Liquid Regime Research Articles

Anomalously strong viscosity behavior in mixed oxy-sulfide Na4P2S7-xOx invert glasses

In this report, the first observations of the anomalously strong viscosity behavior in the melt quenched (MQ) invert mixed oxy-sulfide Na4P2S7-xOx, 0 ≤ x ≤ 5, (NaPSO) glass series. We find that these glasses even with 67 mole% modifier, Na2S, exhibit a calorimetric fragility index, mcal, as small as 29 compared to typical values of ~ 60 to 80 for alkali silicate glasses with > 50 mole% SiO2. We find that the calorimetric fragility of these glasses varies systematically with the extent of network forming bridging oxygens (BOs) in the glasses. The mcal values were converted to kinetic fragility (mvis) values and used with the measured Tgs to produce viscosity curves for the glasses using the Mauro-Yue-Ellison-Gupta-Allan (MYEGA) model. The viscosity of the glass with a minimum mcal value of x = 2.5 was then shown to exhibit a viscosity that was as strong as some alkali aluminosilicate glasses.In this report, the first observations have been made of anomalously strong viscosity behavior and correspondingly strong bulk glass formation and resistance to crystallization in a melt quenched (MQ) prepared series of invert, modifier content greater than the glass former content, mixed oxy-sulfide Na4P2S7-xOx, 0 ≤ x ≤ 5, (NaPSO) glasses. We find that these glasses even with 67 mole % modifier, Na2S, and only 33 mole% glass former P2S5-xOx, exhibit a calorimetric fragility index, mcal, as small as 29 compared to typical values of ~ 60 to 80 for alkali silicate glasses with > 50 mole% SiO2 and the theoretical minimum mcal of ~ 15. The mcal values were converted to kinetic viscosity fragility, mvis, values and used with the measured glass transition temperatures, Tgs, to produce viscosity curves for the glasses using the Mauro-Yue-Ellison-Gupta-Allan (MYEGA) model. The viscosity of the glass with a minimum mcal value of x = 2.5 was then shown to exhibit a viscosity that was as strong as, and for some compositions stronger than, the viscosity of alkali aluminosilicate glasses which have three dimensional network structures compared to the one dimensional chain structures observed in these MOS invert glasses. Consistent with these small values of fragility indices and therefore predicted higher viscosity above the glass transition temperature, Tg, in the supercooled liquid regime, these glasses are also particularly resistant to crystallization. For example, the x = 2.5 glass composition exhibits a crystallization temperature, TC, more than 150K above its Tg. We find that the calorimetric fragility of these glasses varies systematically with the extent of network forming bridging oxygens (BOs) in the glasses. The structural change caused by incrementally replacing sulfur with oxygen has been found to have consistent, large effects on the thermal properties.

Supercritical CO2 permeation in glassy polyimide membranes

The high-pressure permeation and sorption behavior of supercritical carbon dioxide (sc-CO2) in glassy Matrimid® 5218 polymer membranes were extensively investigated. The effect of pressure (0–120 bar) and temperature (25–55 °C) was examined. The observations were related to the intrinsic membrane properties, plasticization phenomena and the CO2 fluid properties. The phase transition from gaseous (-like sc) CO2 to liquid (-like sc) CO2 has the largest influence on the CO2 fluid properties and therefore was found to have the most influence on the CO2 sorption and CO2 permeability. The CO2 sorption was directly dependent on the CO2 density in the liquid (-like sc) regime. The CO2 permeability of Matrimid® 5218 showed typical CO2-induced plasticization behavior in the gaseous (-like sc) CO2 regime. When entering the liquid (-like sc) CO2 regime, the extent of plasticization was found to be independent of the applied feed pressure in this regime. The membranes showed strong hysteresis with pressure. The permeation history of the membrane thus has a large influence on the time-dependent permeability behavior. Clearly, the CO2 permeability behavior at these high pressures in glassy Matrimid® 5218 is determined by a combination of the CO2 fluid density and plasticization phenomena.

Precise Tuning of Band Structures and Electron Correlations by van der Waals Stacking of One-dimensional W6Te6 Wires.

Stacking of two-dimensional (2D) van der Waals (vdW) atomic sheets has been established as a powerful approach to fabricating new materials with broad versatilities and emergent functionalities. Here we demonstrate a bottom-up approach to fabricating isolated single W6Te6 wires and their lateral assemblies, offering a unique platform for investigating the elegant role of vdW coupling in 1D systems with atomic precision. We find experimentally and theoretically a single W6Te6 wire is a 1D semiconductor with a band gap of ∼60 meV, and a semiconductor-to-metal transition takes place upon interwire vdW stacking. The metallic multiwires exhibit strong Tomonaga-Luttinger liquid characteristics with the correlation parameter g varying from g = 0.086 for biwire to g = 0.136 for six-wire assemblies, all much reduced from the Fermi liquid regime (g = 1). The present study demonstrates wire-by-wire vdW stacking is a versatile means for fabrication of 1D systems with tunable electronic properties.

Shock compression of vanadium at extremes: Theory and experiment

The equation of state (EOS) and shock compression of bulk vanadium were investigated using canonical ab initio molecular dynamic simulations, with experimental validation to 865 GPa from shock data collected at Sandia's Z Pulsed Power Facility. In simulations the phase space was sampled along isotherms ranging from 3000 K to $50\phantom{\rule{0.16em}{0ex}}000$ K, for densities between $\ensuremath{\rho}=3$ and $15\phantom{\rule{0.16em}{0ex}}\mathrm{g}/{\mathrm{cm}}^{3}$, with a focus on the liquid regime and the body-centered-cubic phase in the vicinity of the melting limit. The principal Hugoniot predicted from first principles is overall consistent with shock data, while it showed that current multiphase SESAME-type EOS for vanadium needed revision in the liquid regime. A more accurate SESAME EOS was developed using constraints from experiments and simulations. This work emphasizes the need to use a combined theoretical and experimental approach to develop high-fidelity EOS models for extreme conditions.

Interplay between spin-orbit coupling and Van Hove singularity in the Hund's metallicity of Sr2RuO4

We investigate the dynamical properties of Sr$_2$RuO$_4$ at zero and very low temperature using density functional theory plus dynamical mean-field theory with an exact diagonalization solver. By considering rotationally invariant local interaction, we examine how Hund's coupling and spin-orbit coupling affect the correlated nature of the system. In the absence of Hund's coupling, the system shows a Fermi liquid behavior over the entire range of temperatures we consider. We confirm that the Fermi liquid persists at zero temperature even with nonzero Hund's coupling; however, at sufficient temperatures Hund's coupling significantly reduces the Fermi liquid regime and the system evolves into a typical Hund's metal. At the bare electronic occupancy of Sr$_2$RuO$_4$ ($t_{2g}^4$), a stronger Hund's metallicity accompanies a larger long-time correlator. Remarkably, electron doping further destabilizes the Fermi liquid even though the long-time correlator and magnetic fluctuations decrease upon doping. This suppression of the Fermi liquid is driven by the van Hove singularity above the Fermi level in Sr$_2$RuO$_4$, combined with an enhanced Van Vleck susceptibility by spin-orbit coupling. Such findings point to the important role that electronic structure plays in the behavior of Hund's metals, in addition to magnetic fluctuations.

Flux pinning mechanisms of (YBa2Cu3Oy-d)1−x/(Dy2O3)x superconductors (x=0.1 and 0.5 wt%)

Polycrystalline (YBa2Cu3Oy-d)1−x/(Dy2O3)x superconductor samples were produced through the solid-state reaction route and by adding amounts of x = 0.1 and 0.5 wt% of Dy2O3 nanoparticles (NP-Dy2O3 with a size of about 10 nm) during the second stage of heat treatment. The structural, microstructural, critical current density and pinning properties were investigated using x-ray diffraction, scanning electron microscope, and DC magnetization at various temperatures ranging from 77 down to 10 K and under an applied magnetic field varying between −6 and +6 Tesla. Both samples crystallize in the orthorhombic structure. It was found that the Dy2O3 nanoparticles reside in the grain boundaries. Although the sample with 0.5 wt% NP-Dy2O3 is characterized by a low zero resistive temperature of about 78 K that is close to the useful temperature for technological applications, it showed the highest Jc values and the excellent flux pinning capacity. The addition of an appropriate amount of NP-Dy2O3 up to 0.5 wt% extends the single bundle pinning regime and retards the liquid vortex regime.

Exciton Vortices in Two-Dimensional Hybrid Perovskite Monolayers* *Supported by the National Key R&D Programme of China (Grant Nos. 2017YFA0303400 and 2016YFE0110000), the National Natural Science Foundation of China (Grant Nos. 11574303 and 11504366), the Youth Innovation Promotion Association of Chinese Academy of Sciences (Grant No. 2018148), and the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDB28000000).

We study theoretically the exciton Bose–Einstein condensation and exciton vortices in a two-dimensional (2D) perovskite (PEA)2PbI4 monolayer. Combining the first-principles calculations and the Keldysh model, the exciton binding energy of in a (PEA)2PbI4 monolayer can approach hundreds of meV, which make it possible to observe the excitonic effect at room temperature. Due to the large exciton binding energy, and hence the high density of excitons, we find that the critical temperature of the exciton condensation could approach the liquid nitrogen regime. In the presence of perpendicular electric fields, the dipole-dipole interaction between excitons is found to drive the condensed excitons confined in (PEA)2PbI4 monolayer flakes into patterned vortices, as the evolution time of vortex patterns is comparable to the exciton lifetime.

Experimental tests for a liquid-liquid critical point in water

Water is a fascinating material. Its composition is simple—one oxygen andtwo hydrogen atoms—but its chemistry and physics are extremely complex andexhibit 75 documented anomalies. Although these anomalies and theirmolecular origin are not completely understood, we know that hydrogen bondsplay key roles in all of the phases of water. Moreover, there isexperimental evidence that the polymorphism of the ice structure extendsinto the liquid phase and is associated with a liquid-liquid coexistenceline. This is currently a topic of great interest in water research becausethere are indications that the end point of the coexistence line correspondsto a second critical point inside the supercooled liquid regime. We examinethe recent progress in understanding water anomalies and the liquid-liquidphase transition hypothesis, including the results of recent experimentalwork and molecular simulations of both bulk and confined water. We examineexperimental results that test whether the behavior of liquid water isconsistent with the textquotedblleft liquid polymorphismtextquotedblrighthypothesis that liquid water can exist in two distinct phases of differingdensities. We also examine recent research on the anomalies of nanoconfinedwater and, in particular, on water in biological environments. We find thatthe concept of liquid polymorphism can also describe the properties of otherliquids that have two characteristic length scales.

Channel-selective non-Fermi liquid behavior in the two-channel Kondo lattice model under a magnetic field

Stimulated by anomalous behaviors found in non-Kramers $f$-electron systems in an applied magnetic field, we study a two-channel Kondo lattice model by using a cluster extension of the dynamical mean-field theory combined with the continuous-time quantum Monte Carlo method. We include the effect of the external magnetic field in two ways: the Zeeman coupling to conduction electron spins and an effective coupling to the quadrupole degree of freedom through the crystalline electric field splitting. We show that the magnetic field suppresses the antiferroic-spin order (physically, corresponding to the antiferroic-quadrupole order), and yields a channel-selective non-Fermi liquid state where one of the two channels (physically, spin-up or -down) exhibits non-Fermi liquid behavior while the other shows Fermi liquid behavior, before entering the Fermi liquid regime in higher fields. This anomalous state appears in a dome-shaped region which extends from inside the antiferroic-spin ordered phase to the paramagnetic phase. We find that the composite correlation, which is a measure of differentiation in the Kondo coupling between the two channels, is enhanced in this dome-shaped region. We also find that the specific heat coefficient is enhanced in this region in the paramagnetic side, indicating heavy fermion behavior not only in the vicinity of the critical field where the antiferroic-spin order vanishes but also in a certain region of the field and temperature. We discuss the results in comparison with the ordinary Kondo lattice model. We also discuss the implication of our findings to the peculiar behavior observed in the 1-2-20 compounds such as $\rm{PrIr_2Zn_{20}}$, $\rm{PrRh_2Zn_{20}}$, and $\rm{PrV_2Al_{20}}$ under a magnetic field.

Composition fluctuations in polydisperse liquids: Glasslike effects well above the glass transition.

We study a two-dimensional glass-forming system of slightly polydisperse (LJ) particles using molecular dynamics simulations and demonstrate that in the liquid regime (well above the vitrification temperature) this model shows a number of features typical of the glass transition: (i) the relation between compressibility and structure factor S(q) is strongly violated; (ii) the dynamical structure factor S(q,t) at low q shows a two-step relaxation; (iii) the time-dependent heat capacity c_{v}(t) shows a long-time power-law tail. We show that these phenomena can be rationalized with the idea of composition fluctuations and provide a quantitative theory for the effects (i) and (ii). It implies that such effects must be inherent in all polydisperse colloidal models, including binary LJ mixtures.

Fingerprints of Kitaev physics in the magnetic excitations of honeycomb iridates

In the quest for realizations of quantum spin liquids, the exploration of Kitaev materials - spin-orbit entangled Mott insulators with strong bond-directional exchanges - has taken center stage. However, in these materials the local spin-orbital j=1/2 moments typically show long-range magnetic order at low temperature, thus defying the formation of a spin-liquid ground state. Using resonant inelastic x-ray scattering (RIXS), we here report on a proximate spin liquid regime with clear fingerprints of Kitaev physics in the magnetic excitations of the honeycomb iridates alpha-Li2IrO3 and Na2IrO3. We observe a broad continuum of magnetic excitations that persists up to at least 300K, more than an order of magnitude larger than the magnetic ordering temperatures. We prove the magnetic character of this continuum by an analysis of the resonance behavior. RIXS measurements of the dynamical structure factor for energies within the continuum show that dynamical spin-spin correlations are restricted to nearest neighbors. Notably, these spectroscopic observations are also present in the magnetically ordered state for excitation energies above the conventional magnon excitations. Phenomenologically, our data agree with inelastic neutron scattering results on the related honeycomb compound RuCl3, establishing a common ground for a proximate Kitaev spin-liquid regime in these materials.

Strongly coupled Yukawa trilayer liquid: Structure and dynamics.

The equilibrium structure and the dispersion relations of collective excitations in trilayer Yukawa systems in the strongly coupled liquid regime are examined. The equilibrium correlations reveal a variety of structures in the liquid phase, reminiscent of the corresponding structures in the solid phase. At small layer separation substitutional disorder becomes the governing feature. Theoretical dispersion relations are obtained by applying the quasilocalized charge approximation (QLCA) formalism, while numerical data are generated by microcanonical molecular dynamics simulations. The dispersions and polarizations of the collective excitations obtained through both of these methods are compared and discussed in detail. We find that the QLCA method is, in general, very satisfactory, but that there are phenomena not covered by the QLCA. In particular, by analyzing the dynamical longitudinal and transverse current fluctuation spectra we discover the existence of a structure not related to the collective mode spectra. This also provides insight into the long-standing problem of the gap frequency discrepancy, observed in strongly coupled layered systems in earlier studies.

Deformation and regimes of liquid column during water exit of a partially submerged sphere using the front-tracking lattice Boltzmann method

When a solid sphere exits water at a given velocity, the liquid column is pulled out of a liquid reservoir. The present study focuses on the dynamic deformation of the liquid column and on the identification of the liquid column regime on the Weber number and dimensionless time (We-t*) map. The three-dimensional model of water exit has been established on the basis of the lattice Boltzmann method. A mass tracking algorithm was incorporated to capture the free surface, where the liquid–gas​ two-phase flow is simplified to a single-phase free surface flow. The surface tension is included by adding a perturbation term and the gravity as a body force is introduced in form of calculating the equilibrium distribution with an altered velocity. The contact angle condition in numerical simulation is not considered. The accuracy of the numerical results is demonstrated through the comparisons with the prior numerical and the experimental results in the literature. A parametric study has been conducted numerically on the radius and volume and of liquid column. Besides, the relationship between the pinch-off time of a liquid column and the Froude number has been obtained. Moreover, the evolution of the liquid column shape with a wide range of the Weber number and time scales are discussed based on the number of ligaments and droplets. The liquid column exhibits different characteristics and has been divided into three regimes. The transition between different regimes has been analyzed and the critical Weber number is given.

Recipe for ultrafast and persistent phase-change memory materials

The contradictory nature of increasing the crystallization speed while extending the amorphous stability for phase-change materials (PCMs) has long been the bottleneck in pursuing ultrafast yet persistent phase-change random-access memory. Scandium antimony telluride alloy (ScxSb2Te3) represents a feasible route to resolve this issue, as it allows a subnanosecond SET speed but years of reliable retention of the RESET state. To achieve the best device performances, the optimal composition and its underlying working mechanism need to be unraveled. Here, by tuning the doping dose of Sc, we demonstrate that Sc0.3Sb2Te3 has the fastest crystallization speed and fairly improved data nonvolatility. The simultaneous improvement in such ‘conflicting’ features stems from reconciling two dynamics factors. First, promoting heterogeneous nucleation at elevated temperatures requires a higher Sc dose to stabilize more precursors, which also helps suppress atomic diffusion near ambient temperatures to ensure a rather stable amorphous phase. Second, however, enlarging the kinetic contrast through a fragile-to-strong crossover in the supercooled liquid regime should require a moderate Sc content; otherwise, the atomic mobility for crystal growth at elevated temperatures will be considerably suppressed. Our work thus reveals the recipe by tailoring the crystallization kinetics to design superior PCMs for the development of high-performance phase-change working memory technology.

Spin crossovers and superdiffusion in the one-dimensional Hubbard model

We use tools from integrability and generalized hydrodynamics to study finite-temperature dynamics in the one-dimensional Hubbard model. First, we examine charge, spin, and energy transport away from half-filling and zero magnetization, focusing on the strong coupling regime where we identify a rich interplay of temperature and energy scales, with crossovers between distinct dynamical regimes. We identify an intermediate-temperature regime analogous to the spin-incoherent Luttinger liquid, where spin degrees of freedom are hot but charge degrees of freedom are at low temperature. We demonstrate that the spin Drude weight exhibits sharp features at the crossover between this regime and the low-temperature Luttinger liquid regime, that are absent in the charge and energy response, and rationalize this behavior in terms of the properties of Bethe ansatz quasiparticles. We then turn to the dynamics along special lines in the phase diagram corresponding to half-filling and/or zero magnetization where on general grounds we anticipate that the transport is sub-ballistic but superdiffusive. We provide analytical and numerical evidence for Kardar-Parisi-Zhang (KPZ) dynamical scaling (with length and time scales related via $x\sim t^{2/3}$) along both lines and at the $SO(4)$-symmetric point where they intersect. Our results suggest that both spin-coherence crossovers and KPZ scaling may be accessed in near-term experiments with optical lattice Hubbard emulators.

Should carbon removal be treated as waste management? Lessons from the cultural history of waste

Carbon dioxide is a waste product of combusting fossil fuels, and its accumulation in the atmosphere presents a planetary hazard. Carbon dioxide is also managed and used as a resource. Emerging technologies like direct air capture present the opportunity to reclaim and re-use wasted carbon, and actors in industry and policy are increasingly understanding carbon capture, utilization and storage as a waste management process. What is the value, and the danger, of conceptualizing CO2 as a waste to be managed? This paper looks at the historical evolution of solid and liquid waste regimes to draw lessons for the future evolution of a gaseous waste regime. It finds that social decisions to clean up solid and liquid waste were driven by both culture and industry. Views of recycling and sanitation did not evolve smoothly, with recycling falling in and out of favour, and sanitation experiencing conflict between public and private actors. An earlier attempt to revalue waste as part of a circular economy—the 1930s scientific and industrial field of chemurgy—failed to become a durable term and movement. These experiences hold important takeaways for negative emissions technologies and carbon removal policy: technocratic ideas about resource management may not take hold without a broader popular movement, as in the case of chemurgy, but value change and technology development can support each other, as in the case of wastewater infrastructure. Scientists and carbon removal policy advocates have an opportunity to contextualize CO2 waste management within the struggles and goals of the larger circular economy project, and to focus simultaneously on both waste production and waste disposal.

Experimental and molecular dynamics simulation study on thermal, transport, and rheological properties of asphalt

The purpose of this study was to evaluate the thermal (glass transition temperature), transport (self-diffusion), and rheological (viscosity, storage and loss modulus) properties of asphalt via laboratory experiments and molecular dynamics simulations. A 12-component asphalt model was employed in the molecular dynamics simulations with the modified Amber-Cornell force field. The asphalt model with the specific force field was validated against experimental and literature density data at various temperatures. The transition from the glassy state to the viscoelastic regime was explored by calculating the glass transition temperature. The results were compared with results from the differential scanning calorimeter (DSC) experiments. The self-diffusivity was calculated at a broad temperature range. The viscosity at the viscoelastic liquid regime was measured in the laboratory and calculated with reverse non-equilibrium molecular dynamic (rNEMD) simulations at various temperatures. Laboratory dynamic shear rheological testing was conducted for a wide frequency range at 70 °C. Oscillatory shear was applied in the asphalt model for calculating the storage and loss moduli within the experimental frequency range.

Two-phase sparse-Lagrangian MMC-LES of dilute ethanol spray flames

A sparse Lagrangian particle method (MMC) is coupled with large eddy simulations (LES) and applied to a series of ethanol spray flames that cover a wide range of jet Reynolds numbers and droplet loadings. Varying degrees of pre-evaporation of the liquid favour mixed combustion regimes and pose severe challenges to any combustion model. Three flames with gas-phase equivalence ratios of 1.75, 0.53 and 0.05 (with overall equivalence ratios of the fuel jet of 4.5, 1.4 and 1.8) are investigated and the simulations are overall in good agreement with the measurements. The dependencies of droplet velocities, evaporation rates and mean droplet diameters on flow and flame conditions are captured well, with a possible exception of a persistent underprediction of the average diameter at far downstream locations. This could be improved by modified inflow conditions where droplets are injected through a nozzle pipe far upstream of the nozzle exit plane. This ensures a correlation between the carrier phase and droplet velocities at the burner injection plane. The predictions of temperature are good to reasonable with some qualitative differences within the central jet for flames with high droplet loadings. Further analysis of the MMC model demonstrates that particle mixing preserves localness in composition space throughout the domain despite the presence of pre-evaporation and the related deviations from a pure non-premixed flame regime. MMC-LES predictions are very good for fully turbulent spray flames where evaporation is relatively fast and mixing is dominated by turbulence.

Anisotropy-Induced Soliton Excitation in Magnetized Strong-Rung Spin Ladders.

We report low temperature electron spin resonance experimental and theoretical studies of an archetype S=1/2 strong-rung spin ladder material (C_{5}H_{12}N)_{2}CuBr_{4}. Unexpected dynamics is detected deep in the Tomonaga-Luttinger spin liquid regime. Close to the point where the system is half-magnetized (and believed to be equivalent to a gapless easy plane chain in zero field) we observed orientation-dependent spin gap and anomalous g-factor values. Field theoretical analysis demonstrates that the observed low-energy excitation modes in magnetized (C_{5}H_{12}N)_{2}CuBr_{4} are solitonic excitations caused by Dzyaloshinskii-Moriya interaction presence.

Thermoelectric Transport in a Three-Channel Charge Kondo Circuit.

We theoretically investigate the thermoelectric transport through a circuit implementation of the three-channel charge Kondo model quantum simulator [Z. Iftikhar etal., Science 360, 1315 (2018)SCIEAS0036-807510.1126/science.aan5592]. The universal temperature scaling law of the Seebeck coefficient is computed perturbatively approaching the non-Fermi liquid strong coupling fixed point using the Abelian bosonization technique. The predicted T^{1/3}logT scaling behavior of the thermoelectric power sheds light on the properties of Z_{3} emerging parafermions and gives access to exploring prefractionalized zero modes in the quantum transport experiments. We discuss a generalization of approach for investigating a multichannel Kondo problem with emergent Z_{N}→Z_{M} crossovers between "weak" non-Fermi liquid regimes corresponding to different low-temperature fixed points.