Observation Of Phase Transition Research Articles

Synchronization transitions in phase oscillator populations with partial adaptive coupling.

The adaptation underlying many realistic processes plays a pivotal role in shaping the collective dynamics of diverse systems. Here, we untangle the generic conditions for synchronization transitions in a system of coupled phase oscillators incorporating the adaptive scheme encoded by the feedback between the coupling and the order parameter via a power-law function with different weights. We mathematically argue that, in the subcritical and supercritical correlation scenarios, there exists no critical adaptive fraction for synchronization transitions converting from the first (second)-order to the second (first)-order. In contrast to the synchronization transitions previously deemed, the explosive and continuous phase transitions take place in the corresponding regions as long as the adaptive fraction is nonzero, respectively. Nevertheless, we uncover that, at the critical correlation, the routes toward synchronization depend crucially on the relative adaptive weights. In particular, we unveil that the emergence of a range of interrelated scaling behaviors of the order parameter near criticality, manifesting the subcritical and supercritical bifurcations, are responsible for various observed phase transitions. Our work, thus, provides profound insights for understanding the dynamical nature of phase transitions, and for better controlling and manipulating synchronization transitions in networked systems with adaptation.

Amorphous to amorphous phase transformation in boron-rich amorphous silicon borides: an ab initio study

ABSTRACT This study employs a constant-pressure ab initio approach to investigate the high-pressure behavior of five distinct boron-rich amorphous silicon borides. A unique amorphous-to-amorphous phase transition is exposed, providing insights into the structural resilience of these materials under extreme conditions. Our results reveal a gradual increase in the coordination number of both B and Si atoms under pressure, with subsequent densification upon pressure release. Yet the recovered amorphous phases closely resemble the uncompressed states, highlighting the reversibility of these phase changes. Significant structural modifications around Si atoms are observed, emphasizing their pivotal role in the observed phase transitions. Additionally, pressure-induced metallization is witnessed in these materials, indicating their distinctive electronic behavior under high pressure. This work significantly contributes to a deeper understanding of the high-pressure behavior of boron-rich amorphous silicon borides and opens avenues for exploring their potential applications in fields requiring exceptional structural stability and unique pressure-dependent properties.

Multi-pulse Ramsey interferometry of a double-well Bose–Einstein condensate in a cavity

Ramsey interferometry as one of the most important high-precision measurement methods has prospects for inferring various properties of ultracold atoms and molecules. We investigate the multi-pulse Ramsey interferometry of a double-well Bose–Einstein condensate (BEC) in an optical cavity. Compared with the standard two-pulse Ramsey scheme, our multi-pulse Ramsey proposal greatly relaxes the requirements for both intensity and width of the pulses, allowing the interferometry to be achieved using weak and narrow pulses. When the pumping pulses characterizing the coupling between the cavity field and the atomic BEC are applied to the zero background field, we demonstrate the atomic Ramsey fringes in the time domain for different pulse numbers and different pulse widths. We find that although the multi-pulse Ramsey fringes are no longer sensitive to cavity-pump detuning, they can still record the information of the interaction between coherent atoms. We obtain the fundamental frequency of the multi-pulse Ramsey fringes analytically and find that it is proportional to the number of pulses. Particularly, it is shown that the minimum of the fundamental frequency is exactly the critical point of the phase transition of the system. For a nonzero background field, the results indicate that a nondestructive observation of atomic Ramsey fringes by cavity transmission spectroscopy is feasible. Our findings provide insights for improving the accuracy of Ramsey interferometry and for using interferometry to observe phase transitions.

Structure and piezochromism of chrysene at high pressures

Fluorescence materials have attracted great attention in the last decades because of their modulable fluorescence properties and broad applications. Molecular packing is one of the most important factors that determines organic molecular piezochromic fluorescence behavior. Herein, we systematically investigated the fluorescence, vibrational, and structural properties of chrysene up to 20 GPa by using multiple experimental techniques and ab-initio calculations. We find the obvious color-changing with increasing pressure. Meanwhile, the phase transition at a pressure of about 6.6 GPa has been identified from both the frequency shifts and the changes in intensity of the Raman modes. However, the structure of chrysene at ambient pressure remains stable to at least P∼20.2 GPa from both experimental and theoretical x-ray diffraction results. Further structural analysis indicates that the angle between two molecular planes decreases with pressure, resulting in the packing alteration. The combined results from the experiments and computations demonstrated that the observed phase transition at 6.6 GPa is probably a result of the change of molecular packing. Furthermore, the intermolecular interactions have changed correspondingly due to the change of the molecular packing, which results in the color-changing of chrysene under pressure. These results provide further evidence that the intermolecular interactions play the important role in tuning the photo-physical properties, and this work will contribute to understanding the relationship between molecular packing and piezochromism in fluorescence materials.

Acoustic Shock Wave-Induced Amorphous to Crystalline Phase Transitions of Li2SO4─Raman Spectroscopic and Thermal Calorimetric Approach.

In this context, we have reexamined the acoustical shock wave-induced amorphous-glassy-crystalline-amorphous phase transitions in the Li2SO4 sample under 0, 1, 2, and 3 shocked conditions by implementing the detailed Raman spectroscopic approach. The recorded Raman spectroscopic data clearly reveal that the transition from the amorphous-glassy-crystalline state occurs because of a significant reduction of the translational disorder of lithium cations, particularly [Li (2)] ions wherein a slight reduction of the librational disorder of SO4 anions takes place, whereas the crystalline to amorphous transition occurs only at the third shocked condition because of the librational disorder of SO4 anions. The double degenerate υ2 and υ4 Raman modes provide a clear indication of the occurrence of the librational disorder of SO4 anions at the third shocked condition. Followed by the internal Raman modes, a detailed discussion is provided on the external Raman modes of the Li ions and SO4 ions with respect to the observed phase transitions, wherein it is found that the regions of lattice modes are significantly altered at each and every point of phase transition. Furthermore, the thermal and magnetic measurements have been performed for the above-mentioned state of Li2SO4 samples, whereby the obtained results of the magnetic loops and the thermal property resemble the observed structural transitions with respect to the number of shock pulses such that the inter-relationship of the structure-electrical-magnetic-thermal properties of Li2SO4 could be explored.

Experimental Demonstration of Controllable PT and Anti-PT Coupling in a Non-Hermitian Metamaterial.

Non-Hermiticity has recently emerged as a rapidly developing field due to its exotic characteristics related to open systems, where the dissipation plays a critical role. In the presence of balanced energy gain and loss with environment, the system exhibits parity-time (PT) symmetry, meanwhile as the conjugate counterpart, anti-PT symmetry can be achieved with dissipative coupling within the system. Here, we demonstrate the coherence of complex dissipative coupling can control the transition between PT and anti-PT symmetry in an electromagnetic metamaterial. Notably, the achievement of the anti-PT symmetric phase is independent of variations in dissipation. Furthermore, we observe phase transitions as the system crosses exceptional points in both anti-PT and PT symmetric metamaterial configurations, achieved by manipulating the frequency and dissipation of resonators. This work provides a promising metamaterial design for broader exploration of non-Hermitian physics and practical application with a controllable Hamiltonian.

Investigation on the phase transition, geometric and electronic properties of Bi-doped CsPbBr3 perovskites

Given the ongoing debate regarding the potential impact of Bi dopant on the phase transition of CsPbBr3, our study aims to provide a comprehensive understanding of this phenomenon. Through a multifaceted examination encompassing energetic states, geometric configurations, bonding interactions, and electronic structures, we find that the inclusion of Bi dopants alone does not directly induce the orthorhombic/tetragonal phase transition in CsPbBr3. However, we observe a obvious reduction in the energetic discrepancy between these two phases, indicating an indirect stimulation of the phase transition by Bi dopants. This accelerates the stimulations originating from external environment, which may be responsible for the experimentally observed phase transition. Moreover, our investigation confirms that Bi dopants selectively weakens the bonding interaction within the Pb/Bi octahedra of the CsPbBr3 lattice in an anisotropic manner. Specifically, we identify that the weakening of the out-of-plane Bi–Br bond strength arises from the diminished bonding interaction between the p orbital of Bi and the s orbital of Br. This phenomenon results in the elongation of the metal-halide octahedra, consequently relaxing lattice distortions and twists in undoped CsPbBr3 systems, particularly pronounced in orthorhombic phases. Consequently, both orthorhombic and tetragonal CsPbBr3 lattices tend to evolve towards similar geometric configurations. Our findings reveal the significant influence of Bi dopants on the phase dynamics of CsPbBr3, a factor often overlooked in previous investigations.

Fractional quantum anomalous Hall effect in multilayer graphene.

The fractional quantum anomalous Hall effect (FQAHE), the analogue of the fractional quantum Hall effect1 at zero magnetic field, is predicted to exist in topological flat bands under spontaneous time-reversal-symmetry breaking2-6. The demonstration of FQAHE could lead to non-Abelian anyons that form the basis of topological quantum computation7-9. So far, FQAHE has been observed only in twisted MoTe2 at a moiré filling factor v > 1/2 (refs. 10-13). Graphene-based moiré superlattices are believed to host FQAHE with the potential advantage of superior material quality and higher electron mobility. Here we report the observation of integer and fractional QAH effects in a rhombohedral pentalayer graphene-hBN moiré superlattice. At zero magnetic field, we observed plateaus of quantized Hall resistance [Formula: see text] at v = 1, 2/3, 3/5, 4/7, 4/9, 3/7 and 2/5 of the moiré superlattice, respectively, accompanied by clear dips in the longitudinal resistance Rxx. Rxy equals [Formula: see text] at v = 1/2 and varies linearly with v, similar to the composite Fermi liquid in the half-filled lowest Landau level at high magnetic fields14-16. By tuning the gate-displacement field D and v, we observed phase transitions from composite Fermi liquid and FQAH states to other correlated electron states. Our system provides an ideal platform for exploring charge fractionalization and (non-Abelian) anyonic braiding at zero magnetic field7-9,17-19, especially considering a lateral junction between FQAHE and superconducting regions in the same device20-22.

Crystal structure analysis of the adduct 1:1 hexamethylenetetramine and succinic acid (HMT−C4) as a function of the temperature

Co−crystals of hexamethylenetetramine [N4(CH2)6, (HMT)] and dicarboxylic acids of general formula HOOC(CH2)n−2COOH with 4 ≤ n ≤ 14 (Cn), called HMT−Cn, exhibits structural properties strongly dependent on the length of the dicarboxylic acid chain, showing a wide variety of thermotropic phase transition sequence. This study focuses on describing the structural features of the HMT−C4 (1:1) adduct, a co-crystal of HMT and succinic acid (C4), exhibiting a reversible first-order phase transition at 222(4)K, as evidenced by differential scanning calorimetry (DSC) experiments. In contrast to a prior investigations , which did not identify this phase transition, our comprehensive temperature-dependent analysis, incorporating single crystal X-ray diffraction and DSC experiments, reveals a reversible structural change in the HMT−C4 (1:1) adduct structure upon cooling and heating. The crystal structures of the different observed phases are discussed in detail, emphasizing the role of O−H···N intermolecular hydrogen bonds in maintaining the connectivity between HMT and C4 molecules. The observed phase transition involves doubling the unit cell volume and significant reorientation of the −COOH groups at the end of the C4 chain at around 222(4)K. Our findings underscore the importance of additional temperature-dependent experiments, such as DSC, in avoiding erroneous structure modeling due to symmetry changes during temperature variations. The preservation of the acidic character of the C4 dicarboxylic chain throughout the temperature range adds additional insights to the understanding of the structural behavior of all the HMT−Cn (1:1) adducts.

Limitations of entanglement entropy in detecting thermal phase transitions

We explore the efficacy of entanglement entropy as a tool for detecting thermal phase transitions in a family of gauge theories described holographically. The rich phase diagram of these theories encompasses first and second-order phase transitions, as well as a critical and a triple point. While entanglement measures demonstrate some success in probing transitions between plasma phases, they prove inadequate when applied to phase transitions leading to gapped phases. Nonetheless, entanglement measures excel in accurately determining the critical exponent associated with the observed phase transitions, providing valuable insight into the critical behavior of these systems.

LoopSage: An energy-based Monte Carlo approach for the loop extrusion modeling of chromatin

The connection between the patterns observed in 3C-type experiments and the modeling of polymers remains unresolved. This paper presents a simulation pipeline that generates thermodynamic ensembles of 3D structures for topologically associated domain (TAD) regions by loop extrusion model (LEM). The simulations consist of two main components: a stochastic simulation phase, employing a Monte Carlo approach to simulate the binding positions of cohesins, and a dynamical simulation phase, utilizing these cohesins' positions to create 3D structures. In this approach, the system's total energy is the combined result of the Monte Carlo energy and the molecular simulation energy, which are iteratively updated. The structural maintenance of chromosomes (SMC) protein complexes are represented as loop extruders, while the CCCTC-binding factor (CTCF) locations on DNA sequence are modeled as energy minima on the Monte Carlo energy landscape. Finally, the spatial distances between DNA segments from ChIA-PET experiments are compared with the computer simulations, and we observe significant Pearson correlations between predictions and the real data. LoopSage model offers a fresh perspective on chromatin loop dynamics, allowing us to observe phase transition between sparse and condensed states in chromatin.

Synthesis of Eu-doped K0.5Na0.5NbO3 ceramics and their luminescent and dielectric properties

K0.5Na0.5NbO3:xEu sol–gel powders and bulk samples were synthesized by means of a modified sol–gel method. Two types of samples were obtained via sintering at two temperatures. X-ray diffraction revealed the presence of the perovskite phase in materials obtained at both temperatures. Eu3+ emission and excitation studies were conducted to determine its luminescence response. For K0.5Na0.5NbO3:xEu sinters, the excitation spectra included narrow peaks in the VIS range due to the 5D0–7F1 and 5D0–7F2 relaxation processes. These transitions were indicative of the presence of Eu3+ at sites of low symmetry. Dielectric studies indicated that Eu2O3 affected the observed phase transitions. The influence of sintering temperature on structure and physicochemical properties was discussed.

High-pressure properties of thallium orthovanadate from density-functional theory calculations

Thallium vanadate is the missing piece to fully understand the behavior of orthovanadates under high-pressure conditions. Here we report a computational study of TlVO4 under high pressure. Its properties and stability have been studied using the density-functional theory. We have found that TlVO4 undergoes at 2.7 GPa a phase transition from the CrVO4-type structure (described by space group Cmcm) to a wolframite-type structure (described by space group P2/c). In contrast to the behavior of isomorphic vanadates, a subsequent amorphization takes place beyond 6 GPa being it driven by dynamic instabilities. In addition to the structural analysis, we present a systematic study of elastic, vibrational, and bonding properties, as well as a characterization of the electronic band structure and electronic density of states. The distinctive behavior of TlVO4 is attributed to the contribution to the bonding of Tl 6s states. The implications of the observed phase transition and amorphization will be discussed.

Anderson Localization in the Subwavelength Regime

In this paper, we use recent breakthroughs in the study of coupled subwavelength resonator systems to reveal new insight into the mechanisms responsible for the fundamental features of Anderson localization. The occurrence of strong localization in random media has proved difficult to understand, particularly in physically derived multi-dimensional models and systems with long-range interactions. We show here that the scattering of time-harmonic waves by high-contrast resonators with randomly chosen material parameters reproduces the characteristic features of Anderson localization. In particular, we show that the hybridization of subwavelength resonant modes is responsible for both the repulsion of energy levels as well as the widely observed phase transition, at which point eigenmode symmetries swap and very strong localization is possible. We derive results from first principles, using asymptotic expansions in terms of the material contrast parameter and obtain a characterization of the localized modes in terms of generalized capacitance matrices. This model captures the long-range interactions of the wave-scattering system and provides a concise framework to explain the exotic phenomena that are observed.

Phase equilibrium determination of the binary system globalide + pressured propane: Experiments and thermodynamic modeling

Globalide is a macrolactone used recently as a monomer in polymerization processes in several kinds of research due to its ability to produce biodegradable and biocompatible polyesters suitable for applications in biodegradable packaging and biomedical devices. Polymerization processes traditionally use organic solvents and metallic/chemical catalysts that may leave toxic residues in the final polymer. To obtain polymers free of organic solvents, the use of pressurized gases as green solvents has been investigated. In this context, knowing the phase behavior of these systems is essential to understand the proper conditions of the polymerization process, ensuring that the reaction occurs in single-phase conditions. This work reports phase equilibrium studies of Gl + propane systems at temperatures of 313.15, 323.15, 333.15, and 343.15 K, and propane mass fractions between 0.1 and 0.9001. All observed phase transitions occur in pressures lower than 2.5 MPa, indicating that propane is a solvent that requires less energy expenditure than systems with CO2, being an economic advantage in the polymerization process. Peng-Robinson equation of state with a constant binary interaction parameter adjusted adjustment to the experimental data well.

An experimental setup for investigating the blowdown of liquid CO2 down to -50°C

In many Carbon Capture and Storage (CCS) technologies, CO2 is transported in a dense phase between 1 and 10 MPa, depending on the temperature. Previous investigations demonstrated that major accidents may occur during transportation or transfer operations in case of vessel or pipe depressurization to the atmosphere. Amongst the scenarios potentially leading to this, tank blowdown is a major concern due to two factors: the risk of brittle rupturing caused by low temperatures and the possibility of dry ice formation in the piping. Current flow models cannot properly model this, and further experimental evidence and detailed data are required.To provide the required information, a specific experimental setup was developed and tested. The tank is a 2 m3 sphere, carefully insulated and connected to a 40 mm diameter, 3 m long release pipe terminated by a discharge orifice to control the depressurization rate. The pipe can be connected either on the side of the vessel to release the gaseous phase or at the bottom to release the liquid phase.Optic ports are provided on the vessel and on the pipe to observe phase transition and monitor the liquid level. The instrumentation is a set of pressure transducers and arrays of thermocouples inside the CO2 and in the shell of the vessel. The tank is continuously weighed during the blowdown and the data are treated so that the mass flowrate can be obtained.The performance of the system is discussed based on a gaseous phase blowdown starting from a half-filled vessel with liquid CO2 at -38 °C and 1 MPa. Detailed data are presented and discussed. All phases - liquid, gas, and solid - appeared during the release, and temperatures dropped to nearly -80 °C in the shell and lasted for hours.

Bianchi type-III bulk-viscous string models in scalar–tensor theory of gravitation

In this paper, we have investigated Bianchi type-III bulk-viscous string cosmological models in the frame-work of scalar–tensor theory of gravitation. To solve the field equations for the bulk-viscous fluid and perfect fluid under the following physically relevant conditions: (i) Expansion scalar ([Formula: see text]) in the model is directly proportional to the shear scalar ([Formula: see text]). (ii) [Formula: see text], where [Formula: see text] is a constant (iii) [Formula: see text], where [Formula: see text] and [Formula: see text] are real constants. The observed phase transition of the presented universe from the early decelerating phase to the present epoch is in good accordance with the astronomical measurements. A detailed discussion on energy conditions and stability of the all models is analyzed through graphical representation.

Dielectric properties of (FeCoCrMnZn)3O4 high-entropy oxide at high pressure

The emerging high-entropy oxides (HEOs) have been considered promising candidates in numerous applications due to their unique properties. Yet the dielectric properties of HEOs at high pressure remain to be disclosed. In this work, the dielectric properties of (FeCoCrMnZn)3O4 at high pressures up to ∼20 GPa were systematically investigated. Combined with in-situ Raman, XRD, and impedance measurements, it is revealed that high-pressure exhibits a significant impact on the dielectric properties, even without the observed phase transition. The electric resistance, which is dominantly contributed by grain resistance, decreases exponentially with the increase of pressure. On the other hand, the relative permittivity decreases linearly with increasing pressure. In addition, the dielectric relaxation behavior of (FeCoCrMnZn)3O4 at high pressure is revealed. Our results provide the experimental basis for the high-pressure effect on the dielectric properties of (FeCoCrMnZn)3O4 and potential guidance for the design strategy of HEOs under extreme conditions.

High pressure Raman study of Na4Ca(CO3)3 from the ambient pressure to 11 GPa

ABSTRACT Na-Ca double carbonates were found as the inclusions in ‘superdeep’ Juina diamonds and as the products of high pressure experiments and thus are regarded as the potential host of CO2 in the deep mantle. Recently, Na-rich carbonate (21.0% wt. of Na2O vs. 13.6% wt. of CaO) was reported as the product of experiment with carbonated eclogite treated at 21 GPa and 1200°C. Na/Ca ratio of this carbonate corresponds to Na4Ca(CO3)3 phase with cubic symmetry synthesized at 6 GPa. The stability of Na4Ca(CO3)3 at higher pressures has not been investigated yet. Herein, we report an in situ Raman study of Na4Ca(CO3)3 carbonate up to 11 GPa in order to reveal stability of its structure at mantle pressures. Obtained results strongly imply for reversible phase transition near 8 GPa associated with decrease of symmetry. The observed phase transition questions the stability of cubic Na4Ca(CO3)3 under conditions of mantle transition zone.

Probing quantum phase transition point by tuning an external anti trap.

Manipulation of ultracold atoms in optical lattices is one of the optimal ways to observe phase transitions of the Hubbard model which is useful in a variety of condensed-matter systems. Bosonic atoms in this model experience a phase transition from superfluids to Mott insulators by tuning systematic parameters. However, in conventional setups, phase transitions take place over a large range of parameters instead of one critical point due to the background inhomogeneity caused by the Gaussian shape of optical-lattice lasers. To probe the phase transition point more precisely in our lattice system, we apply a blue-detuned laser to compensate for this local Gaussian geometry. By inspecting the change of visibility, we find a sudden jump point at one particular trap depth of optical lattices, corresponding to the first appearance of Mott insulators in inhomogeneous systems. This provides a simple method to detect the phase transition point in such inhomogeneous systems. We believe it will be a useful tool for most cold atom experiments.