Ordinary Crystals Research Articles

Comparative studies on the nature and kinetics of phase transitions in plastic crystals: Hydrogen-bonded adamantane derivatives

In this paper, the results of thermal, structural, and spectroscopic studies on 3-amino-1-adamantanol (3-NH2-1-OH-ADM) were discussed with those recently published for 1-hydroxyl and 1-amine derivatives of adamantane (1-OH-ADM, 1-NH2-ADM). Calorimetric measurements showed that the examined compound, like 1-NH2-ADM, is characterized by multiple thermal events in the thermogram measured on heating and cooling. Further X-ray diffraction, Fourier-transform infrared, and Raman spectroscopy investigations suggested that two of them correspond to the transition from the ordinary crystal (OC) to the plastic crystal (PC) phase I and the transition between two PC phases (PC(I) and PC(II)), while the third subtle one is rather not related to a phase transition. Interestingly, ambient pressure dielectric studies performed during heating and cooling cycles revealed changes in the imaginary and real parts of the complex dielectric permittivity at temperatures close to the temperatures of phase transitions detected by the calorimetry. Such behavior resembled that reported for 1-NH2-ADM. Finally, isothermal time-dependent dielectric and infrared studies, supported by the analysis of asynchronous 2D-IR correlation spectra, indicated that the first endothermic peak, visible in the thermogram of 3-NH2-1-OH-ADM over an enormously large temperature interval and related to the OC-PC(I) phase transition, similarly to the one, assigned to the PC(I)-PC(II) transition in 1-NH2-ADM, has a character of the kinetic process. Importantly, during the annealing of 3-NH2-1-OH-ADM at T = 328–343 K, we observed a clear change in the dc-conductivity as well as intramolecular dynamics related to the vibrations of CH, NH2, and OH moieties that occur at different rates.

Surface-induced water crystallisation driven by precursors formed in negative pressure regions

Ice nucleation is a crucial process in nature and industries; however, the role of the free surface of water in this process remains unclear. To address this, we investigate the microscopic freezing process using brute-force molecular dynamics simulations. We discover that the free surface assists ice nucleation through an unexpected mechanism. The surface-induced negative pressure enhances the formation of local structures with a ring topology characteristic of Ice 0-like symmetry, promoting ice nucleation despite the symmetry differing from ordinary ice crystals. Unlike substrate-induced nucleation via water-solid interactions that occurs directly on the surface, this negative-pressure-induced mechanism promotes ice nucleation slightly inward the surface. Our findings provide a molecular-level understanding of the mechanism and pathway behind free-surface-induced ice formation, resolving the longstanding debate. The implications of our discoveries are of substantial importance in areas such as cloud formation, food technology, and other fields where ice nucleation plays a pivotal role.

Second-harmonic generation of ultrashort pulses in refractive index linearly modulating quantum dot structure

While other works use segments of nonlinear crystal to compensate for walk-off, this work utilizes a quantum dot (QD) nanostructure for such compensation. Such nanocrystal structures allow two benefits: the high nonlinear susceptibility in these nanocrystals and the high surface density of QDs in the structure. Good results are obtained for pre-chirping and modulation parameters. The results are computed at 10 and 100 kV/cm applied electric fields. Compared to ordinary nonlinear crystals, the pulse width, intensity, and efficiency of the second harmonic (SH) pulse are all higher in QD nanocrystals, even with a low electric field applied. Higher applied fields give higher results.

Molecular shape, elastic constants and spontaneous twist in chiral and achiral nematics: insights from a generalised Maier–Saupe framework

ABSTRACT Ordinary nematic liquid crystals have a uniform director field as ground state. However, there are relevant examples of spontaneously twisted nematic states, not only in chiral, but also in achiral materials. Different twist configurations can be found, with the director modulation along the twist axis, as in the cholesteric and in the twist-bend nematic phase, or perpendicular to it, as in blue phases and in skyrmion structures. Here, we develop a generalised Maier–Saupe theory to calculate the thermodynamic and elastic properties, included saddle-splay, of nematics made of particles whose shape can be described as a distorted rod. This turns out to be a powerful approach for screening the relation between the molecular shape and the formation of modulated nematic phases. Application to the paradigmatic models of banana-shaped and helical particles allows us to identify the role of distinct shape features, such as curvature and chirality, and the distinct mechanisms by which these promote twisted configurations.

Parity-time imbalance induced by balanced gain and loss medium in non-Hermitian photonic crystals

Photonic crystals, including gain and loss materials, show numerous intriguing features than the ordinary photonic crystals. In this work, using the full wave simulation, we numerically investigate the photonic crystals with gain and loss which are satisfying the parity-time (PT) symmetry condition to reveal the effect of PT symmetry on the optical properties of photonic crystals, including the exceptional point, distribution of electromagnetic fields and edge states. This work reveals a novel mechanism of coexistence and competition between topological states and non-Hermiticity in all-dielectric photonic crystals and provides an innovative understanding of non-Hermiticity in topological photonic systems.

GenIce-core: Efficient algorithm for generation of hydrogen-disordered ice structures.

Ice is different from ordinary crystals because it contains randomness, which means that statistical treatment based on ensemble averaging is essential. Ice structures are constrained by topological rules known as the ice rules, which give them unique anomalous properties. These properties become more apparent when the system size is large. For this reason, there is a need to produce a large number of sufficiently large crystals that are homogeneously random and satisfy the ice rules. We have developed an algorithm to quickly generate ice structures containing ions and defects. This algorithm is provided as an independent software module that can be incorporated into crystal structure generation software. By doing so, it becomes possible to simulate ice crystals on a previously impossible scale.

Evaluation of polar alignment structure and surface anchoring energy in ferroelectric nematic liquid crystals by renormalized transmission spectroscopic ellipsometry

It is essential to estimate the surface polar anchoring energy in order to discuss the interfacial orientation of ferroelectric nematic liquid crystals. In this study, we accurately estimated the twist angle of a π -twist cell with an antiparallel rubbing manner, by means of renormalized transmission spectroscopic ellipsometry, which has a great deal of experience in measuring the twist angle of ordinary nematic liquid crystals. We also succeeded in estimating the reduced polar anchoring energy from the essential equation derived from the simplified torque balance equation. It is assumed that the reduced surface polar anchoring energy is on the order of 102.

Ionic plastic crystals and ionic liquids containing quaternary cations with alkenyl substituents: chemical phase transformations by bromine vapor

Quaternary ammonium salts with vinyl or allyl substituents were synthesized, which underwent bromine addition reactions under bromine vapor, resulting in transformations between ionic plastic crystals, ionic liquids, and ordinary ionic crystals.

Splay-induced order in systems of hard tapers.

The main objective of this work is to clarify the role that taper-shaped elongated molecules, i.e., molecules with one end wider than the other, can play in stabilizing orientational order. The focus is exclusively on entropy-driven self-organization induced by purely excluded volume interactions. Drawing an analogy to RM734 (4-[(4-nitrophenoxy)carbonyl]phenyl-2,4-dimethoxybenzoate), which is known to stabilize ferroelectric nematic (N_{F}) and nematic splay (N_{S}) phases, and assuming that molecular biaxiality is of secondary importance, we consider monodisperse systems composed of hard molecules. Each molecule is modeled using six collinear tangent spheres with linearly decreasing diameters. Through hard-particle, constant-pressure Monte Carlo simulations, we study the emergent phases as functions of the ratio between the smallest and largest diameters of the spheres (denoted as d) and the packing fraction (η). To analyze global and local molecular orderings, we examine molecular configurations in terms of nematic, smectic, and hexatic order parameters. Additionally, we investigate the radial pair distribution function, polarization correlation function, and the histogram of angles between molecular axes. The last characteristic is utilized to quantify local splay. The findings reveal that splay-induced deformations drive unusual long-range orientational order at relatively high packing fractions (η>0.5), corresponding to crystalline phases. When η<0.5, only short-range order is affected, and in addition to the isotropic liquid, only the standard nematic and smectic-A liquid crystalline phases are stabilized. However, for η>0.5, apart from the ordinary nonpolar hexagonal crystal, three additional frustrated crystalline polar blue phases with long-range splay modulation are observed: antiferroelectric splay crystal (Cr_{S}P_{A}), antiferroelectric double-splay crystal (Cr_{DS}P_{A}), and ferroelectric double-splay crystal (Cr_{DS}P_{F}). Finally, we employ Onsager-Parsons-Lee local density functional theory to investigate whether any sterically induced (anti)ferroelectric nematic or smectic-A type of ordering is possible for our system, at least in a metastable regime.

Realization of an inherent time crystal in a dissipative many-body system

Time crystals are many-body states that spontaneously break translation symmetry in time the way that ordinary crystals do in space. While experimental observations have confirmed the existence of discrete or continuous time crystals, these realizations have relied on the utilization of periodic forces or effective modulation through cavity feedback. The original proposal for time crystals is that they would represent self-sustained motions without any external periodicity, but realizing such purely self-generated behavior has not yet been achieved. Here, we provide theoretical and experimental evidence that many-body interactions can give rise to an inherent time crystalline phase. Following a calculation that shows an ensemble of pumped four-level atoms can spontaneously break continuous time translation symmetry, we observe periodic motions in an erbium-doped solid. The inherent time crystal produced by our experiment is self-protected by many-body interactions and has a measured coherence time beyond that of individual erbium ions.

Thunderstruck! A quasicrystal made by lightning

A material with characteristics between crystal and glass has been accidentally created by an electrical discharge (likely a lightning strike) in the Sand Hills of Nebraska. The material is a quasicrystal with 12-fold symmetry, impossible for ordinary crystals. Transient high-pressure and high-temperature conditions seem to ease the formation of quasicrystals in nature.

Solid-Liquid Crystal Biphasic Ferroelectrics with Tunable Biferroelectricity.

Ferroelectricity has been separately found in numerous solid and liquid crystal materials since its first discovery in 1920. However, a single material with biferroelectricity existing in both solid and liquid crystal phases is very rare, and the regulation of biferroelectricity has never been studied. Here, solid-liquid crystal biphasic ferroelectrics, cholestanyl 4-X-benzoate (4X-CB, X = Cl, Br, and I), which exhibits biferroelectricity in both the solid and liquid crystal phases, is presented. It is noted that the ferroelectric liquid crystal phase of 4X-CB is a cholesteric one, distinct from the ordinary chiral smectic ferroelectric liquid crystal phase. Moreover, 4X-CB shows solid-solid and solid-liquid crystal phase transitions, of which the transition temperatures gradually increase from Cl to Br to I substitution. The spontaneous polarization (Ps ) of 4X-CB in both solid and liquid crystal phases can also be regulated by different halogen substitutions, where the 4Br-CB has the optimal Ps because of the larger molecular dipole moment. To the authors' knowledge, 4X-CB is the first ferroelectric with tunable biferroelectricity, which offers a feasible case for the performance optimization of solid-liquid crystal biphasic ferroelectrics.

Spatial Frequency Manipulation of a Quartz Crystal for Phase‐Matched Second‐Harmonic Vacuum Ultraviolet Generation

AbstractSecond harmonic generation (SHG) is the nonlinear response of electrons to high‐intensity light and has been successfully applied in basic scientific research and modern optoelectronics. However, constrained by stringent but essential phase‐matching conditions, efficient vacuum ultraviolet (VUV) SHG is still a challenge in solid‐state lasers. Here, this work employs a spatial frequency manipulation strategy to realize artificially structured phase‐matching conditions in ordinary quartz crystals for efficient frequency doubling in the VUV range. Phase‐matched VUV SHG at wavelengths of 177.3 and 167.8 nm is realized with unprecedented output power and conversion efficiency. The design strategy releases the phase‐matching condition for nonlinear optics and provides a way to study light–matter nonlinear interactions, and the present sources should be helpful for the development of VUV photonics, including high‐resolution angle‐resolved photoemission spectroscopy and Al+ optical clocks.

Studies on the nature and pressure evolution of phase transitions in 1-adamantylamine and 1-adamantanol

In this paper, several experimental techniques, i.e., differential scanning calorimetry, X-ray diffraction, Fourier transform infrared, Raman, and broadband dielectric spectroscopy were applied to study the nature of the phase transitions in 1-adamantylamine (1-NH2-ADM, C10H17N) and 1-adamantanol (1-OH-ADM, C10H16O). Calorimetric measurements showed one and three endothermic peaks in thermograms for the latter and the former substance, respectively. Indeed, results of spectroscopic investigations indicated that the observed thermal events in 1-NH2-ADM correspond to transitions between various plastic crystal (PC) phases (I, II, III, IV), while the endothermic process in 1-OH-ADM can be assigned to a phase transition between the PC and the ordinary crystal (OC). Especially interesting were the outcomes of dielectric studies carried out both at ambient and high-pressure conditions, during heating and cooling cycles. They showed: i) noticeable changes in the frequency dependencies of the imaginary (ε'') and real (ε') parts of the complex dielectric permittivity that occurred around temperatures of the characteristic endothermic events detected by the calorimetry, and ii) significant fluctuations of ε'' and ε' at pressures attributed to the respective phase transitions. Moreover, the pressure coefficients of the phase transition temperatures were estimated to be approximately equal to 0.2 K/MPa for both compounds. In turn, volume variation (ΔV) at the PC (II)-PC (III) and PC (III)-PC (IV) transition temperatures for 1-NH2-ADM was essentially different than ΔV for the PC-OC transition in 1-OH-ADM.

Hydrodynamics of plastic deformations in electronic crystals

We construct a new hydrodynamic framework describing plastic deformations in electronic crystals. The framework accounts for pinning, phase, and momentum relaxation effects due to translational disorder, diffusion due to the presence of interstitials and vacancies, and strain relaxation due to plasticity and dislocations. We obtain the hydrodynamic mode spectrum and correlation functions in various regimes in order to identify the signatures of plasticity in electronic crystal phases. In particular, we show that proliferation of dislocations de-pins the spatially resolved conductivity until the crystal melts, after which point a new phase of a pinned electronic liquid emerges. In addition, the mode spectrum exhibits a competition between pinning and plasticity effects, with the damping rate of some modes being controlled by pinning-induced phase relaxation and some by plasticity-induced strain relaxation. We find that the recently discovered damping-attenuation relation continues to hold for pinned-induced phase relaxation even in the presence of plasticity and dislocations. We also comment on various experimental setups that could probe the effects of plasticity. The framework developed here is applicable to a large class of physical systems including electronic Wigner crystals, multicomponent charge density waves, and ordinary crystals.

Transverse Hypercrystals Formed by Periodically Modulated Phonon Polaritons

Photonic crystals and metamaterials are two overarching paradigms for manipulating light. By combining these approaches, hypercrystals can be created, which are hyperbolic dispersion metamaterials that undergo periodic modulation and mix photonic-crystal-like aspects with hyperbolic dispersion physics. Despite several attempts, there has been limited experimental realization of hypercrystals due to technical and design constraints. In this work, hypercrystals with nanoscale lattice constants ranging from 25 to 160 nm were created. The Bloch modes of these crystals were then measured directly using scattering near-field microscopy. The dispersion of the Bloch modes was extracted from the frequency dependence of the Bloch modes, revealing a clear switch from positive to negative group velocity. Furthermore, spectral features specific to hypercrystals were observed in the form of sharp density of states peaks, which are a result of intermodal coupling and should not appear in ordinary polaritonic crystals with an equivalent geometry. These findings are in agreement with theoretical predictions that even simple lattices can exhibit a rich hypercrystal bandstructure. This work is of both fundamental and practical interest, providing insight into nanoscale light-matter interactions and the potential to manipulate the optical density of states.

P‐12.4: Low Voltage Switchable Bistable Twist Nematic Display

The most common electronic paper technology is E‐ink, which enables many novel applications such as e‐readers, watches and electronic shelf labels. However, due to the TFT backplane driving and complex production processes, the cost of this technology is high, which limits its popularity. Recently, a low‐cost π‐bistable twist nematic (π‐BTN) liquid crystal display with a high pretilt angle is proposed. It has the same structure and production method as an ordinary liquid crystal display. Passive driving enables the manufacture of high‐resolution bistable displays without the use of thin‐film transistors. Compared with the current bistable twist nematic display technology, the high pretilt angles structure helps to achieve a lowvoltage and fast‐respond bistable display. This wide viewing angle, high contrast and TFT‐free display is a promising candidate for flexible displays.

Steering of one-way large-area waveguide modes in topological heterostructures with gyromagnetic photonic crystals

We study the steering of one-way and large-area topological waveguide modes in heterostructures consisting of a domain of ordinary photonic crystals sandwiched between two domains of magnetic-optical photonic crystals. Taking advantage of the band and mode properties of the topological heterostructures, we first demonstrate the design of four basic steering units which can realize the functionalities of forward-guiding, T-splitting, upward turning and downward turning. We demonstrate in detailed characteristic with the high-efficiency and broad-bandwidth of these basic steering units designed. Moreover, by combining these basic steering units, we implement a series of multifunctional waveguide devices, such as one-way large-area waveguide splitters with multiple channels and different angles, a highly bended large-area waveguide with five 90° corners along the propagation path, and waveguide structures supporting waveguide-cavity interaction, delay, splitting as well as storage functionalities. Importantly, all these different functionaries could be realized in a single system platform by simply reconfiguring the underlying magnetic field distributions. Our work opens up a new venue towards designing multi-functional waveguide devices by exploiting the width degree of freedom of the large-area waveguide modes.

Stability Against the Odds: The Case of Chromonic Liquid Crystals

The ground state of chromonic liquid crystals, as revealed by a number of recent experiments, is quite different from that of ordinary nematic liquid crystals: it is twisted instead of uniform. The common explanation provided for this state within the classical elastic theory of Frank demands that one Ericksen’s inequality is violated. Since in general such a violation makes Frank’s elastic free-energy functional unbounded below, the question arises as to whether the twisted ground state can be locally stable. We answer this question in the affirmative. In reaching this conclusion, a central role is played by the specific boundary conditions imposed in the experiments on the boundary of rigid containers and by a general formula that we derive here for the second variation in Frank’s elastic free energy.

Acoustic topological one-way waveguides with tunable widths using spinning components

We propose the topological one-way waveguide for acoustic waves whose width can be flexibly adjusted. The waveguide is constructed by a heterostructure where an ordinary phononic crystal is sandwiched by two time-reversal-symmetry-broken (TRS-broken) phononic crystals with their cylinders spinning in an opposite manner. The waveguide mode is confined to the ordinary phononic crystal and exhibits the gap-less and asymmetric dispersion. Therefore, we can tune the width of the waveguide by adjusting the thickness of the ordinary phononic crystal, and the waveguide mode is one-way transport which is robust against various types of local disorders and arbitrary bends. Owing to these, this acoustic topological one-way waveguide can meet the requirements of more applications compared with conventional waveguides and conventional one-way waveguides based on chiral surface waves.