‐assemblies. For the kinetic pathway, the hydrogen bonding between D/LPF and naphthylamide derivatives forms before π‐π stacking to facilitate the formation of helical structures with inverse handedness. This study may provide an approach to explore chirality inversion accompanied by morphology transition by manipulating the kinetic co‐assembly pathway.

High harmonic generation by co-rotating bi-circular laser fields interaction with relativistic plasmas

We present an investigation of high harmonic generation (HHG) from relativistic plasmas driven by two-color co-rotating circularly polarized (CP) laser fields at various frequency ratios ω2/ω1. The theoretical analysis and the particle-in-cell simulation results reveal that when ω2/ω1≥4, CP harmonics with opposite helicities can appear simultaneously due to the relativistic mirror effect and the related conservation laws. Meanwhile, the harmonic spectra features (including the HHG efficiency, the allowed harmonic orders, and their polarization states) can be tuned through adjusting the frequency and intensity ratio of the two driving field components. This finding might be helpful for a consummate understanding of the bi-circular HHG technique.

Polarized photoelectrons from converging vector waves

This paper investigates the spin characteristics of photoelectrons when hydrogen-like ions are centro-symmetrically irradiated with converging vector waves—a non-paraxial form of structured light. For a photon with given total angular momentum and third component thereof, photoelectrons with both helicities are obtained—in contrast to the fixed helicities produced by left- or right-circularly polarized light. The angular distribution of photoelectrons is broadly tunable through the radiation mode numbers, and opposite helicities can be extracted in synchronism.

Magnetic Skyrmions with Unconventional Helicity Polarization in a Van Der Waals Ferromagnet.

Skyrmion helicity, which defines the spin swirling direction, is a fundamental parameter that may be utilized to encode data bits in future memory devices. Generally, in centrosymmetric ferromagnets, dipole skyrmions with helicity of -π/2 and π/2 are degenerate in energy, leading to equal populations of both helicities. On the other hand, in chiral materials where the Dzyaloshinskii-Moriya interaction (DMI) prevails and the dipolar interaction is negligible, only a preferred helicity is selected by the type of DMI. However, whether there is a rigid boundary between these two regimes remains an open question. Herein, the observation of dipole skyrmions with unconventional helicity polarization in a van der Waals ferromagnet, Fe5- δ GeTe2 , is reported. Combining magnetometry, Lorentz transmission electron microscopy, electrical transport measurements, and micromagnetic simulations, the short-range superstructures in Fe5- δ GeTe2 resulting in a localized DMI contribution, which breaks the degeneracy of the opposite helicities and leads to the helicity polarization, is demonstrated. Therefore, the helicity feature in Fe5- δ GeTe2 is controlled by both the dipolar interaction and DMI that the former leads to Bloch-type skyrmions with helicity of ±π/2 whereas the latter breaks the helicity degeneracy. This work provides new insights into the skyrmion topology in van der Waals materials.

Spin excitation spectrum of biskyrmion in a confined nanodot

A biskyrmion, which consist of two stable Bloch skyrmions with opposite magnetic helicities has been observed in several centrosymmetric ferromagnets such as layered perovskite manganites and MnNiGa. Here, the spin excitation modes of biskyrmion in a confined nanodot were investigated by using micromagnetic simulations. An oscillation mode at the lower frequency and two mixed modes of breathing and rotation at higher frequencies are observed. In addition, the frequencies for mixed modes exhibit remarkable dependence on the change of magnetization profile. However, the in-plane orientation of biskyrmion does not shift the excitation frequencies corresponding to all eigenmodes. Our result indicates novel excitation modes which enrich the theory of eigenmodes for spin textures and offers a direct mean of detecting and characterizing biskyrmion in experiment.

Nature of helicity injection in non-erupting solar active regions

ABSTRACT Using time-sequence vector magnetic field and coronal observations from Solar Dynamics Observatory, we report the observations of the magnetic field evolution and coronal activity in four emerging active regions (ARs). The ARs emerge with leading polarity being the same as for the majority of ARs in a hemisphere of solar cycle 24. After emergence, the magnetic polarities separate each other without building a sheared polarity inversion line. In all four ARs, the magnetic fields are driven by foot point motions such that the sign of the helicity injection (dH/dt) in the first half of the evolution is changed to the opposite sign in the later part of the observation time. This successive injection of opposite helicity is also consistent with the sign of mean force–free twist parameter (αav). Further, the EUV light curves off the ARs in 94 Å and GOES X-ray flux reveal flaring activity below C-class magnitude. Importantly, the white-light coronagraph images in conjunction with the AR images in Atmospheric Imaging Assembly (AIA) 94 Å delineate the absence of associated Coronal Mass ejections (CMEs) with the studied ARs. These observations imply that the ARs with successive injection of opposite sign magnetic helicity are not favourable to twisted flux rope formation with excess coronal helicity, and therefore are unable to launch CMEs, according to recent reports. This study provides the characteristics of helicity flux evolution in the ARs referring to the conservative property of magnetic helicity and more such studies would help to quantify the eruptive capability of a given AR.