Degree Of Chirality Research Articles

Remote chirality transfer in low-dimensional hybrid metal halide semiconductors.

In hybrid metal halide perovskites, chiroptical properties typically arise from structural symmetry breaking by incorporating a chiral A-site organic cation within the structure, which may limit the compositional space. Here we demonstrate highly efficient remote chirality transfer where chirality is imposed on an otherwise achiral hybrid metal halide semiconductor by a proximal chiral molecule that is not interspersed as part of the structure yet leads to large circular dichroism dissymmetry factors (gCD) of up to 10-2. Density functional theory calculations reveal that the transfer of stereochemical information from the chiral proximal molecule to the inorganic framework is mediated by selective interaction with divalent metal cations. Anchoring of the chiral molecule induces a centro-asymmetric distortion, which is discernible up to four inorganic layers into the metal halide lattice. This concept is broadly applicable to low-dimensional hybrid metal halides with various dimensionalities (1D and 2D) allowing independent control of the composition and degree of chirality.

Spatiotemporal-Dependent Confinement Effect of Bubble Swarms Enables a Fractal Hierarchical Assembly with Promoted Chirality.

The submarine-confined bubble swarm is considered an important constraining environment for the early evolution of living matter due to the abundant gas/water interfaces it provides. Similarly, the spatiotemporal characteristics of the confinement effect in this particular scenario may also impact the origin, transfer, and amplification of chirality in organisms. Here, we explore the confinement effect on the chiral hierarchical assembly of the amphiphiles in the confined bubble array stabilized by the micropillar templates. Compared with the other confinement conditions, the assembly in the bubble scenario yields a fractal morphology and exhibits a unique level of the chiral degree, ordering, and orientation consistency, which can be attributed to the characteristic interfacial effects of the rapidly formed gas/water interfaces. Thus, molecules with a balanced amphiphilicity can be more favorable for the promotion. Not limited to the pure enantiomers, chiral amplification of the enantiomer-mixed assembly is observed only in the bubble scenario. Beyond the interfacial mechanism, the fast formation kinetics of the confined liquid bridges in the bubble scenario endows the assembly with the tunable hierarchical morphology when regulating the amphiphilicity, aggregates, and confined spaces. Furthermore, the chiral-induced spin selectivity (CISS) effect of the fractal hierarchical assembly was systematically investigated, and a strategy based on photoisomerization was developed to efficiently modulate the CISS effect. This work provides insights into the robustness of confined bubble swarms in promoting a chiral hierarchical assembly and the potential applications of the resulting chiral hierarchical patterns in solid-state spintronic and optical devices.

Utilizing topological invariants for encoding and manipulating chiral phonon devices

As a fundamental degree of freedom, phonon chirality is expected to promote the development of quantum information technology just like electron spin. Currently, central to this area is the realization of efficient transmission and control of chiral information. In this paper, we propose an approach by integrating topological theory, leveraging topologically invariant Chern numbers, to encode hexagonal lattice systems. Our investigation reveals the presence of topologically protected chiral interface states within the shared band gaps of both trivial and non-trivial system units. By precisely modulating the magnetic field distribution within the encoding system, we can effectively manipulate the topological pathways. Building upon this framework, we design and implement a chiral phonon three-port device. Through dynamic calculations, we demonstrate the transmission process of chiral information, showcasing the chiral phonon switching effect and logical OR operation. Our findings not only establish a fundamental mechanism for the manipulation and control of phonon chiral information but also provide a promising direction for research in harnessing chirality degrees of freedom in practical applications.

Graph‐theoretical chirality measure and chirality–property relations for chemical structures with multiscale mirror asymmetries

AbstractChirality is an essential geometric property unifying small molecules, biological macromolecules, inorganic nanomaterials, biological microparticles, and many other chemical structures. Numerous chirality measures have attempted to quantify this geometric property of mirror asymmetry and to correlate these measures with physical and chemical properties. However, their utility has been widely limited because these correlations have been largely notional. Furthermore, chirality measures also require prohibitively demanding computations, especially for chiral structures comprised of thousands of atoms. Acknowledging the fundamental problems with quantification of mirror asymmetry, including the ambiguity of sign‐variable pseudoscalar chirality measures, we revisit this subject because of the significance of quantifying chirality for quantitative biomimetics and describing the chirality of nanoscale materials that display chirality continuum and scale‐dependent mirror asymmetry. We apply the concept of torsion within the framework of differential geometry to the graph theoretical representation of chiral molecules and nanostructures to address some of the fundamental problems and practical limitations of other chirality measures. Chiral gold clusters and other chiral structures are used as models to elaborate a graph‐theoretical chirality (GTC) measure, demonstrating its applicability to chiral materials with different degrees of chirality at different scales. For specific cases, we show that GTC provides an adequate description of both the sign and magnitude of mirror asymmetry. The direct correlations with macroscopic properties, such as chiroptical spectra, are enhanced by using the hybrid chirality measures combining parameters from discrete mathematics and physics. Taking molecular helices as an example, we established a direct relation between GTC and optical activity, indicating that this chirality measure can be applied to chiral metamaterials and complex chiral constructs.

Rydberg Platform for Nonergodic Chiral Quantum Dynamics.

We propose a mechanism for engineering chiral interactions in Rydberg atoms via a directional antiblockade condition, where an atom can change its state only if an atom to its right (or left) is excited. The scalability of our scheme enables us to explore the many-body dynamics of kinetically constrained models with unidirectional character. We observe nonergodic behavior via either scars, confinement, or localization, upon simply tuning the strength of two driving fields acting on the atoms. We discuss how our mechanism persists in the presence of classical noise and how the degree of chirality in the interactions can be tuned, opening towards the frontier of directional, strongly correlated, quantum mechanics using neutral atoms arrays.

A Relationship between the Molecular Parity-Violation Energy and the Electronic Chirality Measure.

When the weak forces producing parity-violating effects are taken into account, there is a tiny energy difference between the total electronic energies of two enantiomers (ΔEPV), which might be the key to understanding the evolution of the biological homochirality. We focus on the electronic chirality measure (ECM), a powerful descriptor based on the electronic charge density, for quantifying the chirality degree of a molecule, in a representative set of chiral molecules, together with their EPV energies. Our results show a novel, strong, and positive correlation between ΔEPV and ECM, supporting a subtle interplay between the weak forces acting within the nuclei of a given molecule and its chirality. These findings suggest that experimental investigations for molecular parity violation detection should consider molecules with ECM values as large as possible and may support that a chiral signature is imprinted on life by fundamental physics via the parity-violating weak interactions.

High-pressure induced Weyl semimetal phase in 2D Tellurium

Relativistic Weyl fermion quasiparticles in Weyl semimetal bring the electron’s chirality degree of freedom into the electrical transport and give rise to exotic phenomena. A topological phase transition from a topological trivial phase to a topological non-trivial phase offers a route to control electronic devices through its topological properties. Here, we report the Weyl semimetal phase in hydrothermally grown two-dimensional Tellurium (2D Te) induced by high hydrostatic pressure (up to 2.47 GPa). The unique chiral crystal structure gives rise to chiral fermions with different topological chiral charges ({{C}}=-{{1}},+{{1}},{{and}}-{{2}}). The highly tunable chemical potential in 2D Te provides comprehensive information for understanding the pressure-dependent electron band structure. The pressure-induced insulator-to-metal transition, two-carrier transport, and the non-trivial π Berry phase shift in quantum oscillations are observed in the 2D Te Weyl semimetal phase. Our work demonstrates the pressure-induced bandgap closing in the inversion asymmetric narrow bandgap semiconductor 2D Te.

Characterization of Chiral Near Field Within Nanogaps Using Surface‐Enhanced Raman Scattering

AbstractChiral nanogap antennas, which exhibit specific chiroptical responses, hold exceptional potential in various chiral applications, including polarization converters, asymmetric catalysis, label‐free chiral recognition, and chiral sensing. However, characterizing the chiral optical fields within nanogaps presents considerable challenges owing to their complex light field responses and spatial dimensions. In this study, the strong modulation of helicity‐resolved surface‐enhanced Raman spectroscopy (SERS) signals in graphene by chiral plasmonic antennas, offering a promising approach to characterize chiral near fields within nanogaps is demonstrated. The SERS of achiral monolayer graphene is performed within plasmonic nanogap antennas, including single gold nanorods (GNRs) and GNR dimers on gold microflakes. The Raman scattering intensity of graphene within these nanogap antennas is enhanced approximately sixfold. Furthermore, the degree of cross‐circularly polarized Raman intensity reaches up to ≈45%, indicating a robust chiral optical field. Moreover, under opposite circularly polarized light excitation, the SERS of graphene reveals varying emission intensities attributed to the modulation arising from the chiral antennas in both the excitation and emission processes of Raman scattering. Furthermore, the degree of chirality depends on the antenna configuration and the excitation laser wavelength.

Chirality-dependent energy induced by spin-orbit torque-driven artificial spin texture

Recently, vast research has been under investigation on the role of chirality in magnetization dynamics, an area that currently lacks a comprehensive understanding. To gain further insight into the importance of chirality, we explore the effects of varying the degree of chirality. To investigate these effects, we have fabricated samples with perpendicular magnetic anisotropy symmetry breaking through local helium ion irradiation with various azimuthal angles and degrees of irradiation. In this system, the spin-orbit torque can induce artificial spin texture, and our azimuthal angle and degree of chirality dependent results reveal a clear cosine dependence and a nonlinear increase, respectively. It implies the system not only follows the energy contribution of interfacial Dzyaloshinskii-Moriya interaction but also has a nonlinear impact depending on anisotropy asymmetry induced chirality differences. These experimental observations are consistent with our theoretical model and micromagnetic simulations, supporting our experimental results. Overall, our findings provide further insights into the role of chirality in magnetization dynamics and may have important implications for the development of future magnetic devices.

A Method for Calculating the Sign and Degree of Chirality of Supercoiled Protein Structures

Chirality plays an important role in studies of natural protein structures. Therefore, much attention is paid to solving the problems associated with the development of criteria and methods for assessing the chirality of biomolecules. In this paper, a new method for calculating the sign and degree of chirality of superhelices is proposed. The method makes it possible to characterize the chirality sign and to quantify coiled-coils and collagen superhelices. The degree of chirality is understood as a value indicating the intensity of twisting of individual helices around the axis of the superhelix. The calculation requires information about the relative spatial arrangement of the alpha carbon of the amino acid residues of the helices that make up the superhelix. The use of a small amount of raw data makes the method easy to apply, and the validity of the results of this study is confirmed through the analysis of real protein structures.

High orbital angular momentum lasing with tunable degree of chirality in a symmetry-broken microcavity

Chiral lasers with orbital angular momenta (OAM) are building blocks in developing high-dimensional integrated photonic devices. However, it remains demanding to arbitrarily manipulate the precise degree of chirality (DOC) and quantum numbers of OAM in microscale lasers. This study reports a strategy to generate OAM microlasers with tunable DOCs and large quantum numbers through a ring-structured Fabry–Perot microcavity with nanoscale symmetry-broken geometry. By exploiting the uneven potential of photons distributed in a microcavity, the dissymmetry factor of OAM laser can be continuously tuned from −1 to +1 by manipulating optical pump positions. High-order OAM with tunable quantum numbers were also demonstrated, in which the largest quantum number reached up to 352. Finally, multivortex laser generation on-chip in spatial and temporal domains was accomplished. This study reveals the fundamental physics of symmetry-broken cavity and provides a simple yet scalable approach for manipulating the chirality of OAM microlasers, offering insights for high-dimensional information processing and optical communications.

Tunable Circular Photogalvanic and Photovoltaic Effect in 2D Tellurium with Different Chirality.

Chirality arises from the asymmetry of materials, where two counterparts are the mirror image of each other. The interaction between circular-polarized light and quantum materials is enhanced in chiral space groups due to the structural chirality. Tellurium (Te) possesses the simplest chiral crystal structure, with Te atoms covalently bonded into a spiral atomic chain (left- or right-handed) with a periodicity of 3. Here, we investigate the tunable circular photoelectric responses in 2D Te field-effect transistors with different chirality, including the longitudinal circular photogalvanic effect induced by the radial spin texture (electron-spin polarization parallel to the electron momentum direction) and the circular photovoltaic effect induced by the chiral crystal structure (helical Te atomic chains). Our work demonstrates the controllable manipulation of the chirality degree of freedom in materials.

Two Chiral YbIII Enantiomeric Pairs with Distinct Enantiomerically Pure N-Donor Ligands Presenting Significant Differences in Photoluminescence, Circularly Polarized Luminescence, and Second-Harmonic Generation.

Using enantiomerically pure bidentate and tridentate N-donor ligands (1LR/1LS and 2LR/2LS) to replace two coordinated H2O molecules of Yb(tta)3(H2O)2, respectively, two eight- and nine-coordinated YbIII enantiomeric pairs, namely, Yb(tta)31LR/Yb(tta)31LS (Yb-R-1/Yb-S-1) and [Yb(tta)32LR]·CH3CN/[Yb(tta)32LS]·CH3CN (Yb-R-2/Yb-S-2), were isolated, in which Htta = 2-thenoyltrifluoroacetone, 1LR/1LS = (-)/(+)-4,5-pinene-2,2'-bipyridine, and 2LR/2LS = (-)/(+)-2,6-bis(4',5'-pinene-2'-pyridyl)pyridine. Interestingly, they not only present distinct degrees of chirality but also show large differences in near-infrared (NIR) photoluminescence (PL), circularly polarized luminescence (CPL), and second-harmonic generation (SHG). Eight-coordinated Yb-R-1 with an asymmetric bidentate 1LR ligand has a high NIR-PL quantum yield (1.26%) and a long decay lifetime (20 μs) at room temperature, being more than two times those (0.48%, 8 μs) of nine-coordinated Yb-R-2 with a C2-symmetric tridentate 2LR ligand. In addition, Yb-R-1 displays an efficient CPL with a luminescence dissymmetry factor glum = 0.077, being 4 × Yb-R-2 (0.018). In particular, Yb-R-1 presents a strong SHG response (0.8 × KDP), which is 8 × Yb-R-2 (0.1 × KDP). More remarkably, the precursor Yb(tta)3(H2O)2 exhibits a strong third-harmonic generation (THG) response (41 × α-SiO2), while the introduction of chiral N-donors results in the switching of THG to SHG. Our interesting findings provide new insights into both the functional regulation and switching in multifunctional lanthanide molecular materials.

Chirality logic gates.

The ever-growing demand for faster and more efficient data transfer and processing has brought optical computation strategies to the forefront of research in next-generation computing. Here, we report a universal computing approach with the chirality degree of freedom. By exploiting the crystal symmetry-enabled well-known chiral selection rules, we demonstrate the viability of the concept in bulk silica crystals and atomically thin semiconductors and create ultrafast (<100-fs) all-optical chirality logic gates (XNOR, NOR, AND, XOR, OR, and NAND) and a half adder. We also validate the unique advantages of chirality gates by realizing multiple gates with simultaneous operation in a single device and electrical control. Our first demonstrations of logic gates using chiral selection rules suggest that optical chirality could provide a powerful degree of freedom for future optical computing.

Magnetoresistive Single‐Molecule Junctions: the Role of the Spinterface and the CISS Effect

AbstractThis review is an effort in putting together the latest results about room‐temperature magnetoresistive (MR) effects in nanoscale/single‐molecule electronic devices consisting of one (few) molecule(s) placed in electrical contact between two nanoscale electrodes. Molecules represent powerful building blocks for developing state‐of‐the‐art MR devices, as they bring long spin relaxation timescales, low cost and high tunability of their electrical and magnetic properties via chemical modifications. The capability to control at room temperature and under bespoke electrodes’ magnetization the MR response of a single‐molecule (SM) device has been a longstanding quest. Such SM platforms could serve as fundamental tools to understand what the main mechanistic ingredients of MR effects in a molecular device are, leading to their use as building‐blocks for miniaturization in spintronic applications. The work carried out so far in this field has identified two key components directly involved in the MR response of a single(few)‐molecule(s) device: (i) The molecule|electrode spinterface, defining the interplay between interfacial electrostatics and spin density, has been proven to play a fundamental role in the interpretation of the observed single‐molecule junction's MR effects, which is governed by the electrode material and the electrode‐molecule chemistry. (ii) Two aspects of the molecular structure have been demonstrated to be involved in the spin‐dependent conduction mechanism: (1) the presence of paramagnetic metal centres in the molecular structure and how their orbitals bearing the unpaired electrons couple with the device electrodes, and (2), the degree of chirality within the molecular wire. This contribution will focus on the above points (i‐ii) by making use of specific examples in the literature.

Spontaneous crystallization of chiral active colloidal particles

The crystallization dynamics of chiral active colloids are explored numerically. It is found that chiral colloids with large angular velocity could be localized by self-trapping, which promotes the formation of hexagonal crystal structures. The competition between chirality and coupling strength leads to the transition between liquid and solid regimes. Comparing to the achiral particles, the transition points shift towards the weak coupling region greatly with the increasing degree of chirality. The hexagonal structure seems more tenacious and more difficult to melt. Therefore, the solid–liquid coexistence region shrinks in the phase diagram. In the low rotational speed region, active particles swap neighbors rapidly, the system becomes globally ordered but undergoes a nonnegligible diffusion, leading to the structural ordering occurrence before dynamical freezing.

Activating magnetoelectric optical properties by twisting antiferromagnetic bilayers

Twisting in bilayers introduces structural chirality with two enantiomers, i.e., left- and right-hand bilayers, depending on the oriented twist angle. The interplay between this global chirality and additional degrees of freedom, such as magnetic ordering and the local octahedral chirality arising from the geometry of the bonds, can yield striking phenomena. In this work, we focus on collinear antiferromagnetic CrI$_3$ twisted homo-bilayers, which are characterized by a staggered octahedral chirality in each monolayer. Using symmetry analysis, density functional theory and tight-binding model calculations we show that layers twisting can lower the structural and magnetic point-group symmetries, thus activating pyroelectricity and the magneto-optical Kerr effect, which would otherwise be absent in untwisted antiferromagnetic homo-bilayers. Interestingly, both electric polarization and Kerr angle are controllable by the twist angle and their sign is reversed when switching from left- to right-twisted bilayers. We further unveil the occurrence of unconventional vortices with spin textures that alternate opposite chiralities in momentum space. These findings demonstrate that the interplay between twisting and octahedral chirality in magnetic bilayers and related van der Waals heterostructures represents an extraordinary resource for tailoring their physical properties for spintronic and optoelectronic applications.

Chirality-induced one-way quantum steering between two waveguide-mediated ferrimagnetic microspheres

One-way quantum steering is of importance for quantum technologies, such as secure quantum teleportation. In this paper, we study the generation of one-way quantum steering between two distant yttrium iron garnet (YIG) microspheres in chiral waveguide electromagonics. We consider that the magnon mode with the Kerr nonlinearity in each YIG sphere is chirally coupled to left- and right-propagating guided photons in the waveguide. We find that quantum steering between the magnon modes is absent with non-chirality but is present merely in the form of one way (i.e., one-way steering) when the chirality occurs. The maximal achievable steering is obviously improved as the chirality degree increases. We further find that when the waveguide's outputs are subjected to continuous homodyne detection, the steering can be considerably enhanced and asymmetric steering with strong entanglement can also be achieved by tuning the chirality. Our study shows that chirality can be explored to effectively realize one-way quantum steering. Compared to other studies on achieving asymmetric steering via controlling intrinsic dissipation, e.g. cavity loss rates, our scheme merely depends on the chirality enabled via positioning the micromagnets in the waveguide and is continuously adjustable and experimentally more feasible.

Nonreciprocal Transport in Noncoplanar Magnetic Systems without Spin–Orbit Coupling, Net Scalar Chirality, or Magnetization

We propose a new mechanism of nonlinear nonreciprocal transport in magnetic systems. By considering a noncoplanar magnetic ordering on a bilayer triangular lattice, we clarify that a local scalar chirality degree of freedom is a source of nonreciprocal transport, which does not require any relativistic spin-orbit coupling, net scalar chirality, and net magnetization. We show a close relationship between the asymmetric band modulation and the nonreciprocal transport under the noncoplanar magnetic ordering based on the model-parameter dependences in the real-space picture.

Orientation-averaged light scattering by nanoparticle clusters: Far-field and near-field benchmarks of numerical cubature methods

The optical properties of nanoparticles can be substantially affected by their assembly in compact aggregates. This is a common situation notably for nanoparticles synthesised and self-assembled into rigid clusters in colloidal form, where they may be further characterised or used in spectroscopic applications. The theoretical description of such experiments generally requires averaging the optical response over all possible cluster orientations, as they randomly orient themselves over the course of a measurement. This averaging is often done numerically by simulating the optical response for several directions of incidence, using a spherical cubature method. The simulation time increases with the number of directions and can become prohibitive, yet few studies have examined the trade-off between averaging accuracy and computational cost. We benchmark seven commonly-used spherical cubature methods for both far-field and near-field optical responses for a few paradigmatic cluster geometries: dimers of nanospheres and of nanorods, and a helix. The relative error is rigorously evaluated in comparison to analytical results obtained with the superposition T-matrix method. Accurate orientation averaging is especially important for quantities relating to optical activity, the differential response to left and right circularly polarised light, and our example calculations include in particular far-field circular dichroism and near-field local degree of optical chirality.