Chiral Coupling Research Articles

Chiral Phonon, Valley Polarization, and Inter/Intravalley Scattering in a van der Waals ReSe2 Semiconductor.

Exploring valley manipulatable layered semiconductors is highly significant for valleytronic devices. Here, we report the phonon chirality and resulting inter/intravalley scattering in valley polarized van der Waals (vdW) layered ReSe2 by linearly/circularly polarized Raman (L/CPR), transmission (L/CPT), and photoluminescence (L/CPL) spectroscopic techniques. L/CPR combined with scanning transmission electron microscopy determines the Re chains' direction and displays the existence of chiral phonons. The LPT discloses the energetic valley polarization between the Re chains and its perpendicular crystal axis directions. Intriguingly, the valley polarization strength depends on the layer thickness even in a micrometer scale and abnormaly increases with temperature increase. Further, CPT manifests the optical rotation in ReSe2 due to strong chiral phonon-photon coupling. More essentially, L/CPL unveils a strong exciton-like effect (Stokes shift) that can be interpreted from the inter/intravalley scattering related to the (chiral) phonon-carrier coupling. This investigation suggests a promising platform based on a low-symmetry vdW ReSe2 semiconductor for exploring valley physics and fabricating valley(opto)tronic nanodevices.

Topological elastic wave transport and manipulation in three-dimensional metamaterials stacked with sandwich plates

Topological metamaterials demonstrate unprecedented wave manipulation abilities with topologically protected robustness, which have been extensively investigated in one-dimensional (1D) and two-dimensional (2D) mechanical systems, but less explored in three-dimensional (3D) systems. In this study, a 3D topological mechanical metamaterial with periodically stacked sandwich metamaterial plates is proposed to achieve 2D topological surface wave transport in a relatively low-frequency range. An innovative chiral compression-torsion coupling core is employed on the sandwich metamaterial plate to lower the band frequency. Analogous to the quantum valley Hall effect, the two-fold topological nodal line is lifted by breaking the spatial inversion symmetry, opening a topological band gap. By supercell analysis, the topological interface state is demonstrated to appear at the interface of two topologically different domains, and the topological boundary state can also be excited under appropriate free or fixed boundary conditions. Taking advantage of the 3D periodicity, the wave propagation based on both topological interface states and boundary states is examined in both 2D flat plates and 3D structures, realizing 1D topological waveguide and 2D topological surface wave transport respectively. It is found that mode symmetry matching is crucial for constructing the topological wave transport with both interface and boundary states. Leveraging the dependence of boundary states on boundary conditions, this work innovatively presents route-switchable and layer-selective wave manipulation by controlling boundary conditions without complicated structure design, enriching the strategies for tunable elastic wave manipulation. Besides, the topologically protected surface wave transport is demonstrated by introducing defects and disorders. These findings provide new insights into the topological transport of elastic waves in 3D mechanical metamaterials and contribute to the development of intelligent and robust devices for various purposes, such as vibration mitigation, energy harvesting, and signal sensing.

Chiral plasmonic-dielectric coupling enables strong near-infrared chiroptical responses from helicoidal core-shell nanoparticles

Helicoid plasmonic nanoparticles with intrinsic chirality are an emerging class of artificial chiral materials with tailorable properties. The ability to extend their chiroplasmonic responses to the near-infrared (NIR) range is critically important for biomedical and nanophotonic applications, yet the rational design of such materials remains challenging. Herein, a strategy employing chiral plasmon-dielectric coupling is proposed to manipulate the chiroptical responses into the NIR region with high optical anisotropy. Through this strategy, the helicoid Au@Cu2O nanoparticles with structural chirality are designed and synthesized with tunable and enriched NIR chiroptical responses. Specially, a high optical anisotropy (g-factor) with a value of 0.35 is achieved in the NIR region, and multi-band chiroptical behaviors are observed. Spectral and electromagnetic simulations elucidate that strong coupling between chiroplasmonic core and chiral dielectric shell with high refractive index contributes to the rich and strong chiroptical responses, which are related to the interplay between various emerged and enhanced electric and magnetic multipolar resonance modes proved by multipole expansion analysis. Moreover, the helicoid Au@Cu2O nanoparticles display greater polarization rotation capability than the helicoid Au nanoparticles. This work offers mechanistic insights into chiral plasmon-dielectric coupling and suggests a general approach of creating NIR chiroplasmonic materials.

Control of spin–orbit torque-driven domain nucleation through geometry in chirally coupled magnetic tracks

The interfacial Dzyaloshinskii–Moriya interaction (DMI) can be exploited in magnetic thin films to realize lateral chirally coupled systems, providing a way to couple different sections of a magnetic racetrack and realize interconnected networks of magnetic logic gates. Here, we systematically investigate the interplay between spin–orbit torques, chiral coupling, and the device design in domain wall racetracks. We show that the current-induced domain nucleation process can be tuned between single-domain nucleation and repeated nucleation of alternate domains by changing the orientation of an in-plane patterned magnetic region within an out-of-plane magnetic racetrack. Furthermore, by combining experiments and micromagnetic simulations, we show that the combination of damping-like and field-like spin–orbit torques with DMI results in selective domain wall injection in one of two arms of a Y-shaped device depending on the current density. Such an element constitutes the basis of domain wall based demultiplexer, which is essential for distributing a single input to any one of the multiple outputs in logic circuits. Our results provide input for the design of reliable and multifunctional domain wall circuits based on chirally coupled interfaces.

Entanglement enhancement of two giant atoms with multiple connection points in bidirectional-chiral quantum waveguide-QED system

We study the entanglement generation of two giant atoms within a one-dimensional bidirectional-chiral waveguide quantum electrodynamics (QED) system, where the initial state of the two giant atoms are ∣e a , g b 〉. Here, each giant atom is coupled to the waveguide through three connection points, with the configurations divided into five types based on the arrangement of coupling points between the giant atoms and the waveguide: separate, fully braided, partially braided, fully nested, and partially nested. We explore the entanglement generation process within each configuration in both nonchiral and chiral coupling cases. It is demonstrated that entanglement can be controlled as needed by either adjusting the phase shift or selecting different configurations. For nonchiral coupling, the entanglement of each configuration exhibits steady state properties attributable to the presence of dark state. In addition, we find that steady-state entanglement can be obtained at more phase shifts in certain configurations by increasing the number of coupling points between the giant atoms and the bidirectional waveguide. In the case of chiral coupling, the entanglement is maximally enhanced compared to the one of nonchiral case. Especially in fully braided configuration, the concurrence reaches its peak value 1, which is robust to chirality. We further show the influence of atomic initial states on the evolution of interatomic entanglement. Our scheme can be used for entanglement generation in chiral quantum networks of giant-atom waveguide-QED systems, with potential applications in quantum networks and quantum communications.

Torsional vibration suppression of a gear-rotor system using an inerter magnet nonlinear energy sink

The novel inerter magnet nonlinear energy sink (IMNES) utilizes chiral compression-torsion coupling effects to achieve mass augmentation, effectively mitigating torsional vibrations in a gear-rotor system with gear meshing clearance. The positive stiffness generated by the piecewise linear beam combines with the negative stiffness produced by the permanent magnet pair, resulting in the establishment of the IMNES’s nonlinear stiffness. Subsequently, a dynamic model of the IMNES-gear-rotor system is developed. Optimal parameters for the IMNES are determined through analysis of vibrational response surfaces under both transient and steady-state conditions. The numerical calculation of torsional vibration in the IMNES-gear rotor system is conducted across various gear meshing clearances. The results demonstrate that across different gear mesh clearances, the IMNES effectively attenuates torsional vibrations in the gear-rotor system. Under transient excitation, implementation of the IMNES leads to an 87% reduction rate in displacement within the gear-rotor system. In terms of steady-state excitation, simulations show a significant enhancement with a 65% increase in vibration suppression percentage.

BCFT One-point Functions of Coulomb Branch Operators

We show that supersymmetry can be used to compute the BCFT one-point function coefficients for chiral primary operators, in 4d N\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{N} $$\\end{document} = 2 SCFTs with 12\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\frac{1}{2} $$\\end{document}-BPS boundary conditions. The main ingredient is the hemisphere partition function, with the boundary condition on the equatorial S3. A supersymmetric Ward identity relates derivatives with respect to the chiral coupling constants to the insertion of the primaries at the pole of the hemisphere. Exact results for the one-point functions can be then obtained in terms of the localization matrix model. We discuss in detail the example of the super Maxwell theory in the bulk, interacting with 3d N\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{N} $$\\end{document} = 2 SCFTs on the boundary. In particular we derive the action of the SL(2,ℤ) duality on the one-point functions.

Strong coupling between excitons and chiral quasibound states in the continuum of the bulk WS2 metasurface.

In the fields of optics and photonics, the topic of light-matter interactions, particularly strong coupling effects, is a developing area of research. Exciton polariton, a hybridized state brought about by strong coupling, is a hot topic, especially from the standpoint of chiral optics. Under the incidence of right circularly polarized light and left circularly polarized (RCP and LCP) light, we investigate the strong coupling between excitons and quasibound states in the continuum (Q-BICs) resonance in a bulk WS2 metasurface. It is discovered that the Q-BICs are affected obviously on center frequencies and linewidth by structure parameters; while the exciton peaks are impacted insignificantly. Furtherly Q-BIC shows chiral enhancing features. When we take into account both Q-BIC and excitons of the metasurface simultaneously, there is a strong coupling as evidenced by the Rabi splitting up to 182 meV and the clear anti-crossing behavior in the transmittance and reflectance spectra of left and right circularly polarized light, respectively. Notably, a quasi-induced transparency window forms in the circular dichroism (CD) spectrum around the exciton band due to the non-chirality of exciton peaks. This enables the removal of excitons that are not involved in the strong coupling. The bulk WS2 chiral metasurface as a strong coupling system not only provides a way to understand the strong Light-matter interaction, but also generate a potential possibility for realizing the application of chiral optics. Additionally, it can realize the strong chiral coupling with a single self-hybridized element in the structure. Our results have potential implications in the chiral optical field and provide a chiral perspective on the study of strong photon-exciton coupling.

Introducing a π‐Skeleton Perpendicular to the Central Methylene Carbon in Alkanediamides: Design of Supramolecular Polymers with an Offset π‐Stacking Arrangement

AbstractThe self‐assembly behavior of a heptanediamide derivative that contains a four‐ring fused π‐skeleton on its central methylene carbon atom has been examined. This molecule, which also contains two octyl chains, gelated the nonpolar solvent methylcyclohexane through the formation of fibrous nanostructures with hydrogen‐bonding networks through a cooperative nucleation–elongation process. The supramolecular polymerization is accompanied by bathochromic shifts of both the absorption and fluorescence bands while maintaining a fluorescence quantum yield comparable to that of the monomeric state. Theoretical calculations provided an energetically stable structure, in which the π‐skeletons are stacked with an offset of more than 8.0 Å, replicating the experimentally observed absorption change due to exciton coupling. Moreover, a slow transition with an inversion of the chiral arrangement of the π‐conjugated moieties was induced by replacing the octyl chains with chiral alkyl chains. Our molecular‐design strategy was further applied to a five‐ring fused π‐skeleton, which also forms an offset π‐stacking arrangement and exhibits more effective chiral exciton coupling in the aggregated state.

Introducing a π-Skeleton Perpendicular to the Central Methylene Carbon in Alkanediamides: Design of Supramolecular Polymers with an Offset π-Stacking Arrangement.

The self-assembly behavior of a heptanediamide derivative that contains a four-ring fused π-skeleton on its central methylene carbon atom has been examined. This molecule, which also contains two octyl chains, gelated the nonpolar solvent methylcyclohexane through the formation of fibrous nanostructures with hydrogen-bonding networks through a cooperative nucleation-elongation process. The supramolecular polymerization is accompanied by bathochromic shifts of both the absorption and fluorescence bands while maintaining a fluorescence quantum yield comparable to that of the monomeric state. Theoretical calculations provided an energetically stable structure, in which the π-skeletons are stacked with an offset of more than 8.0 Å, replicating the experimentally observed absorption change due to exciton coupling. Moreover, a slow transition with an inversion of the chiral arrangement of the π-conjugated moieties was induced by replacing the octyl chains with chiral alkyl chains. Our molecular-design strategy was further applied to a five-ring fused π-skeleton, which also forms an offset π-stacking arrangement and exhibits more effective chiral exciton coupling in the aggregated state.

Giant chiral magnetoelectric oscillations in a van der Waals multiferroic

Helical spin structures are expressions of magnetically induced chirality, entangling the dipolar and magnetic orders in materials1–4. The recent discovery of helical van der Waals multiferroics down to the ultrathin limit raises prospects of large chiral magnetoelectric correlations in two dimensions5,6. However, the exact nature and magnitude of these couplings have remained unknown so far. Here we perform a precision measurement of the dynamical magnetoelectric coupling for an enantiopure domain in an exfoliated van der Waals multiferroic. We evaluate this interaction in resonance with a collective electromagnon mode, capturing the impact of its oscillations on the dipolar and magnetic orders of the material with a suite of ultrafast optical probes. Our data show a giant natural optical activity at terahertz frequencies, characterized by quadrature modulations between the electric polarization and magnetization components. First-principles calculations further show that these chiral couplings originate from the synergy between the non-collinear spin texture and relativistic spin–orbit interactions, resulting in substantial enhancements over lattice-mediated effects. Our findings highlight the potential for intertwined orders to enable unique functionalities in the two-dimensional limit and pave the way for the development of van der Waals magnetoelectric devices operating at terahertz speeds.

Switching of Circularly Polarized Luminescence via Dynamic Axial Chirality Control of Chiral Bis(Boron Difluoride) Complexes with Salen Ligands

AbstractThe intensity and handedness of circularly polarized luminescence (CPL) were successfully controlled by dynamic molecular motion in solutions. Bis(boron difluoride) complexes with chiral salen ligands were synthesized and their photophysical properties were investigated. Although these complexes showed rapid molecular rotation about the C−N bond axis in solution at room temperature, two conformers assigned as atropisomers were observed in the NMR spectra at low temperature. Furthermore, the equilibrium of these atropisomers was found to change depending on the external environment, such as the solvent and temperature, allowing precise control of the intensity and handedness of CPL without luminescence color shifts. Theoretical calculations based on density functional theory (DFT) revealed that intramolecular chiral exciton coupling is the key to changes in CPL properties.

Nonreciprocal routing of microwave photons with broad bandwidth via magnon-cavity chiral coupling.

We propose a scheme for realizing nonreciprocal microwave photon routing with two cascaded magnon-cavity coupled systems, which work around the exceptional points of a parity-time (PT)-symmetric Hamiltonian. An almost perfect nonreciprocal transmission can be achieved with a broad bandwidth, where the transmission for a forward-propagating photon can be flexibly controlled with the backpropagating photon being isolated. The transmission or isolated direction can be reversed via simply controlling the magnetic field direction applied to the magnons. The isolation bandwidth is improved by almost three times in comparison with the device based on a single PT-symmetric system. Moreover, the effect of intrinsic cavity loss and added thermal noises is considered, confirming the experimental feasibility of the nonreciprocal device and potential applications in quantum information processing.

Single-photon scattering in giant-atom waveguide systems with chiral coupling

Single-photon scattering in giant-atom waveguide systems with chiral coupling

Tunable targeted single-photon routing in a waveguide-QED structure containing a time-modulated two-level atom

Single-photon routing between two one-dimensional waveguides mediated by a single-mode cavity embedded with a time-modulated two-level atom is investigated. Two configurations, where the single photon is incident from an infinite or semi-infinite waveguide, are considered. Using the analytical expressions of the single-photon scattering amplitudes, the transmission behaviors in the two waveguides are discussed. The results show that the time modulation of the atomic frequency enables a dynamically tunable quantum router. A single photon with different frequencies can be routed dynamically from the incident waveguide to the other by properly manipulating the amplitude-to-frequency ratio of the atom. The routing efficiency can be improved to approach 100% by terminating the incident waveguide. In the semi-waveguide configuration, the routing behaviors controlled by the quantum coherent feedback are also investigated. The influence of the phase shifts introduced by the terminated waveguide on the routing capability and the conditions for perfect single-photon routing are discussed in detail. A frequency tunable targeted single-photon router can even be realized with the help of chiral coupling. These results may be beneficial to the photon control in a quantum network based on time-modulated quantum nodes.

Chiral dual-core emitters based-on through-space coupling for high-performance OLEDs with little efficiency roll-off

Through-space coupling (TSC) is the essential component of π-stacked systems and has promise in charge transport and electronic communication, which is of great significance for the construction of efficient and stable photoelectric devices. In this work, we demonstrate a chiral dual-core strategy for the design of high-performance organic circularly polarized emitters, which features of connecting two thermally activated delayed fluorescence (TADF) luminophores with chiral linkage that allows efficient TSC to occur. Using this strategy, a pair of dual-core enantiomers, R/S-DNKP, were designed and synthesized by linking two benzophenone derivatives with a 1,1′-bi-2-naphthol unit. Compared to the mono-core counterpart NKP, the dual-core emitters exhibited the photoluminescence quantum yields up to 94 %. Moreover, benefiting from their chiral helical folding configurations, the R/S-DNKP enantiomers exhibited the luminescence dissymmetry factor (|glum|) value of +2.7 × 10−3 and −2.6 × 10−3 in doped films. Notably, the electroluminescence devices based on the R/S-DNKP enantiomers achieved external quantum efficiency values of 21.5 % and 19.7 % with little roll-off. It is believed that this molecular design strategy will pave new routes for the development of high-performance chiral emitters for future organic photonic devices.

Terahertz Magnetic Moiré Grating for Enhanced Chirality Manipulation and Nonreciprocal Spin Isolation

AbstractMagneto‐optical activity is a significant way to achieve asymmetric transmission for spin photons. However, it is severely limited by the weak light‐matter interaction in the terahertz (THz) region. In this work, a magnetic Moiré grating (MMG) is constructed by sandwiching an Yttrium iron garnet (YIG) single crystal in a pair of twisted 2D subwavelength gratings. The twisted angle between two gratings introduces a strong geometric Moiré chirality related to the Moiré pattern. When an external magnetic field is applied to the YIG layer, three different symmetries of spacial mirror image, time reversal, and spin conjugation are broken simultaneously under the chiral coupling between magneto‐optical activity and Moiré chirality, leading to both the enhanced magneto‐optical chiral transmission and the nonreciprocal spin isolation. Under the magnetic field varying from −0.26 to +0.26 T in the experiment, the MMG achieves an active modulation of circular dichroism from 39 to −37.5 dB and optical activity from −35° to 30°. Moreover, the maximum spin isolation over 32.6 dB is also obtained near 0.5 THz. This mechanism provide a new way to realize independent manipulation and active modulation of THz spin photons more flexibly.

Asymmetric magnetization switching and programmable complete Boolean logic enabled by long-range intralayer Dzyaloshinskii-Moriya interaction

After decades of efforts, some fundamental physics for electrical switching of magnetization is still missing. Here, we report the discovery of the long-range intralayer Dzyaloshinskii-Moriya interaction (DMI) effect, which is the chiral coupling of orthogonal magnetic domains within the same magnetic layer via the mediation of an adjacent heavy metal layer. The effective magnetic field of the long-range intralayer DMI on the perpendicular magnetization is out-of-plane and varies with the interfacial DMI constant, the applied in-plane magnetic fields, and the magnetic anisotropy distribution. Striking consequences of the effect include asymmetric current/field switching of perpendicular magnetization, hysteresis loop shift of perpendicular magnetization in the absence of in-plane direct current, and sharp in-plane magnetic field switching of perpendicular magnetization. Utilizing the intralayer DMI, we demonstrate programable, complete Boolean logic operations within a single spin-orbit torque device. These results will stimulate investigation of the long-range intralayer DMI effect in a variety of spintronic devices.

Excitation of exchange spin waves in a magnetic insulator thin film at cryogenic temperatures

Spin waves and their quanta, magnons, are promising candidates for next-generation electronic devices, due to their low-power consumption and compatibility with radio-frequency-based electronic devices. For achieving magnon-based hybrid quantum systems for quantum memory and computation, the investigation of spin-wave propagation at cryogenic temperatures is highly required. In this article, we report the excitation and detection of exchange spin waves with wavelengths of tens of nanometers in an yttrium iron garnet (YIG) thin film at cryogenic temperatures. We find that the exchange spin waves are unidirectional in all temperature ranges, owing to the chiral dynamical dipolar coupling between the spin-wave mode in the YIG and the ferromagnetic resonance mode in the cobalt nanowire. Notably, a high exchange spin-wave group velocity of 2 km s−1 at 10 K is observed. Our results are promising for the development of high-speed and energy-efficient quantum magnonic devices operating at cryogenic temperatures.

Controllable nonreciprocal single-photon frequency converter via a four-level system

We propose an efficient, nonreciprocal single-photon device that achieves single-photon routing and frequency conversion through chiral coupling of two one-dimensional waveguides with a four-level atom. Photons incoming from one port can be definitely directed to another port. However, the photon frequency conversion has been achieved only when the single photons are transferred from one waveguide to the other, and its probability can reach unity. Applied the on-demand classical field to drive an atom, the transmission quantum tunneling path can be turned off and on by exploiting the Autler–Townes splitting mechanism. Our results illustrate the potential of our device for applications in a quantum network.