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Valleytronics has attracted much attention due to its potential applications in information progress and data storage. In this paper, monolayer Cr2S3 is proven to be a ferromagnetic (FM) semiconductor by using first-principles calculations. Moreover, monolayer Cr2S3 exhibits a perpendicular magnetic anisotropy energy of 30 μeV/f.u. Surprisingly, monolayer Cr2S3 presents spontaneous valley polarization, which means that it will be nonvolatile for data storage. Notably, monolayer Cr2S3 changes to an antiferromagnetic (AFM) state from the original FM state under biaxial tensile strain, and its easy axis will be reorientated from out-of-plane to in-plane when the compressive strain is larger than −2%. Importantly, for AFM monolayer Cr2S3, the valley polarization reversion can be realized by an external electric field along the z direction. In brief, valley polarization has been achieved in both FM and AFM monolayer Cr2S3, which is very rare in other valleytronics research. The present research provides a tantalizing candidate for realizing and manipulating valley and spin physics. [ABSTRACT FROM AUTHOR]

We report the synthesis and experimental studies on the liquid crystalline phase of a homologous series of compounds comprised of strongly asymmetric bent-core banana shaped molecules. Our x-ray diffraction studies clearly indicate that the compounds exhibit a frustrated tilted smectic phase with layer undulated structure. The low value of the dielectric constant as well as switching current measurements indicate the absence of polarization in this layer undulated phase. In spite of the absence of polarization, a planar aligned sample can be transformed irreversibly to a higher birefringent texture on the application of a high electric field. The zero field texture can only be retrieved by heating the sample to the isotropic phase and cooling it subsequently to the mesophase. We propose a double tilted smectic structure having layer undulation to account for the experimental observations with the layer undulation arising due to the leaning of the molecules in the layer. [ABSTRACT FROM AUTHOR]

Second-harmonic generation (SHG), linear electro-optic effect (LEO) and electric-field induced second-harmonic generation (EFISH) are nonlinear optical processes with important applications in optoelectronics and photovoltaics. SHG and LEO are second-order nonlinear optical processes described by second-order susceptibility. Instead, EFISH is a third-order nonlinear optical process described by third-order susceptibility. LEO and EFISH are only observed in the presence of a static electric field. These nonlinear processes are very sensitive to the symmetry of the systems. In particular, LEO is usually observed through a change in the dielectric properties of the material while EFISH can be used to generate a "second harmonic" response in centrosymmetric material. In this work, we present a first-principle formalism to calculate second- and third-order susceptibility for LEO and EFISH. LEO is studied for GaAs semiconductor and compared with the dielectric properties of this material. We also present how it is possible for LEO to include the ionic contribution to the second-order macroscopic susceptibility. Concerning EFISH we present for the first time the theory we developed in the framework of TDDFT to calculate this nonlinear optical process. Our approach permits to obtain an expression for EFISH which does not contain the mathematical divergences in the frequency-dependent second-order susceptibility that caused until now many difficulties for numerical calculations. [ABSTRACT FROM AUTHOR]

We present a theoretical study of the simultaneous effects of ferroelectric nanoparticles and ion impurities on the order parameter of liquid crystals. We have focused on the effect of ion impurities on the ordering behavior and electrical response of a ferroelectric nano-doped liquid crystal near the nematic-isotropic phase transition. In this study, a statistical theory based on the orientational distribution of the nanoparticle dopants is used. We have performed the calculations using the Poisson–Boltzmann equation and a modified Landau-De Gennes model. The total density of free energy of the system is obtained within the framework of this theory, and the changes in the concentration of mobile ions due to the presence of ferroelectric nanoparticles are investigated. It is shown that the screening effect of the ion impurities plays a dominant role in the ordering behavior and electrical response of a ferroelectric nano-doped liquid crystal. The ion generation and the consequent changes are also described in some physical properties of a nano-doped system under an applied electric field. [ABSTRACT FROM AUTHOR]

The electro-optic effect becomes prominent when an electric field is applied across the optic axis of a dielectric material inducing the changes in refractive indices of the medium. Kerr and Pockels cells are massively used as optical switches because of their nonlinear electro-optic character. Potassium di-hydrogen Phosphate (KDP) crystal is a very good electro-optic Pockels material as well as has a good switching behavior in optical and opto-electronic domain. The principle of this electro optic effect can be successfully used to develop optical switch based information processing devices. Transmission co-efficient of the polarized light beam have been modulated in a new way by introducing a multi passing scheme across a electro-optic material. Here transmission co-efficient plays a vital role to examine how much output intensity changes for developing feedback one by one in ascending order. In this paper a novel study for the sizable increase of transmission co-efficient of a KDP crystal for a fixed biasing voltage is reported adopting proper feedback mechanism of light. This paper we also observe an theoretical basis for achieving unit transmission coefficient which minimum amount of voltage require for adopting comparatively many large number of feedback. [ABSTRACT FROM AUTHOR]

Sessile nematic droplets provide a possibility to study the combined effect of anchoring at solid and gas interfaces. The combination of various alignments at the two surfaces and external fields results in a variety of director distribution schemes, ranging from a defect-free, almost homogeneous state to configurations with point-, line- and wall defects. This paper reviews recent results obtained on sessile droplets of uniaxial nematic liquid crystals, such as temperature-controlled anchoring transitions, formation and dynamics of Néel wall type metastable inversion walls in magnetic and/or electric fields. The structures of the recently discovered twist-bend and ferroelectric nematic liquid crystals will also be briefly discussed. [ABSTRACT FROM AUTHOR]

Sessile droplets of a ferroelectric nematic liquid crystalline material were exposed to surface electric fields produced by pyroelectric and photogalvanic (photovoltaic) effects in X-cut iron-doped lithium niobate crystals. The resulting dynamic processes were monitored by polarisation optical (video)microscopy (POM). During heating/cooling cycles, at first, the droplets change their shape from spherical to extended ellipsoidal. Then, they start to move rapidly along the surface electric field, i.e. along the crystal's polar axis (c-axis). During this motion, several droplets merge into running streams (tendrils) extending towards the edges of the top surface area. Finally, practically all liquid crystalline material is transported from the top surface to the side surfaces of the crystal. At stabilised temperatures, laser illumination of the assembly causes dynamic processes that are localised to the illuminated area. Also, in this case, the LC droplets merge into several tendril-like formations that are preferentially oriented along the c-axis of the crystal. The pattern of tendrils fluctuates with time, but it persists as long as the illumination is present. In this case, the LC material is transported between the central and the edge regions of the illuminated area. [ABSTRACT FROM AUTHOR]

Studies of sessile droplets and fluid bridges of a ferroelectric nematic liquid crystal in externally applied electric fields are presented. It is found that above a threshold, the interface of the fluid with air undergoes a fingering instability or ramification, resembling to Rayleigh-type instability observed in charged droplets in electric fields or circular drop-type instabilities observed in ferromagnetic liquids in magnetic field. The frequency dependence of the threshold voltage was determined in various geometries. The nematic director and ferroelectric polarization direction was found to point along the tip of the fingers that appear to repel each other, indicating that the ferroelectric polarization is essentially parallel to the director. The results are interpreted in connection to the Rayleigh and circular drop-type instabilities. [ABSTRACT FROM AUTHOR]

This study has two goals. First, the electric field gradient (EFG) present in the liquid-crystalline phases of ferroelectric FELIX-R&D is determined using NMR spectroscopy of noble gases 21Ne and 131Xe. The 21Ne and 131Xe NMR spectra were recorded over a temperature range, which covers all the mesophases of FELIX-R&D: nematic N*, smectic A, and smectic C*. The spin quantum number of both 21Ne and 131Xe is 3/2. Their electric quadrupole moment interacts with the EFG at the nuclear site, which in liquid-crystalline phases results in the NMR spectra of the triplet structure, instead of a singlet detectable in the isotropic phase. The total EFG experienced by the noble gas nuclei consists of two contributions; one arises from the quadrupole moments of the liquid crystal molecules (external contribution) and the other one from the deformation of the electron distribution of the atoms (deformational contribution). The total EFGs determined from the 131Xe and 21Ne quadrupole splittings are very similar in the nematic and smectic A phases but differ in the smectic C* phase, being about twice larger in the 21Ne case which stems from the larger deformation of the xenon electron cloud than that of neon. For the first time, EFG was determined also in the smectic C* phase applying noble gas NMR spectroscopy. Second, the structure of molecules which, as a mixture, compose the used ferroelectric liquid crystal, FELIX-R&D, is determined by applying a number of various NMR methods and sophisticated spectral analysis. In this part, NMR spectra were recorded from FELIX-R&D/CDCl3 solution. The NMR spectral analysis was divided into four subsystems with over 13 000 000 nonzero intensity transitions. It appeared that FELIX-R&D is composed of three phenyl pyrimidine derivatives and a chiral dopant with fluorine in the asymmetric carbon atom. [ABSTRACT FROM AUTHOR]

• Ferroelectric nematic bridges exposed to electric fields undergo a primary and a secondary interfacial instability. • Experiments and simulations support the requirement of the insulating layers on the electrodes. • Analogies and differences compared to the cases of magnetic and dielectric fluids are presented. • The studied phenomena may give rise to possible new applications in microfluidics, gas sensing and flow control. Recently, an electric field induced interfacial instability of ferroelectric nematic liquid crystals was reported (Sci. Rep. 13:6981 (2023)). It was found that above a threshold, the interface of the fluid with air undergoes a fingering instability or ramification. Here it is shown that by increasing the voltage between the two sides of a ferroelectric liquid bridge, the primary fractal-like ramification is followed by a secondary labyrinthine instability. The instabilities are well distinguishable by their completely different morphologies, and they both emerge sharply at distinct threshold voltages. The critical requirements for the instabilities are presented and the crucial role of the insulating layers on the electrodes is discussed. Experiments and finite element method simulations suggest that the main driving force of the ramification and labyrinthine instabilities is an unexpected electric field component parallel to the electrodes. [ABSTRACT FROM AUTHOR]

In this work, a combined system including FLC high‐speed polarization rotator, liquid crystal polymerizable polarization grating, FLC switchable Dammann Grating is proposed to form tunable diffractive spot matrices and acquire depth information. By adjusting electric field, the grating can be switched between diffractive state showing 4 by 4 optical spots arrays in two areas and non‐diffractive state, respectively. At a low driving voltage of 5V, our approach renders the gratings electrically tunable with a fast response time of 50μs, which has the potential for LiDAR applications. [ABSTRACT FROM AUTHOR]

In order to achieve collinear phase-matched nonlinear optical frequency conversion in cubic crystals, a novel method to induce and modulate the birefringence based on the linear electro-optic effect was studied. Taking terahertz generation with ZnTe and CdTe crystals of the 4 ¯ 3 m point group as an example, an external electric field provided the freedom to realize perfect phase matching (PM) in a wide bandwidth up to 2 THz for difference frequency generation, with monochromatic optical waves at around 800 nm and 1010 nm, respectively. Theoretical simulations showed that such a method helps to extend the terahertz frequency, enhance the conversion efficiency, and alleviate the limitation on the pump wavelength, which is highly favorable for nonlinear optical uses of cubic crystals. Simultaneous wideband terahertz generation pumped by ultrashort laser pulses via optical rectification or difference frequency mixing was also discussed, indicating that an electric field can be used to modulate the PM characteristics without changing the group velocity-matching condition. Tuning the nonlinear interaction by an applied voltage is fast, robust, and convenient compared to other approaches. In addition, the linear electro-optic effect can make the nonlinear crystal a compact and high-speed terahertz amplitude modulator, which has great potential in radar, communication, imaging, etc. [ABSTRACT FROM AUTHOR]

• 4-alcyloxy-2,3-difluorobenzoic acids self-associate as hydrogen-bonded SmC and SmA liquid crystals. • Mixing 4-alcyloxy-2,3-difluorobenzoic acids and 4-octyloxybenzoic acid the stabilizes a supplementary nematic phase. • The nematic phase shows a relaxation at 1.2 MHz frequency and a short response time to electric field in the millisecond range. [ABSTRACT FROM AUTHOR]

We deposited polar-axis-oriented tetragonal and rhombohedral single domain Pb(Zr, Ti)O3 (PZT) films on CaF2(100) substrates by inserting SrRuO3 (SRO)/LaNiO3 and SRO/SrTiO3/TiO2/CeO2 buffer layers. Both PZT films grew epitaxially and had a (001)- and (111)-domain with the remnant polarization and piezoelectric constant comparable to the theoretical values of PZT single crystals having the same compositions. The electro-optic (EO) response of the fabricated PZT films was constant with respect to the DC electric field and increased linearly with an increasing AC electric field, thus representing a typical linear EO response in single domain ferroelectrics. The measured EO coefficients were larger than the value for a single crystal of PbTiO3, i.e., one of the end members of PZT, but smaller than the values reported for polycrystalline and epitaxial PZT films with multiple domains. These findings show that the intrinsic EO effect is enhanced in PZT, which is similar to the enhancement seen in the dielectric and piezoelectric constants. Moreover, most of the reported EO response in PZT films is supported by additional extrinsic contributions. [ABSTRACT FROM AUTHOR]

GaAs‐based semiconductors are highly attractive for diverse nonlinear photonic applications, owing to their non‐centrosymmetric crystal structure and huge nonlinear optical coefficients. Nanostructured semiconductors, for example, nanowires (NWs), offer rich possibilities to tailor nonlinear optical properties and further enhance photonic device performance. In this study, it is demonstrated highly efficient second‐harmonic generation in subwavelength wurtzite (WZ) GaAs NWs, reaching 2.5 × 10−5 W−1, which is about seven times higher than their zincblende counterpart. This enhancement is shown to be predominantly caused by an axial built‐in electric field induced by spontaneous polarization in the WZ lattice via electric field‐induced second‐order nonlinear susceptibility and can be controlled optically and potentially electrically. The findings, therefore, provide an effective strategy for enhancing and manipulating the nonlinear optical response in subwavelength NWs by utilizing lattice engineering. [ABSTRACT FROM AUTHOR]

Ferroelectric liquid crystals remain of interest for display and spatial light modulators because they exhibit significantly faster optical response times than nematics. However, smectic layers are sensitive to shock-induced flow and are usually permanently displaced once a well-aligned sample is disrupted, rendering such devices inoperable. We introduce a vertical alignment geometry combined with a surface-relief grating to control both the smectic layer and director orientations. This mode undergoes "self-healing" of the smectic layers after disruption by shock-induced flow. Sub-millisecond switching between optically distinct states is demonstrated using in-plane electric fields. Self-healing occurs within a second after being disrupted by shock, wherein both the layer and director realign without additional external stimulus. The route to material improvements for optimised devices is discussed, promising faster spatial light modulators for high-speed adaptive optics, micro-displays for virtual/augmented reality and telecommunications with inherent shock stability. Ferroelectric liquid crystals (FLCs) have faster optical response times than nematic crystals, but they are also less robust to external shock. Here the authors develop an FLC geometry that reduces the sensitivity to external disruption through self-healing, making them more stable for applications. [ABSTRACT FROM AUTHOR]

Comments and the work presented in this paper aim at initiating discussion within the liquid crystalline community about the nature of different biaxial phases and their switching mechanisms. The mechanisms have the potential for applications in switching devices for displays and photonics. Claire Meyer et. al. interestingly report recently a fast Freedericksz-like transition of the secondary director in the biaxial Smectic Ab phase of a mixture of two compounds. Fast switching in liquid crystals occurs through a coupling of the biaxiality with the electric field. To realise this potential, one of the major goals of the liquid crystal community had been to discover biaxial nematic liquid crystals. In a biaxial liquid crystalline phase, the refractive indices along the three orthogonal axes are all different [n11≠ n22 ≠ n33] as opposed to these being different only along the two orthogonal directions n11 ≠ n22 = n33 in uniaxial nematics. In this notation 1, 2 and 3 are the three orthogonal axes that coincide with the major and the two minor directors. The biaxial nematic phase has been elusive for over half a Century. It has therefore proven to be almost impossible to meet the goal of achieving fast switching using biaxial nematics. Ferroelectric and antiferroelectric liquid crystals were discovered in 1975 and 1989 by R. Meyer in the USA and Atsuo Fukuda in Japan, respectively, for fast switching. These have been used in devices for niche but limited high-resolution applications as the devices using these liquid crystals suffered not only from achieving proper alignment at surfaces but also showed poor recovery of alignment following repeated cycles of switching. [ABSTRACT FROM AUTHOR]

The fringe field effect (FFE) is one of the biggest bottlenecks for the display, and the photonic industry limiting the pixel per inch (PPI) to ~450. The modern applications such as AR/VR headsets and photonic elements such as wavelength selective switches required significantly higher PPI panel. Despite the rigorous research efforts, conventional LCs still show serious FFE, and therefore, hinder the progress of high PPI display and photonic elements. In this article, we studied FFE in the deformed helix ferroelectric liquid crystals (DHFLCs) and found that the subwavelength pitch of the DHFLCs is critically important to suppress the FFE. These DHFLCs show no FFE, for the electric field parallel to the FLC helix, however, we have observed some FFE for the electric field perpendicular to the FLC helix. Additionally, we have found that the high-frequency driving further suppresses the FFE. Later, we deployed DHFLCs to diffraction grating and display to confirm our findings. The proposed DHFLCs with subwavelength pitch can support pixel density up to 4233 PPI for displays, and up to 12,700 PPI for monochromatic photonic devices. Thus, the fast switchable DHFLCs with subwavelength pitch pave the way for the high-pixel density display and photonic devices. [ABSTRACT FROM AUTHOR]

We developed a theory for the statistical mechanics of nanoparticles doped in ferroelectric liquid crystals (FLC). The presence of nanoparticles in FLC medium creates strong local fields that produce large alignment effects over the distribution of the nanosuspensions. Considering these local field effects, we presented a modified Landau free energy to calculate the electro-optic properties of the system. Then, we investigated the response of the nanoparticles doped FLC to an applied electric field. The variations in the polarization and the tilt angle show marked differences with the pure FLC medium. The rotational viscosity of the system is also calculated with its possible variation in temperature and applied field. Then, we conjectured on the possibility of shift in transition temperature, which is supposed to be induced by an electrostatic interaction between the nanoparticles and the liquid crystal molecules. Finally, strong experimental evidence is presented in favor of our results emerged from this theoretical model. [ABSTRACT FROM AUTHOR]

Domain switching is one of the essential contributions for strain in ferroelectric materials. In this work, we utilize anisotropic composition gradients (CGs) to induce anisotropic orientation of both defects and spontaneous dipoles, aiming to enhance the contribution of domain switching on strain in KTa 1– x Nb x O 3 single crystal. In this way, a remarkable improvement (over 60%) of strain is obtained in KTa 0.58 Nb 0.42 O 3 single crystal along the smallest CG direction, achieving a large unipolar strain, i.e. 0.29%, at low driving electric field 10 kV cm–1. It is attributed to the preferred orientation of both defects and spontaneous dipoles along the largest CG directions, then improving the contribution of domain switching on strain along the smallest CG direction. Particularly, owing to the existence of E in as recoverable forces caused by both flexoelectric fields and defects pinning effect, KTN show nearly zero remnant strain (s rem) along with the small CG directions, corresponding to the double P-E loops. Moreover, the V–PFM images confirm that CGs can influence the microdomain structures. Thus, designing special anisotropic CGs materials is expected to be a novel method to improve the strain properties and a potential way to flexibly design next-generation anisotropic piezoelectric materials. Composition Gradients (CGs) can significantly improve the contribution of domain switching on strain by inducing preferred orientation of spontaneous polarization and defect dipoles. It provides a novel method to design graded crystals to achieve strain properties enhancements. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Functional nanocomposites are designed via doping ferroelectric liquid crystal (FLC) matrix by 0.03wt% and 0.1wt% of functionalised multiwall carbon nanotubes (MWCNTs). Mesomorphic, optical, thermo-optic and electro-optic behaviour of resulting nanocomposites have been studied in the ~5μm thick cells. Effect of applied voltage on the mesomorphic and electro-optic behaviour of ferroelectric liquid crystal has been established. Interestingly, FLC material demonstrates electrically switchable birefringence colours viz. yellow, reddish, violet and green colour, under applied electric field at different temperatures. No considerable perturbation of FLC smectic order has been observed with doping of MWCNTs. However, the MWCNT doping strongly modifies the optical contrast, birefringence, transmission and contrast ratio of the FLC material. The most significant results are obtained for nanocomposite with 0.03wt% MWCNTs concentration. Doping by MWCNTs leads to the generation of new colours in the nanocomposite systems and also effectively reduce the driving voltage for the colour appearance. For the designed nanocomposites, a decrease in the spontaneous polarisation and fastening of the switching time has been detected. Such electrically switchable birefringent MWCNTs/FLC nanocomposites can be effectively utilised for practical applications in the field-sequential colour displays, FLC switches, optoelectronic and photonic devices. [ABSTRACT FROM AUTHOR]

Electro-optical switching and the liquid crystal (LC) director distribution are studied in spatially periodic electric field for vertically aligned LC with negative dielectric anisotropy. Two electro-optical switching modes characterised by different switching times are observed. These modes are well distinguished optically by choosing proper geometry for the polarisers axes orientation. One of these modes is significantly faster as compared to the other. The fast switching is explained in terms of localised near-to-surface director reorientation. The 3D-numerical simulation shows very good agreement with the experiment: it points out the existence of the disclination lines and field-stabilised walls responsible for the localised director field switching and its relaxation. Possibilities of enhancing the fast mode for high-speed light modulators are discussed. [ABSTRACT FROM AUTHOR]

We study a nanocomposite consisting of a ferroelectric liquid crystal and a magnetic nanoparticle in order to explore the possibility of using it as a magnetic resonant imaging contrast agent which will measure a field of 20 V/m. To achieve this we use the ferroic properties exhibited by the nanocomposite. We used the ferroelectric liquid crystal 2-(4-((2-fluorooctyl)oxy)phenyl)-5-(octyloxy)pyrimidine mixed with FeCo nanoparticles nominally 2–3 nm in diameter in concentrations of 0.56, 4.3 and 10.8 wt%. The 10.8 wt% sample was chosen for our study because the nanoparticles acted as a lubricant for the ferroelectric liquid crystal. This concentration yields nanoparticle clusters in about 5 − 10 μm diameter spherulites. An electric field as low as 5V/cm is enough to turn and realign the spherulites where the particles are contained. We estimate the value of the magnetic in a spehrulite and associate it to the number of spherulites aligned as a function of electric field. We find thus that we can achieve low electric fields. [ABSTRACT FROM AUTHOR]

New areas of application in the realms of fast phase modulators are stimulating fundamental studies in ferroelectric liquid crystalline materials. Investigation of temperature effect on light transmittance in vertically aligned deformed helix ferroelectric liquid crystal cell is the focus of our study. A fairly linear Kerr constant temperature dependence for two ferroelectric liquid crystal mixtures was analyzed by using linear regression analysis. The key result of this paper represents light transmittance dependencies as a function of squared electric field for a certain temperature range. We also report that strongly pronounced Kerr constant temperature dependence results in several temperatures with 2 π and higher phase modulation for the given electric field. The physics of change in light transmission plots has been analyzed. [ABSTRACT FROM AUTHOR]

Abstract In this paper, we present a novel optical power splitter having an arbitrary split-ratio that can be tuned over a wide range by employing relatively low voltage levels. It is based on a slotted ring resonator. A 120 nm electro-optic polymer-filled slot is created throughout the circumference of the ring. The hybrid ring resonator is made to work between the full and off resonance states, allowing it to work as a power splitter. This is done by changing the refractive index of the electro-optic polymer inside the slot by the application of an external electric field. The splitter combines the electro-optic functionality of the polymer with the high index contrast of the silicon, resulting in a low tuning voltage power splitter. Over a small voltage range of 0–1 V, it is possible to change the split-ratio of this splitter from 0.031–16.738, making it 10 times better than other competing designs. In addition, it takes less than 500 ps to reconfigure the splitter. [ABSTRACT FROM AUTHOR]

Electro-optical and spectral studies of isotropic photonic crystal fibre (PCF) infiltrated with photo-aligned ferroelectric liquid crystal (FLC) under influence of external electric field are described. Desired alignment of FLC molecules is provided by generation of photo-aligning surface on the inner side of PCF structure. Propagation of light spectrum, as well as light attenuation have been investigated in details. Moreover, the electro-optical response times were measured and analysed. [ABSTRACT FROM AUTHOR]

The recently discovered ferroelectric nematic liquid crystals have been reported to exhibit very large dielectric permittivity values. Here, we report a systematic investigation of the dielectric behavior of a prototypical ferroelectric nematogen by varying the thickness of the parallel capacitor measuring cell. While in the non-polar high temperature nematic phase results show only slight differences due to slight variations of the alignment, the measured permittivity values in the ferroelectric nematic phase show a linear dependence on the cell thickness. It is also shown that the characteristic relaxation frequency decreases inversely proportionally to the thickness. The results are discussed in terms of three different available models based on different underlying mechanisms, accounting for cancellation of the probe electric fields by polarization reorientation or by ionic charges, or based on a recently proposed continuous phenomenological model. • Measured dielectric permittivity values show a clear dependence on the thickness of the measuring parallel plate capacitor. • The characteristic relaxation frequency is inversely proportional to the sample thickness. • The obtained data have been analyzed in terms of three different models based on distinct physical mechanisms. [ABSTRACT FROM AUTHOR]

At high transmembrane electric field, a voltage sensitive ion channel is an insulator; when the field is critically reduced, it becomes a conductor of selected ions. The Channel Activation by Electrostatic Repulsion (CAbER) hypothesis proposes that an ordered polarization field of induced dipoles at the high electric field magnitude of the excitable state is overcome by thermal disorder at a critical depolarization. Increased repulsions between positive charges in the S4 segments cause an allosteric transition in which these segments expand and separate in a chiral proteinquake. The increased space allows the P segments to refold and the ion-semiconducting S5 and S6 segments to relax and expand outward in a breathing mode. Stripped permeant ions enter widened hydrogen bonds in the core helices of these segments. Driven by concentration differences and the electric field, the ions hop along transient pathways across the channel, appearing as fractal, stochastic bursts of single-channel currents. To support order amid thermal fluctuations, an object must be of a minimum size. The critical role of an ion channel's size suggests that the evolution of Metazoa became possible only after its DNA had grown enough to code for proteins larger than the correlation length. [Display omitted] • Branched sidechains are the link between depolarization and S4 movements. • Increased repulsions between positive charges drive the S4 segments apart. • As the pore-forming domain expands, its hydrogen bonds widen to become ion sites. • Permeant ions form fractal, stochastic bursts of current across the membrane. • Evolutionary gene doubling gave rise to large ordered phases of animal ion channels. [ABSTRACT FROM AUTHOR]

It is well established that incorporation of nanoparticles (NPs) in the structure of ferroelectric liquid crystals (FLCs) leads to a decrease in their electrooptic response time. Several approaches have been suggested to explain this effect (decrease in rotational viscosity of FLCs, ions enhanced localised electric field, dipole-dipole interaction among NPs and FLC molecules, FLC ordering). In this article, we will report the role of the voltage divider formed by the structural elements of a FLC cell based on ferroelectric liquid crystal/gold nanospheres (FLC/GNSs) dispersion in enhancement of the switching time. Using the impedance spectroscopic measurements, it was demonstrated that the dispersing of GNSs leads to the increase in the voltage drop on FLC/GNSs layer in comparison with the pristine FLC one. Consequently, the electrooptic response time of the FLC/GNSs cell is faster than that of the pristine one. However, the rotational viscosity of the FLC does not depend on the presence of the GNSs. [ABSTRACT FROM AUTHOR]

Recent theoretical developments regarding the understanding of weakly chaotic transients in ferroelectric liquid crystals (FLCs), induced by electric field, are studied in terms of the interaction with magnetic field. Our research is related with the nonlinear dynamical system represented by a thin film of surface-stabilized FLC in smectic C* phase, and subjected by the swinging magnetic field. The computation of the Lyapunov exponents from the dynamic equation for the director field reveals that the director dynamics exhibits limit cycle, hyperchaotic attractor and strange attractor behavior in the dissipative nonlinear media. The transients between director’s phase space trajectories can be handled by the magnetic field parameters. The fundamental understanding of the director dynamics may have a valuable contribution to the applications of thin liquid crystal films. [ABSTRACT FROM AUTHOR]

Starting from a Langevin formulation of a thermally perturbed nonlinear elastic model of the ferroelectric smectic-C * (SmC*) liquid crystals in the presence of an electric field, this article characterizes the hitherto unexplored dynamical phase transition from a thermo-electrically forced ferroelectric SmC * phase to a chiral nematic liquid crystalline phase and vice versa. The theoretical analysis is based on a combination of dynamic renormalization (DRG) and numerical simulation of the emergent model. While the DRG architecture predicts a generic transition to the Kardar-Parisi-Zhang (KPZ) universality class at dynamic equilibrium, in agreement with recent experiments, the numerical simulations of the model show simultaneous existence of two phases, one a subdiffusive (SD) phase characterized by a dynamical exponent value of 1, and the other a KPZ phase, characterized by a dynamical exponent value of 1.5. The SD phase flows over to the KPZ phase with increased external forcing, offering a new universality paradigm, hitherto unexplored in the context of ferroelectric liquid crystals. [ABSTRACT FROM AUTHOR]

In this work, we have considered the application of thermodynamic model, as developed by us, to investigate, under electric field, the variation of relative temperature(T − T c ), where T c represents Sm C* − Sm A* transition temperature, and spontaneous polarization with tilt angle of Sm C* phase near Sm A* − Sm C* phase transition in surface stabilized ferroelectric liquid crystals (SSFLCs). Based on the concept of Landau-de-Gennes formalism, the free-energy density of the system has been written as an expansion series in powers of relevant order parameters and their coupling terms. Adopting usual method, we have evaluated the values of spontaneous polarization ( P s ) and relative temperature (T − T c ) as a function of tilt angle for seven SSFLCs materials. In case of materials exhibiting second-order transition a wide temperature variation in the tilt angle has clearly been observed. For materials showings first-order transition, the transition enthalpy has been found to be directly related to the Landu coefficient (b) associated with cubic power of orientational order parameter. We have found a close agreement between theory and experiment. [ABSTRACT FROM AUTHOR]

In this article, a ferroelectric liquid crystal (FLC) dammann grating (DG) is demonstrated based on the patterned photoalignment technology. By applying low electric field (10 V) on the FLC DG, the grating can switch between a diffractive state with 7 × 7 optical spots array and a non-diffractive state, depending on the polarity of electric field. The FLC DG shows very fast switching speed with switching on time and off time to be only 81 s and 59 s respectively. Comparing with other fast LC DGs such as the ones based on blue phase LC or dual-frequency LC, the switching speed of the proposed FLC DG is about one order faster, which provides great potential and perspective for the FLC DG to be applied in a broad range of optical applications such as optical communication and beam shaping. [ABSTRACT FROM AUTHOR]

In this contribution we report a theoretical study of relaxation processes in surface-stabilized ferroelectric liquid crystals with spontaneous polarization. The influence of pulsed electric field on the behavior of ferroelectric liquid crystal in the SmC* phase, which is placed in a thin cell with strong anchoring of SmC* molecules with the boundary substrate, is studied. In the vicinity of the substrate interface, temporal dependence of the azimuthal motion of the director induced by electric field is obtained. The response to the external distortion of ferroelectric liquid crystal confined between two microstructured substrates is the occurrence of periodic temporal formation of solitons connected with the distortion of the director field n in the sample bulk. The interplay between microstructured substrates and director distribution of the ferroelectric SmC* phase is explained by the Frenkel-Kontorova model for a chain of atoms, but adapted for the continuum problem. [ABSTRACT FROM AUTHOR]

Surface stabilized ferroelectric liquid crystal (SSFLC) doped with ferroelectric nanoparticles shows interesting polarization and orientational behavior in external fields. In this work we study the behavior of a nanodoped SSFLC subjected simultaneously to electric and magnetic fields. The threshold fields and maximum deviation of the polarization vectors for a pure and nanodoped system are calculated and the strong influence of spontaneous polarization on magnetic threshold field is revealed as well as on electric field. We assume that the smectic layers consist of uniform planes with a fixed orientation and the system is free from dislocation of constant layer thickness due to nanoparticles. Comparing the obtained results for a nanodoped one with the transition behavior in a pure cell shows the significant influences of nano dispersions on ordering behavior even at low concentrations. The results exhibit the dependence of magnetic threshold field on the presence of ferroelectric nanoparticles and the spontaneous polarization as well as some other material and external parameters. The boundaries for the stability of the uniform configuration of a pure and nanodoped SSFLC system are determined. It is also found that for a SSFLC structure, beyond a critical thickness between the boundary plates of the cell, the Fredericks threshold fields would not be sensitive to the cell thickness. [ABSTRACT FROM AUTHOR]

Influence of ferroelectric BaTiO3particles on dielectric and electro-optic properties of liquid crystals (LC) 5CB and H37 has been investigated. It has been shown that the presence of particles decreases the clearing temperature, increases dielectric permittivity and losses, changes the Freedericksz transition voltage and switching times. A rise time of the BaTiO3-5CB colloid improved while a decay time worsened in comparison with the pure 5CB at all applied voltages. The inverse trends were observed for the H37 matrix. Experimental results are explained by appearance of local electric fields near the polarized ferroelectric particles at application of external electric field. [ABSTRACT FROM AUTHOR]

Dielectric behaviour of a new ferroelectric liquid crystal (CLF08) having large spontaneous polarisation (120 nC/cm2at 110 Hz), short pitch and high purity, is studied in the frequency range 5 Hz to 1 MHz, in the smectic C* and smectic A phases using a 7-micron-thick cell in planar alignment. Dielectric permittivity, polarisation and optical measurements are investigated that shows complex ferroelectric behaviour. These experiments evidence the Goldstone and Soft mode relaxations far from the SmC*to SmA transition. The density of dechiralization lines is observed under polarised light microscope. Its behaviour under electric field exhibits a remarkable accordance with the dielectric response. These results are discussed in connection with a possible onset of ferrielectricity in the dechiralization lines system. [ABSTRACT FROM AUTHOR]

Preliminary studies of photonic crystal fibers (PCFs) partially infiltrated with photo-aligned ferroelectric liquid crystals (FLCs) under the influence of external electric field are reported. The proper alignment of the FLC molecules is achieved by generating a photo-aligning layer on the inner side of the PCF microcavities. The sulfonic azo dye, which is used as an alignment layer, offers a variable anchoring energy depending on the irradiation energy, and thus, a good control on the FLC alignment inside microchannels is possible. Moreover, a state of polarization of the light being guided inside the PCF infiltrated selectively with FLC changes under the influence of external electric field. [ABSTRACT FROM AUTHOR]

A systematic study highlighting the effect of cadmium selenide quantum dots (CdSe QDs) with varying concentrations of 0.05, 0.10 and 1.0 wt% doping on the electrooptical and dielectric parameters of ferroelectric liquid crystal (FLC) is presented. No considerable change is observed in phase transition temperature and tilt angle with CdSe QDs doping at lower and higher dopant level. Substantial enhancement of localised electric field at higher doping level (1.0 wt%) of CdSe QDs manifested the ≈48% reduction in the switching response of FLC nanocolloids at 30°C. Reduction in the spontaneous polarisation, dielectric constant and absorption strength could be attributed to the antiparallel correlation among dopant and matrix molecules, ion capturing in the capping additive layer and enhancement of the rotational viscosity of the nanocolloids, respectively. Goldstone mode relaxation frequency is found to be decreased with doping up to 0.10 wt% concentration and showed reverse effect at higher QDs concentration. QDs doping effect on the photoluminescence intensity is also discussed. [ABSTRACT FROM PUBLISHER]

We present the characterization and dielectric spectroscopic investigations of a ferroelectric liquid crystal (FLC) material, namely KCFLC 10S. We experimentally demonstrate the observation of a low frequency dielectric relaxation mode along with Goldstone mode in the smectic C* phase of the FLC material under investigation. The behavior of low frequency dielectric relaxation mode has been systematically studied with temperature and applied bias field. The relaxation frequency of the low frequency dielectric relaxation has been found to be shifted toward the higher frequency side with an increase in temperature and field strength. This shift has been attributed to the single particle diffusion of fast ions. Further investigations on electrical conductivity (σ) with frequency at different electric field strengths revealed a Schottky-type of charge injection at electrode even under a small DC bias. The studies carried out in the present paper would be helpful to provide ideas for designing and developing advanced liquid crystal materials. [ABSTRACT FROM AUTHOR]

Abstract: The present work presents, for the first time, the dynamic evolution of the hysteresis loops R(V), specifically based onto the total retardance polarimetric parameter R(t) extracted from the Mueller Matrix (MM) of Twisted Ferro-electric Liquid Crystal (TwFLC) samples. This evolution is given for increased exposure time T exp to a rectangular periodic electric field E app preliminary applied to the sample, before performing the polarimetric measurements. The Mueller Matrix formalism used is found as a relevant non-destructive and non invasive full-optical method to characterize and to monitor the Twisted Ferro-electric Liquid Crystal cell dynamic behaviour under external applied electric field, before reaching the so-called stripes regime. [Copyright &y& Elsevier]

We focus on vertical alignment ferroelectric liquid crystal (FLC) cells fabricated without the rubbing technique to realize FLC displays having high contrast ratio. In this study, we research the conditions for the fabrication of uniformly vertical alignment FLC cells in terms of the tilt angle of FLC and the anchoring strength of alignment film materials. As a result, the uniformly vertical alignment of FLC can be obtained in the case of the small tilt angle and the strong anchoring strength. Furthermore, we investigate the effect of the application of electric field on the vertical alignment. [ABSTRACT FROM PUBLISHER]

In this article, polar columnar liquid crystals are reviewed. After introducing conventional ferroelectric liquid crystals such as smectic C* phases, bent-core smectic polar phases and chiral discotic phases, we stress that the polarisation direction existing in thexyplane (layer plane) is a common feature. Extensive attempts to realise polar columnar structures with the polarisation along thezaxis (Ising type) are reviewed. Although some of them have a long life of polar order after turning off an electric field, a genuine columnar ferroelectric liquid crystal with Ising polarisation has not been discovered until quite recently. Finally, we describe the details of the process towards the discovery, structural features, physical properties and possible applications of this novel material. [ABSTRACT FROM AUTHOR]

We propose a new theoretical approach for description of the equilibrium and bistable states of ferroelectric liquid crystal. A sample of ferroelectric liquid crystal is considered in the ''bookshelf '' geometry under the influence of electric field. Continuumand perturbation theories are used in order to establish the relation between the scale coefficients in the expansion for the azimuthal angle. The equilibrium states of ferroelectric SmC* are determined in the framework of the catastrophe theory. [ABSTRACT FROM AUTHOR]

The SmA*–SmC* phase transition was studied by measuring the temperature and electric field dependences of the optical tilt angle, the electric polarisation and the dielectric spectra collected in a wide frequency range. Critical behaviour of the phase transition was analysed by varying the length of the fluorinated part of the alkyl terminal chain and by differing fluorine substitution in the terphenyl core. Both tilt and polarisation show tricritical mean-field behaviour for all homologues withn > 2. Almost all coefficients that describe the SmA*–SmC* transition in the frame of the Landau theory were derived for homologue series. Double fluorine substitution in the central ring of the core seems to promote the ‘de Vries'-type smectic A*–C* phase transition with a little layer shrinkage. These well correspond with the lower tilt angle and smaller changes of the birefringence at the phase transition compared to the other homologues. [ABSTRACT FROM AUTHOR]

We study both theoretically and experimentally the electro-optical properties of vertically aligned deformed helix ferroelectric liquid crystals (VADHFLC) with subwavelength pitch that are governed by the electrically induced optical biaxiality of the smectic helical structure. The key theoretical result is that the principal refractive indices of homogenized VADHFLC cells exhibit the quadratic nonlinearity and such behavior might be interpreted as an orientational Kerr effect caused by the electric-field-induced orientational distortions of the FLC helix. In our experiments, it has been observed that, for sufficiently weak electric fields, the magnitude of biaxiality is proportional to the square of electric field in good agreement with our theoretical results for the effective dielectric tensor of VADHFLCs. Under certain conditions, the 2n phase modulation of light, which is caused by one of the induced refractive indices, is observed without changes in ellipticity of incident light. [ABSTRACT FROM AUTHOR]

We propose a reliable vertical configuration of a deformed-helix ferroelectric liquid crystal (DHFLC) mode in a transverse electrode structure by introducing reactive mesogens (RMs) into the DHFLC material. Polymerized RMs remember the direction of the DHFLC molecules in the absence of an applied voltage and suppress the bending and breaking of the smectic layer under a strong electric field. In this DHFLC mode with polymerized RMs, reliable switching characteristics are obtained in the vertical configuration. [ABSTRACT FROM AUTHOR]

Optical second-harmonic generation (SHG) has been studied in a trimer smectic C liquid crystal especially designed for nonlinear optical applications. The molecule has a long conjugated donor-acceptor unit that transversally links three parallel rod-shaped moieties. A strong SHG signal has been observed at a fundamental wavelength of 1369 nm even in the presence of the spontaneous helicoidal structure of the smectic C" phase. This unusual behavior has been interpreted as due to the existence of phase matching, in which the wave vector mismatch is compensated by the wave vector of the helix. This point has been confirmed by the study of the SHG intensity versus sample thickness and light polarization characteristics. The main coefficient of the second-order susceptibility tensor of the material has been estimated to be d22 = 28 pm/V. [ABSTRACT FROM AUTHOR]

The present work deals with the dielectric behaviour of a ferroelectric liquid crystal (FLC) dimer. Small values of relative permittivity and dielectric loss for the FLC dimer have been observed. The soft mode at high frequency has been observed near the smectic A-chiral smectic C (SmA−SmC*) transition temperature with a very small value of relaxation strength, which becomes insignificant at higher temperatures in the SmA phase due to intramolecular reorientation. The goldstone mode has not been detected for the complete SmC* phase of the FLC dimer because of the small value of spontaneous polarisation at low applied electric field. The observed dielectric response is attributed to the bulky cholesteryl ester segment. The low value of the relative permittivity and dielectric loss suggests that it may be applicable in spatial light modulators and signal processing if it gives the high electro-optical response at low electric field with suitable doping. [ABSTRACT FROM AUTHOR]

Mixtures of two proprietary low molar mass organosiloxane liquid crystals were studied in order to improve their alignment and optimize their electro-optic properties for telecommunication applications. Over a certain concentration range, mixtures exhibited an isotropic-chiral smectic A-chiral smectic C (Iso-SmA*-SmC*) phase sequence leading to exceptionally good alignment. At room temperature, the spontaneous polarization of these samples was reduced from 225 nC cm-2 in the pure SmC* liquid crystal to as low as 75 nC cm-2 in the mixture. Within this concentration range, the ferroelectric tilt angle could be varied between 35° and 15° , while the rise time decreased by 69.4%. The rise times were <;45 μs for moderate electric fields of ±10 V μm-1 in the SmC* phase and ∼4 μs, independent of electric field, in the SmA* phase. At λ = 1550 nm, these mixtures exhibited very large extinction ratios of ~60 dB for binary switching in the SmC* phase and ~55 dB continuous variable attenuation in the SmA* phase. [ABSTRACT FROM PUBLISHER]