Opposite Helicity Research Articles

Hadronic rescattering to solve the helicity puzzle in B+→pp¯π+(K+) decays

We explore the contribution of hadronic final state interactions (FSI) to propose a production mechanism and interpret the puzzle on helicity angle distributions in B+→pp¯π+ and B+→pp¯K+ decays. Experimental results indicate opposite helicity angle θp distributions in those two channels with the difference presenting a remarkable linear dependence on cosθp. We assume the production mechanism is driven by B+→xym+→pp¯m+, where m=π or K, and xy represents favorable mesonic decay channels producing pp¯. We develop a model that includes a three-body final state interaction between the p,p¯, and π+ or K+ considering the dominance of elastic channels π+p and K+p¯ interactions below 2 GeV/c2. Our three-body framework with FSI explains qualitatively the observed opposite behavior of the helicity distributions and the observed linearity. Published by the American Physical Society 2024

Spheres of maximum electromagnetic chirality

The search for objects that yield maximum electromagnetic chirality in their emitted wave field has gathered significant attention in recent years. However, achieving such maximum chirality is challenging, as it typically requires complex chiral metamaterials. Here, we demonstrate that chiral spheres can yield maximum chirality in their emitted wave field. Specifically, we analytically find the spectral trajectories at which chiral spheres become optically transparent to a given helicity of the incident field, while for its opposite helicity, they behave as dual objects, i.e., on scattering, they preserve helicity. Since chiral spheres behave as dual objects at the first Kerker condition of zero backscattering, we significantly simplify this condition in terms of a Riccati-Bessel function. Our analytical findings suggest the creation of spherical building blocks for designing metasurfaces or metamaterials with maximum electromagnetic chirality properties. Published by the American Physical Society 2024

Substrate‐Induced Maximum Optical Chirality of Planar Dielectric Structures

AbstractResonant dielectric planar structures can interact selectively with light of particular helicity thus providing an attractive platform for “chiral flat optics”. The absence of mirror‐symmetry planes defines geometric chirality, and it remains the main condition for achieving strong circular dichroism. For planar optical structures such as photonic‐crystal slabs and metasurfaces, breaking the out‐of‐plane mirror symmetry is especially challenging, as it requires to fabricate meta‐atoms with a tilt, variable height, or vertically shifted positions. Although transparent substrates formally break out‐of‐plane mirror symmetries, their optical effect is typically subtle being rarely considered for enhancing optical chirality. Here it is revealed that low‐refractive‐index substrates can induce up to maximum intrinsic optical chirality in otherwise achiral metastructures so that the transparency to waves of one helicity is combined with resonant blocking of waves of the opposite helicity. This effect originates from engineering twisted photonic eigenstates of different parities. The perturbation analysis developed in terms of the resonant‐state expansion reveals how the eigenstate coupling induced by a substrate gives rise to a pair of chiral resonances of opposite handedness. The general theory is confirmed by the specific examples of light transmission in the normal and oblique directions by a rotation‐symmetric photonic‐crystal slab placed on different transparent substrates.

Hints of auroral and magnetospheric polarized radio emission from the scallop-shell star 2MASS J05082729–2101444

Scallop-shell stars, a recently discovered class of young M dwarfs, show complex optical light curves that are characterized by periodic dips as well as other features that are stable over tens to hundreds of rotation cycles. The origin of these features is not well-understood. 2MASS J05082729−2101444 is a ∼25 Myr old scallop-shell star that was identified using TESS data; it has a photometric period of 6.73 h that has been attributed to rotation. Of the ∼50 recently confirmed scallop-shell stars, it is one of the few detected at radio frequencies between 1 and 8 GHz. We observed this rare system with the upgraded Giant Meterwave Radio Telescope at 575–720 MHz, covering 88% of the photometric period in each of the two observations scheduled almost a month apart in 2023. We detected approximately millijansky emission from the target in both epochs, with a significant circular polarization fraction: |V/I|∼20 − 50%. The 3.5-minute phase-folded light curves show unique variability in circular polarization. We detected an approximately hour-long helicity reversal during both epochs, and the reversals had similar amplitudes, lengths, and (possibly) occured at similar phases. These results suggest two emission components: The first is a persistent, moderately polarized component possibly ascribable to gyro-synchrotron emission driven by centrifugal breakout events. The second is a highly polarized, short burst-like component that is likely due to an electron cyclotron maser (ECM); it is indicative of auroral emission and is potentially responsible for the helicity reversal. To explain this, we discuss the different origins of the plasma responsible for the radio emission, including the possibility that the occulting material is acting as a plasma source. Future coordinated multifrequency radio and optical observations can further constrain the underlying scenario, as well as the magnetic geometry of the system, if we assume an ECM-like auroral emission.

Low spin solutions of higher spin gravity: BPST instanton

Higher spin gravities do not have a low energy limit where higher-spin fields decouple from gravity. Nevertheless, it is possible to construct fine-tuned exact solutions that activate low-spin fields without sourcing the higher-spin fields. We show that BPST (Belavin-Polyakov-Schwartz-Tyupkin) instanton is an exact solution of Chiral Higher Spin Gravity, i.e. it is also a solution of the holographic dual of Chern-Simons matter theories. This gives an example of a low-spin solution. The instanton sources the opposite helicity spin-one field and a scalar field. We derive an Effective Field Theory that describes the coupling between an instanton and the other two fields, whose action starts with the Chalmers-Siegel action and has certain higher derivative couplings.

The characteristics of vortex modes in twisted fiber with dielectrically chiral ring core

A novel twisted ring core fiber incorporating chiral material into the ring core is proposed, which supports orbital angular momentum (OAM) modes. Results show that between chirality and twist rate there exist a cooperative effect in birefringence and a competitive effect in mode index bifurcation between OAM modes with different helicity. The cooperative effect between chirality and twist rate also breaks the degeneracy within OAM modes of the same or opposite helicity while preserving the vectorial nature of the modes. The OAM modes generated by twisted dielectrically chiral fiber are less likely to have crosstalk. The dependences of OAM modes birefringence on chirality and twist rate are investigated. Additionally, the mode effective index bifurcation as a function of wavelength is also discussed under both kind of chirality. Owing to high birefringence, good refractive index bifurcation, we believe that this kind of fiber can find applications in new kind of OAM mode generators, OAM mode filters, optical communication, and sensing.

Giant X-Ray Circular Dichroism in a Time-Reversal Invariant Antiferromagnet.

X-ray circular dichroism, arising from the contrast in X-ray absorption between opposite photon helicities, serves as a spectroscopic tool to measure the magnetization of ferromagnetic materials and identify the handedness of chiral crystals. Antiferromagnets with crystallographic chirality typically lack X-ray magnetic circular dichroism because of time-reversal symmetry, yet exhibit weak X-ray natural circular dichroism. Here, the observation of giant natural circular dichroism in the Ni L3-edge X-ray absorption of Ni3TeO6 is reported, a polar and chiral antiferromagnet with effective time-reversal symmetry. To unravel this intriguing phenomenon, a phenomenological model is proposed that classifies the movement of photons in a chiral crystal within the same symmetry class as that of a magnetic field. The coupling of X-ray polarization with the induced magnetization yields giant X-ray natural circular dichroism, revealing typical ferromagnetic behaviors allowed by the symmetry in an antiferromagnet, i.e., the altermagnetism of Ni3TeO6. The findings provide evidence for the interplay between magnetism and crystal chirality in natural optical activity. Additionally, the first example of a new class of magnetic materials exhibiting circular dichroism is established with time-reversalsymmetry.

Skyrmion lattice in centrosymmetric magnets with local Dzyaloshinsky–Moriya interaction

It is common for the local inversion symmetry to break in crystals, even though the whole crystal has global inversion symmetry. This local inversion symmetry breaking allows for a local Dzyaloshinsky–Moriya interaction (DMI) in magnetic crystals. Here we show that the local DMI can stabilize a skyrmion as a metastable excitation or as a skyrmion crystal in equilibrium. We consider the crystal structure with layered structure as an example, where local inversion is violated in each layer but a global inversion center exists in the middle of the two layers. These skyrmions come in pairs that are related by inversion symmetry. The two skyrmions with opposite helicity in a pair form a bound state. We study the properties of a skyrmion pair in the ferromagnetic background and determine the equilibrium phase diagram, where a robust lattice of skyrmion pairs is stabilized. Our results point to a new direction to search for the skyrmion lattice in centrosymmetric magnets.

Perfect Polar Alignment of Parallel Beloamphiphile Layers: Improved Structural Design Bias Realized in Ferroelectric Crystals of the Novel "Methoxyphenyl Series of Acetophenone Azines".

An improved design is described for ferroelectric crystals and implemented with the "methoxyphenyl series" of acetophenone azines, (MeO-Ph, Y)-azines with Y=F (1), Cl (2), Br (3), or I (4). The crystal structures of these azines exhibit polar stacking of parallel beloamphiphile monolayers (PBAMs). Azines 1, 3, and 4 form true racemates whereas chloroazine 2 crystallizes as a kryptoracemate. Azines 1-4 are helical because of the N-N bond conformation. In true racemates the molecules of opposite helicity (M and P) are enantiomers A(M) and A*(P) while in kryptoracemates they are diastereomers A(M) and B*(P). The stacking mode of PBAMs is influenced by halogen bonding, with 2-4 showcasing a kink due to directional interlayer halogen bonding, whereas fluoroazine 1 demonstrates ideal polar stacking by avoiding it. Notably, (MeO-Ph, Y)-azines display a stronger bias for dipole parallel alignment, attributed to the linearity of the biphenyl moiety as compared to the phenoxy series of (PhO, Y)-azines with their non-linear Ph-O-Ph moiety. The crystals of 1-4 all feature planar biphenyls and this synthon facilitates their crystallization through potent triple T-contacts and enhances their nonlinear optical (NLO) performance by increasing conjugation length and affecting favorable chromophore conformations in the solids.

Helicity Control of Circularly Polarized Luminescence from Aromatic Conjugated Copolymers and Their Mixture Using Reversibly Photoinvertible Chiral Liquid Crystals.

We synthesized cyclic chiral compounds [(R)/(S)-D2s] by linking a photoresponsive bisbenzothienylethene (BTE) moiety with an axially chiral binaphthyl moiety. Chiral nematic liquid crystals (N*-LCs) were prepared by adding chiral compounds as dopants to host N-LCs. These N*-LCs exhibited reversible chirality inversion upon photoisomerization between the open and closed forms of the BTE moiety. Here, the mechanism underlying chirality inversion in photoresponsive N*-LCs was investigated by comparing the helical twisting powers (HTPs) of (R)-D2s with those of analogous compounds. It was found that the helical inversion of N*-LCs containing (R)-D2s is governed by a delicate balance between two types of opposite helicity, i.e., the right-handed helicity of the inherently chiral binaphthyl moiety and the left-handed helicity of the BTE moiety bearing intramolecularly induced chirality. Namely, (R)-D2s induced chirality of the BTE moiety, which is attributed to intramolecular chirality transfer from the axially chiral binaphthyl moiety to the BTE moiety. Thus, (R)-D2s are chiral compounds with double chirality consisting of an intrinsically chiral moiety and an intramolecularly induced chiral moiety. Photocontrol of the helical senses and reversible photoinversion of the N*-LCs are achieved by utilizing UV and visible light irradiation and the steric effects of the substituents at the binaphthyl rings in (R)-D2s. In addition, photocontrol of the induced circularly polarized luminescence (CPL) was achieved using the photoinvertible N*-LC. The achiral aromatic conjugated copolymers that exhibited red, green, and blue fluorescence were dissolved and mixed in the present N*-LC, and they exhibited left- and right-handed white CPL with large dissymmetry factors (|glum|) ranging from 0.2 to 1.0. The CPLs were reversibly photoswitched due to photoisomerization between the open and PSS forms of the chiral compounds through UV and visible light irradiation.

Generating attosecond pulses with controllable polarization from cyclic H32+ molecules by bichromatic circular fields

We investigate the polarization properties of harmonics from the cyclic H32+ molecular ions in tailored bichromatic counter-rotating circularly polarized (BCCP) fields by solving the time-dependent Schrödinger equation. The allowed harmonics and their helicities are associated with the symmetry compatibility of the field-target systems, and large intensity difference between adjacent harmonics with opposite helicities appears in a wide spectral range when the BCCP field is at certain rotation angles. We try to explain the intensity difference by using a recombination model based on the quantum-orbit theory and by analyzing the ionization pathways. Moreover, to synthesize attosecond pulse trains with tunable polarization, the intensity difference is manipulated by introducing a seed XUV field, and by changing the relative amplitude ratio as well as the helicity of BCCP fields.

High-efficiency plasmonic vortex generation with near-infrared bifunctional metasurfaces.

Plasmonic vortices have shown a wide range of applications in on-chip photonics due to their fascinating properties of the orbital angular momenta (OAM) and phase singularity. However, conventional devices to generate them suffer from issues of low efficiencies and limited functionalities. Here, we establish a systematic scheme to construct high-efficiency bifunctional metasurfaces that can generate two plasmonic vortices exhibiting distinct topological charges, based on a series of reflective meta-atoms exhibiting tailored reflection-phases dictated by both resonant and geometric origins. As a benchmark test, we first construct a meta-coupler with meta-atoms exhibiting geometric phases only, and experimentally demonstrate that it can generate a pre-designed plasmonic vortex at the wavelength of 1064 nm with an efficiency of 27% (56% in simulation). Next, we design/fabricate two bifunctional metasurfaces with meta-atoms integrated with both resonant and geometric phases, and experimentally demonstrate that they can generate divergent (or focused) or convergent (or defocused) plasmonic vortices with district OAM as shined by circularly polarized light with opposite helicity at 1064 nm wavelength. Our work provides an efficient platform to generate plasmonic vortices as desired, which can find many applications in on-chip photonics.

Elliptic Dichroism in the Above-Threshold Ionization of Molecules Induced by a Strong Laser Field.

Using a strong-field-approximation theory, we investigate the high-order above-threshold ionization of diatomic molecules exposed to the monochromatic and bichromatic elliptically polarized fields. We devote particular attention to the difference between the photoelectron momentum distributions obtained with fields with opposite helicity. This difference is quantified using the elliptic-dichroism parameter, which represents the normalized difference between the differential ionization rates calculated with driving fields with opposite helicity. We find that this parameter strongly depends on the molecular orientation with respect to the laser field. In addition, this dependence is different for molecules with different types of highest-occupied molecular orbital. In other words, we show that the molecular structure is imprinted onto the elliptic-dichroism parameter for both monochromatic and bichromatic driving fields. This is explained by analyzing the interferences between various partial contributions to the differential ionization rate. In this way, elliptic dichroism also serves as a tool to analyze the electron dynamics. Finally, for heteronuclear diatomic molecules, we show that the elliptic dichroism is different from zero even for the direct electrons, i.e., the electrons that after liberation go directly to the detector. In this case, the dependence on the molecular orientation is far more pronounced for a bichromatic driving field.

Observing Axial Chirality of Chiral Single-Wall Carbon Nanotubes by Helicity-Dependent Raman Spectra.

Helicity-dependent Raman spectra of an isolated, chiral, single-wall carbon nanotube (SWNT) are reported using circularly polarized light. A polar plot of polarized Raman intensity for the radial breathing mode (RBM), which is excited by left-handed or right-handed circularly polarized light, shows asymmetric angle dependence relative to the nanotube axis direction, which reflects the axial chirality of a SWNT. The asymmetry in the polar plot of the RBM can be analyzed by a complex Raman tensor. The complex phase of each component of the Raman tensor has a maximum at chiral angle θ = 15° of a SWNT which is between two achiral SWNTs, that is, zigzag (θ = 0°) and armchair (θ = 30°) SWNTs. Considering the interaction between the chiral SWNT and the circularly polarized light, we discuss the origin of the complex phases excited by the opposite helicity of the circularly polarized light.

Elliptical high-order harmonic generation from current-carrying orbitals of prealigned molecules

The polarization of high harmonics generated from current-carrying state of nitric oxide molecules irradiated by linear laser fields is investigated by numerically solving the three-dimensional time-dependent Schrödinger equation. It is found that the ellipticity of high harmonics is obviously dependent on the polar angle between the driving laser polarization and molecular axis which is interpreted by the strong field approximation model. Moreover, our results also show that the helicity of near-threshold harmonics is opposite to that of plateau harmonics when the molecule is at any polar angle. To analyze this phenomenon, we simulate the dipole matrix element numerically. Finally, the attosecond pulses with opposite helicities can be obtained by synthesizing near-threshold and plateau harmonics. The ellipticity can be tuned by the alignment angle of molecules. Our work may provide a theoretical guiding and detection tool for the electron dynamics of molecular current-carrying states.

Self-Assembly of Cone-Shaped Subphthalocyanines: A Theoretical Insight

Compared to planar phthalocyanines, cone-shaped subphthalocyanines (SubPcs) exhibit axial dipole moments, giving rise to polarly ordered materials when piled up in columns, and become intrinsically chiral when properly substituted. Furthermore, owing to their rigid conic structure, SubPcs display a convex side (a head) and a concave side (a tail) and their intermolecular stacking interactions may lead to centrosymmetric head-to-head and tail-to-tail and to noncentrosymmetric head-to-tail aggregation geometries.In this contribution, we perform a theoretical study on the aggregation modes of the C 3-symmetric boron SubPc 1, in which the central boron atom is substituted with a small, highly electronegative fluorine atom and the SubPc core is decorated with arilamide groups giving rise to 1P and 1M enantiomers (Figure 1). Depending solely on the solvent nature (aromatic or aliphatic), π-conjugated SubPc 1 can self-assemble either in a tail-to-tail dimer (regime A) or in a head-to-tail columnar stack (regime B), formed via a nucleation-elongation polymerization mechanism.1 Furthermore, 1P and 1M enantiomers give rise to homochiral assemblies with opposite helicities.2 Calculations indicate that whereas the SubPc enantiomers socially self-sort in the polymer regime, showing an alternate columnar stacking order, they reveal narcissistic self-sorting in the dimer regime, each enantiomer disclosing a strong preference to associate with itself.

Temperature Directs the Majority-Rules Principle in Supramolecular Copolymers Driven by Triazine-Benzene Interactions.

Supramolecular copolymers have typically been studied in the extreme cases, such as self-sorting or highly mixed copolymer systems, while the intermediate systems have been less understood. We have reported the temperature-dependent microstructure in copolymers of triazine- and benzene-derivatives based on charge-transfer interactions with a highly alternating microstructure at low temperatures. Here, we investigate the temperature-dependent copolymerization further and increase the complexity by combining triazine- and benzene-derivatives with opposite preferred helicities. In this case, intercalation of the benzene-derivative into the triazine-derivative assemblies causes a helical inversion. The inversion of the net helicity was rationalized by comparing the mismatch penalties of the individual monomers, which indicated that the benzene-derivative dictates the helical screw-sense of the supramolecular copolymers. Surprisingly, this was not reflected in further investigations of slightly modified triazine- and benzene-derivatives, thus highlighting that the outcome is a subtle balance between structural features, where small differences can be amplified due to the competitive nature of the interactions. Overall, these findings suggest that the temperature-dependent microstructure of triazine- and benzene-based supramolecular copolymers determines the copolymer helicity of the presented system in a similar way as the mixed majority-rules phenomenon.

A Reversed Inverse Faraday Effect

The inverse Faraday effect is a magneto‐optical process allowing the magnetization of matter by an optical excitation carrying a non‐zero spin. In particular, a right circular polarization generates a magnetization in the direction of light propagation and a left circular polarization in the opposite direction to this propagation. Herein, it demonstrates that by manipulating the spin density of light, i.e., its polarization, in a plasmonic nanostructure, a reversed inverse Faraday effect is generated. A right circular polarization will generate a magnetization in the opposite direction of the light propagation, a left circular polarization in the direction of propagation. Also, it demonstrates that this new physical phenomenon is chiral, generating a strong magnetic field 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 processing technologies.

Stacked or Folded? Impact of Chelate Cooperativity on the Self-Assembly Pathway to Helical Nanotubes from Dinucleobase Monomers.

Self-assembled nanotubes exhibit impressive biological functions that have always inspired supramolecular scientists in their efforts to develop strategies to build such structures from small molecules through a bottom-up approach. One of these strategies employs molecules endowed with self-recognizing motifs at the edges, which can undergo either cyclization-stacking or folding-polymerization processes that lead to tubular architectures. Which of these self-assembly pathways is ultimately selected by these molecules is, however, often difficult to predict and even to evaluate experimentally. We show here a unique example of two structurally related molecules substituted with complementary nucleobases at the edges (i.e., G:C and A:U) for which the supramolecular pathway taken is determined by chelate cooperativity, that is, by their propensity to assemble in specific cyclic structures through Watson-Crick pairing. Because of chelate cooperativities that differ in several orders of magnitude, these molecules exhibit distinct supramolecular scenarios prior to their polymerization that generate self-assembled nanotubes with different internal monomer arrangements, either stacked or coiled, which lead at the same time to opposite helicities and chiroptical properties.

Static and dynamic magnetic characteristics in concentric permalloy nanorings

Magnetic nanodisks and nanorings have been focus of attention for quite some time due to their applicability in magnetic memory devices. In this paper, static and dynamic magnetic properties of Permalloy concentric thin ring nanostructures are reported as a function of the number of rings by using micromagnetic simulations. The maximum outer radius (R) and thickness (t) of the concentric rings are fixed at 100 nm and 20 nm respectively. The distance between any two neighbouring rings is always maintained equal to the width of each ring while the number of nanorings is increased starting from one to five. In-plane magnetic hysteresis loops show that in all cases, the remanence and coercivity values are found to be almost zero while vortex state is exhibited with opposite helicity in adjacent nanorings. When the number of nanorings reach five, the narrowest hysteresis loop is observed with almost no hysteresis at all. Dynamic susceptibility spectra was computed by relaxing the system from a out of plane saturated state followed by an in-plane excitation using a small field pulse. In most of the cases, the in plane magnetic field pulse excites azimuthal spin wave modes. The resonance frequency corresponding to these excitation modes depends on the remanent configuration and the number of peaks increase with increment in the number of rings. The ferromagnetic resonance mode that is common for all the samples considered, moves towards lower frequency with increase in number of concentric rings.