Polar Order Research Articles

Effects of self-avoidance on the packing of stiff rods on ellipsoids.

Using a statistical-mechanics approach, we study the effects of geometry and self-avoidance on the ordering of slender filaments inside nonisotropic containers, considering cortical microtubules in plant cells, and packing of genetic material inside viral capsids as concrete examples. Within a mean-field approximation, we show analytically how the shape of the container, together with self-avoidance, affects the ordering of the stiff rods. We find that the strength of the self-avoiding interaction plays a significant role in the preferred packing orientation, leading to a first-order transition for oblate cells, where the preferred orientation changes from azimuthal, along the equator, to a polar one, when self-avoidance is strong enough. While for prolate spheroids the ground state is always a polar-like order, strong self-avoidance results with a deep metastable state along the equator. We compute the critical surface describing the transition between azimuthal and polar ordering in the three-dimensional parameter space (persistence length, eccentricity, and self-avoidance) and show that the critical behavior of this system is in fact related to the butterfly catastrophe model. We calculate the pressure and shear stress applied by the filament on the surface, and the injection force needed to be applied on the filament in order to insert it into the volume. We compare these results to the pure mechanical study where self-avoidance is ignored, and discuss similarities and differences.

Revealing the three-dimensional arrangement of polar topology in nanoparticles

In the early 2000s, low dimensional ferroelectric systems were predicted to have topologically nontrivial polar structures, such as vortices or skyrmions, depending on mechanical or electrical boundary conditions. A few variants of these structures have been experimentally observed in thin film model systems, where they are engineered by balancing electrostatic charge and elastic distortion energies. However, the measurement and classification of topological textures for general ferroelectric nanostructures have remained elusive, as it requires mapping the local polarization at the atomic scale in three dimensions. Here we unveil topological polar structures in ferroelectric BaTiO3 nanoparticles via atomic electron tomography, which enables us to reconstruct the full three-dimensional arrangement of cation atoms at an individual atom level. Our three-dimensional polarization maps reveal clear topological orderings, along with evidence of size-dependent topological transitions from a single vortex structure to multiple vortices, consistent with theoretical predictions. The discovery of the predicted topological polar ordering in nanoscale ferroelectrics, independent of epitaxial strain, widens the research perspective and offers potential for practical applications utilizing contact-free switchable toroidal moments.

Concerning for the solvent-polarity-dependent conformational equilibrium and ESIPT mechanism in Pz3HC system: A novel insight

In this report, we propose a new insight into the interaction between the solvent-polarity-dependent conformational equilibrium and excited state intramolecular proton transfer (ESIPT) behavior of Pz3HC system in four different polar solvents (polarity order: ACN > THF > TOL > CYC). Using quantum chemistry method, we first announce a coexistence mechanism between Pz3HC-1 and Pz3HC-3 in the ground state in four solvents based on the Boltzmann distribution. In particular, Pz3HC-1 is the principal configuration in non-polar solvent, but Pz3HC-3 is the principal configuration in polar solvent. In addition, the simulated fluorescence spectra interprets the negative solvatochromism effect of Pz3HC-1 and Pz3HC-3 in four solvents. The evidence from intramolecular hydrogen bonding (IHB) parameters and electronic perspective collectively confirms the light-induced IHB enhancement and intramolecular charge transfer (ICT) properties in Pz3HC-1 and Pz3HC-3, which raises the likelihood of the ESIPT process. Combining the calculation of potential energy curve (PEC) and intrinsic reaction coordinate (IRC), we demonstrate that the ESIPT ease of Pz3HC-1 in different polar solvents obeys the order of CYC > TOL > THF > ACN, while the order of ESIPT ease in Pz3HC-3 is opposite. Notably, the ESIPT process of Pz3HC-3 in CYC solvent is accompanied by the twisted intramolecular charge transfer (TICT) process. In addition, we also reveal that the enol* and keto* fluorescence peaks of Pz3HC-3 in CYC solvent are quenched by ISC and TICT process, respectively. Our work not only provides a satisfactory explanation of the novel dynamics mechanism for Pz3HC system, but also brings light to the design and application of new sensing molecules in the future.

Confinement and magnetic-field effect on chiral ferroelectric nematic liquid crystals in Grandjean-Cano wedge cells.

We explore the structure and magnetic-field response of edge dislocations in Grandjean-Cano wedge cells filled with chiral mixtures of the ferroelectric nematic mesogen DIO. Upon cooling, the ordering changes from paraelectric in the cholesteric phase N^{*} to antiferroelectric in the smectic SmZ_{A}^{*} and to ferroelectric in the cholesteric N_{F}^{*}. Dislocations of the Burgers vector b equal to the helicoidal pitch P are stable in all three phases, while dislocations with b=P/2 exist only in the N^{*} and SmZ_{A}^{*}. The b=P/2 dislocations split into pairs of τ^{-1/2}λ^{+1/2} disclinations, while the thick dislocations b=P are pairs of nonsingular λ^{-1/2}λ^{+1/2} disclinations. The polar order makes the τ^{-1/2} disclinations unstable in the N_{F}^{*} phase, as they should be connected to singular walls in the polarization field. We propose a model of transformation of the composite τ^{-1/2} line-wall defect into a nonsingular λ^{-1/2} disclination, which is paired up with a λ^{+1/2} line to form a b=P dislocation. The SmZ_{A}^{*} behavior in the in-plane magnetic field is different from that of the N_{F}^{*} and N^{*}: the dislocations show no zigzag instability, and the pitch remains unchanged in the magnetic fields up to 1 T. The behavior is associated with the finite compressibility of smectic layers.

Disruption of polar order in lead zirconate titanate by composition-modulated artificial superlattice

Lead zirconate titanate (Pb (Zrx, Ti1−x)O3: PZT) is a well-known ferroelectric compound, in which long-range polar order is usually developed. In the present study, it was clarified by distortion-corrected atomic-scale scanning transmission electron microscopy imaging that long-range polar order is disrupted in PZT by utilizing composition-modulated superlattice. Shape of unit cell was unusual both in the Pb(Zr0.65Ti0.35)O3 (PZT65) and Pb(Zr0.30Ti0.70)O3 (PZT30) layers, which was due to mutual in-plane lattice constraint. By taking account of this, first-principles calculations clarified that multiple directions can be energetically favorable for lead-ion displacement, which explains a reason why long-range polar order was disrupted.

Novel NaNbO3-based relaxors featuring ultrahigh energy storage performance

Ferroelectric ceramics with ultrahigh power density and fast charging/discharging are attracting increasing attention. The practical application of most antiferroelectric ceramics in current electronics is significantly limited by their poor recoverable energy storage density. Here, a novel system ceramic of (1-x) Na0.84Ca0.16Nb0.84Ti0.16O3-xBiZn2/3Nb1/3O3 (NCNT-xBZN) solid solutions, possessing a giant Wrec∼7.05 J cm−3 and excellent conversion efficiency (η)∼83.7% under 53 kV mm−1, was synthesized to exhibit superior stability with changing temperature, frequency and fatigue behavior, together with the large current density (CD=571.8 A cm−2), ultrahigh power density (PD=85.7 MW cm−3) and ultrafast discharge rate (∼200 ns). These outstanding properties are attributed to the phase transformation from the AFE R to the FE Q phase, accompanied by the smashing of sub-microdomains into polar nanoregions, as the BZN content raises. The experimental results disclose that the synergistic effect of the highly dynamic response of polar nanoregions and the local lattice distortion arising from the disruption of long-range polar ordering by heterovalent ion filling generates a delayed saturation polarization with a strong relaxor behavior, thereby optimizing the energy storage density. The unique combination, together with a simple synthesis strategy, offers a refreshing strategy for the development of dielectric materials.

Topology-guided polar ordering of collective cell migration.

The ability of epithelial monolayers to self-organize into a dynamic polarized state, where cells migrate in a uniform direction, is essential for tissue regeneration, development, and tumor progression. However, the mechanisms governing long-range polar ordering of motility direction in biological tissues remain unclear. Here, we investigate the self-organizing behavior of quiescent epithelial monolayers that transit to a dynamic state with long-range polar order upon growth factor exposure. We demonstrate that the heightened self-propelled activity of monolayer cells leads to formation of vortex-antivortex pairs that undergo sequential annihilation, ultimately driving the spread of long-range polar order throughout the system. A computational model, which treats the monolayer as an active elastic solid, accurately replicates this behavior, and weakening of cell-to-cell interactions impedes vortex-antivortex annihilation and polar ordering. Our findings uncover a mechanism in epithelia, where elastic solid material characteristics, activated self-propulsion, and topology-mediated guidance converge to fuel a highly efficient polar self-ordering activity.

Optical Force Effects of Rayleigh Particles by Cylindrical Vector Beams.

High-order cylindrical vector beams possess flexible spatial polarization and exhibit new effects and phenomena that can expand the functionality and enhance the capability of optical systems. However, building a general analytical model for highly focused beams with different polarization orders remains a challenge. Here, we elaborately develop the vector theory of high-order cylindrical vector beams in a high numerical aperture focusing system and achieve the vectorial diffraction integrals for describing the tight focusing field with the space-variant distribution of polarization orders within the framework of Richards-Wolf diffraction theory. The analytical formulae include the exact three Cartesian components of electric and magnetic distributions in the tightly focused region. Additionally, utilizing the analytical formulae, we can achieve the gradient force, scattering force, and curl-spin force exerted on Rayleigh particles trapped by high-order cylindrical vector beams. These results are crucial for improving the design and engineering of the tightly focused field by modulating the polarization orders of high-order cylindrical vector beams, particularly for applications such as optical tweezers and optical manipulation. This theoretical analysis also extends to the calculation of complicated optical vortex vector fields and the design of diffractive optical elements with high diffraction efficiency and resolution.

Ferroelectric Smectic Liquid Crystals

Since the discovery of the first ferroelectric liquid crystal (FLC) in the chiral smectic C (SmC*) phase, ferroelectricity in liquid crystals has attracted much attention due to not only the fundamental interest but also the applications. This review focuses on the evolution of the design concept for ferroelectric smectic liquid crystals. It progresses from considering macroscopic phase symmetry to designing intermolecular interactions. For the purpose of understanding the molecular organization in smectic phases, we propose a dynamic model of constituent molecules in the smectic A (SmA) and SmC* phases based on 13C NMR studies. Then, we follow the structure–property relationship in ferroelectric SmC* liquid crystals for FLC displays. We reconsider de Vries-like materials that can provide defect-free alignment. We pay attention to the electro-optical switching in the chiral de Vries smectic A phase. Finally, we show several liquid crystals exhibiting polar smectic A phases and discuss how the polar order occurs in the highest symmetric smectic A phase.

Preliminary Phytochemical Analysis, <i>In-vitro</i> Evaluation of Antibacterial and Anticancer Activity of <i>Cleome aspera</i> Aerial Part Extracts

Various species of the Cleome genus belong to the circle of relatives Cleomaceae family, and order Brassicales, constitute flowering flora with a long record of use in conventional remedies, and have been related to the prevention of many illnesses. Cleome aspera has not been thoroughly investigated in the medicinal area; however, it may offer a therapeutic choice in favour of the management of various disorders. In this recent study, the aerial parts of C. aspera were extracted with petroleum ether, ethyl acetate, and ethanol sequentially in ascending polarity order. Ethanol extract exhibited a rich phytochemical profile and antibacterial and anti-cancer action among the solvent extracts. The phytochemical analysis of three extracts exhibited the existence of many secondary metabolites like flavonoids, alkaloids tannins, polyphenols, steroids, glycosides, and terpenoids. The antibacterial activity against two Gram (+) bacteria, Staphylococcus aureus (ATCC 6538), and Bacillus subtilis (ATCC 6633), as well as two Gram (-) bacteria, Pseudomonas aeruginosa (ATCC 9027) and Escherichia coli (ATCC 8739) was assessed at three concentrations (50, 100, 200 μg/ml) of each extract. The broth dilution method tested the extract’s minimum inhibitory concentration against four bacterial strains. Using the MTT (3-(4,5-Dimethylthiazol-2-Yl)-2,5-Diphenyltetrazolium Bromide) assay, the three extracts (petroleum ether, ethyl acetate, and ethanol) of C. aspera were evaluated for in-vitro cytotoxic activity. The extracts were detected to have substantial antibacterial activity against Gram-positive as well as Gram-negative bacteria in a dose-dependent manner. The ethanol extract of C. aspera showed notable anticancer efficacy after comparing it with petroleum ether, and ethyl acetate extracts. This study proved that the plant C. aspera has potential as a source of plant-based drugs and has therapeutic qualities like antibacterial and anticancer activities. It may provide a healing choice for the control of several diseases. A further extensive study on the isolation of active ingredients, purification, characterization, and elucidation of viable mechanisms can be executed.

Realization of sextuple polarization states and interstate switching in antiferroelectric CuInP2S6

Realization of higher-order multistates with mutual interstate switching in ferroelectric materials is a perpetual drive for high-density storage devices and beyond-Moore technologies. Here we demonstrate experimentally that antiferroelectric van der Waals CuInP2S6 films can be controllably stabilized into double, quadruple, and sextuple polarization states, and a system harboring polarization order of six is also reversibly tunable into order of four or two. Furthermore, for a given polarization order, mutual interstate switching can be achieved via moderate electric field modulation. First-principles studies of CuInP2S6 multilayers help to reveal that the double, quadruple, and sextuple states are attributable to the existence of respective single, double, and triple ferroelectric domains with antiferroelectric interdomain coupling and Cu ion migration. These findings offer appealing platforms for developing multistate ferroelectric devices, while the underlining mechanism is transformative to other non-volatile material systems.

Chiral ground states of ferroelectric liquid crystals.

Ferroelectric nematic liquid crystals are formed by achiral molecules with large dipole moments. Their three-dimensional orientational order is described as unidirectionally polar. We demonstrate that the ground state of a flat slab of a ferroelectric nematic unconstrained by externally imposed alignment directions is chiral, with left- and right-handed twists of polarization. Although the helicoidal deformations and defect walls that separate domains of opposite handedness increase the elastic energy, the twists reduce the electrostatic energy and become weaker when the material is doped with ions. This work shows that the polar orientational order of molecules could trigger chirality in soft matter with no chemically induced chiral centers.

Engineering interfacial polarization switching in van der Waals multilayers.

In conventional ferroelectric materials, polarization is an intrinsic property limited by bulk crystallographic structure and symmetry. Recently, it has been demonstrated that polar order can also be accessed using inherently non-polar van der Waals materials through layer-by-layer assembly into heterostructures, wherein interfacial interactions can generate spontaneous, switchable polarization. Here we show that deliberate interlayer rotations in multilayer van der Waals heterostructures modulate both the spatial ordering and switching dynamics of polar domains. The engendered tunability is unparalleled in conventional bulk ferroelectrics or polar bilayers. By means of operando transmission electron microscopy we show how alterations of the relative rotations of three WSe2 layers produce structural polytypes with distinct arrangements of polar domains with either a global or localized switching response. Furthermore, the presence of uniaxial strain generates structural anisotropy that yields a range of switching behaviours, coercivities and even tunable biased responses. We also provide evidence of mechanical coupling between the two interfaces of the trilayer, a key consideration for the control of switching dynamics in polar multilayer structures more broadly.

A novel accelerated trip scheme for AC grids based on open-switching traveling waves

The delayed operation of a zone-2 impedance relay for handling faults on the end-section of a protected line can exacerbate power system instability. To accelerate the trip of a zone-2 circuit breaker (CB), many accelerated trip (AT) schemes have been proposed for AC power grids. However, these schemes remain by their pre-fault operating conditions, tripping modes, fault resistance, and fault types. Considering these limitations, this paper presents a novel AT scheme based on open-switching traveling waves (TWs) generated by CB operation. First, characteristic differences in the oscillation period and wavefront polarity of the open-switching TWs generated by remote CB operation under internal, remote busbar, and external faults are analyzed. Then, an identification criterion for open-switching TWs utilizing the order and number of wavefront polarities is proposed, thereby forming a new AT scheme. Finally, based on the PSCAD/EMTDC software, the effectiveness, sensitivity, and reliability of the proposed AT scheme are verified. The proposed AT scheme can operate at high speed without being affected by pre-fault operating conditions, tripping modes, or fault types, and its ability to endure fault resistance reaches 300 Ω.

Inhibition of proliferation of human osteosarcoma cell line (MG63) by ajwain (Trachyspermum ammi L.) plant extract

Trachyspermum ammi L. (TA), popularly called ajwain, is a well-known spice plant, with fruit pods that are used in Indian traditional medicine. Fruits of this plant were scientifically investigated for medicinal properties, but no studies are reported on the vegetative parts of the plant. Hence, the present investigation is aimed to evaluate the aerial parts of the plant for anti-proliferative and antioxidant effects. Methanolic extract (Me) of TA was subjected to sequential fractionation using the solvents in the increasing order of polarity viz. hexane (He), dichloromethane (Dcm), ethyl acetate (Ea), n-butanol (n-Bu), and water (Aq). Phytochemical analyses, DPPH radical scavenging assay, and in vitro antiproliferative activity on the MG63 osteosarcoma cell line (MTT assay) were performed. Preliminary phytochemical analyses revealed the presence of reducing and non-reducing sugars, amino acids, tannins, phenols, terpenoids, and saponins. Ethyl acetate fraction showed the highest amount of total phenolics (367.90±0.02), followed by n-Bu (287.50±0.04), Dcm (193.56±0.07), Me extract (190.14±0.07), Aq (142.20±0.02) and He (80.74±0.01) fractions. Ethyl acetate fraction exhibited higher DPPH radical scavenging activity (IC50 =116.74 μg/mL) followed by n-Bu (IC50=133.81 μg/mL) fraction with a correlation to the higher amount of phenolics and flavonoids. However, maximum antiproliferative activity was exhibited by hexane fraction on MG 63 human osteosarcoma cell line which can be attributed to the presence of thymol, a monoterpenoid phenol present in ajwain. The current study indicates that the aerial parts of T. ammi Linn. can be considered as potential antioxidants and therapeutic against osteosarcoma.

A cosmological bootstrap for resonant non-Gaussianity

Recent progress has revealed a number of constraints that cosmological correlators and the closely related field-theoretic wavefunction must obey as a consequence of unitarity, locality, causality and the choice of initial state. When combined with symmetries, namely homogeneity, isotropy and scale invariance, these constraints enable one to compute large classes of simple observables, an approach known as (boostless) cosmological bootstrap. Here we show that it is possible to relax the restriction of scale invariance, if one retains a discrete scaling subgroup. We find an infinite class of solutions to the weaker bootstrap constraints and show that they reproduce and extend resonant non-Gaussianity, which arises in well-motivated models such as axion monodromy inflation. We find no evidence of the new non-Gaussian shapes in the Planck data. Intriguingly, our results can be re-interpreted as a deformation of the scale-invariant case to include a complex order of the total energy pole, or more evocatively interactions with a complex number of derivatives. We also discuss for the first time IR-divergent resonant contributions and highlight an inconsequential inconsistency in the previous literature.

Self-enhanced mobility enables vortex pattern formation in living matter.

Ranging from subcellular organelle biogenesis to embryo development, the formation of self-organized structures is a hallmark of living systems. Whereas the emergence of ordered spatial patterns in biology is often driven by intricate chemical signalling that coordinates cellular behaviour and differentiation1-4, purely physical interactions can drive the formation of regular biological patterns such as crystalline vortex arrays in suspensions of spermatozoa5 and bacteria6. Here we discovered a new route to self-organized pattern formation driven by physical interactions, which creates large-scale regular spatial structures with multiscale ordering. Specifically we found that dense bacterial living matter spontaneously developed a lattice of mesoscale, fast-spinning vortices; these vortices each consisted of around 104-105 motile bacterial cells and were arranged in space at greater than centimetre scale and with apparent hexagonal order, whereas individual cells in the vortices moved in coordinated directions with strong polar and vortical order. Single-cell tracking and numerical simulations suggest that the phenomenon is enabled by self-enhanced mobility in the system-that is, the speed of individual cells increasing with cell-generated collective stresses at a given cell density. Stress-induced mobility enhancement and fluidization is prevalent in dense living matter at various scales of length7-9. Our findings demonstrate that self-enhanced mobility offers a simple physical mechanism for pattern formation in living systems and, more generally, in other active matter systems10 near the boundary of fluid- and solid-like behaviours11-17.

Conditionally integrable PT -symmetric hierarchies and near-Lax pairs of the KdV and KPII equations

Earlier work is generalized to obtain novel conditionally-integrable hierarchies of various PT -symmetric, nonlinear partial differential equations. The Painlevé Test yields the possible integrable cases. These are labeled by the integer n, the order of the dominant pole in the Laurent expansion for the solution. For the PT -symmetric Korteweg–de Vries (KdV) equation which has been considered earlier, further analysis using the extended homogeneous balance technique gives the near-Lax Pair. Next, a PT -Symmetric hierarchy of (2 + 1) Kadomtsev-Petviashvili equations is considered. The Painlevé Test and Invariant Painlevé analysis in (2 + 1) dimensions yield special solutions and Bäcklund Transformations for the integrable cases.

Anisotropic Strain-Tailoring Nonlinear Optical Response in van der Waals NbOI2.

Two-dimensional (2D) NbOI2 demonstrates significant second-harmonic generation (SHG) with a high conversion efficiency. To unlock its full potential in practical applications, it is desirable to modulate the SHG behavior while utilizing the intrinsic lattice anisotropy. Here, we demonstrate direction-specific modulation of the SHG response in NbOI2 by applying anisotropic strain with respect to the intrinsic lattice orientations, where more than 2-fold enhancement in the SHG intensity is achieved under strain along the polar axis. The strain-driven SHG evolution is attributed to the strengthened built-in piezoelectric field (polar axis) and the enlarged Peierls distortions (nonpolar axis). Moreover, we provide quantifications of the correlation between strain and SHG intensity in terms of the susceptibility tensor. Our results demonstrate the effective coupling of orientation-specific strain to the anisotropic SHG response through the intrinsic polar order in 2D nonlinear optical crystals, opening a new paradigm toward the development of functional devices.

Spontaneous Atomic-Scale Polar Skyrmions and Merons on a SrTiO3 (001) Surface: Defect Engineering for Emerging Topological Orders.

The emergence of nontrivial topological order in condensed matter has been attracting a great deal of attention owing to its promising technological applications in novel functional nanodevices. In ferroelectrics, the realization of polar topological order at an ultimately small scale is extremely challenging due to the lack of chiral interaction and the critical size of the ferroelectricity. Here, we break through these limitations and demonstrate that the ultimate atomic-scale polar skyrmion and meron (∼2 nm) can be induced by engineering oxygen vacancies on the SrTiO3 (001) surface based on first-principles calculations. The paraelectric-to-antiferrodistortive phase transition leads to a novel topological transition from skyrmion to meron, indicating phase-topology correlations. We also discuss accumulating and driving polar skyrmions based on the oxygen divacancy model; these results and the recent discovery of defect engineering techniques suggest the possibility of arithmetic operations on topological numbers through the natural self-organization and diffusion features of oxygen vacancies.