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Results for “Order fractionalization”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Possible continuous transition from fractional quantum Hall to stripe phase at ν e = 7 / 3

We study the phase diagram of the ν e = 7/3 state in the N=1 Landau level in the presence of band mass anisotropy. Using the density matrix renormalization group on an infinite cylinder geometry, we find a continuous transition from the topologically ordered Laughlin fractional quantum Hall state to a stripe phase with a period of approximately five and a half magnetic lengths. The transition is driven by the condensation of the magnetoroton mode which becomes gapless at the critical point. We interpret the transition within the composite-boson theory as the onset of stripe order in a superfluid background, resulting from the roton mode going soft.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Spin waves above and below the Verwey transition in TbBaFe 2 O 5

TbBaFe 2 O 5+δ (TBFO) is a mixed valence compound with an antiferromagnetic order (T N =450K) that changes along with the crystal structure and conductivity upon cooling below a Verwey-like transition (TV=280K). This type of double-cell-layered perovskite is useful to study putative charge ordering in fractional valence systems because the crystal structure develops unique sites for the different valence states. While the evolution of the static magnetic structure in the different charge ordered states of TBFO is known, in this study we investigate the effect of charge ordering on the magnetic interactions. Dispersive magnetic excitations measured using single crystal inelastic neutron scattering experiments at T=4K V and T=320K>T V are modeled with linear-spin-wave theory to extract anisotropy and superexchange parameters. Below T V , we observe a sizable magnon gap due to an easy-axis magnetic anisotropy that closes above T V due to the evolution of easy-plane anisotropy. The magnetic interactions are found to be highly three-dimensional and change across T V . Above T V , where the conductivity is greater, a damping term is required to model the spin waves that suggests a coupling to valence fluctuations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Spillway preheating

In traditional models only an order one fraction of energy is transferred from the inflaton to radiation through nonperturbative resonance production in preheating immediately after inflation, due to backreaction effects. We propose a particle production mechanism that could improve the depletion of the inflaton energy density by up to four orders of magnitude. The improvement comes from the fast perturbative decays of resonantly produced daughter particles. They act as a “spillway” to drain these daughter particles, reducing their backreaction on the inflaton and keeping the resonant production effective for a longer period. Thus we dub the scenario “spillway preheating”. We also show that the fraction of energy density remaining in the inflaton has a simple inverse power-law scaling in the scenario. In general, spillway preheating is a much more efficient energy dissipation mechanism, which may have other applications in model building for particle physics.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Understanding magnetic phase coexistence in Ru 2 Mn 1-x Fe x Sn Heusler alloys: A neutron scattering, thermodynamic, and phenomenological analysis

The random substitutional solid solution between the antiferromagnetic (AFM) full-Heusler alloy Ru 2 MnSn and the ferromagnetic (FM) full-Heusler alloy Ru 2 FeSn provides a rare opportunity to study FM-AFM phase competition in a near-lattice-matched, cubic system, with full solubility. At intermediate x in Ru 2 Mn 1-x Fe x Sn this system displays suppressed magnetic ordering temperatures, spatially coexisting FM and AFM order, and strong coercivity enhancement, despite rigorous chemical homogeneity. Here, we construct the most detailed temperature- and x-dependent understanding of the magnetic phase competition and coexistence in this system to date, combining wide-temperature-range neutron diffraction and small-angle neutron scattering with magnetometry and specific heat measurements on thoroughly characterized polycrystals. A complete magnetic phase diagram is generated, showing FM-AFM coexistence between x ≈ 0.30 and x ≈ 0.70. Furthermore, important insight is gained from the extracted length scales for magnetic phase coexistence (25–100 nm), the relative magnetic volume fractions and ordering temperatures, and remarkable x-dependent trends in magnetic and electronic contributions to specific heat. An unusual feature in the magnetic phase diagram (an intermediate FM phase) is also shown to arise from an extrinsic effect related to a minor Ru-rich secondary phase. The established magnetic phase diagram is then discussed with the aid of phenomenological modeling, clarifying the nature of the mesoscale phase coexistence with respect to the understanding of disordered Heisenberg models.

36 MATERIALS SCIENCE↗
DOE OSTI2025

A resonant valence bond spin liquid in the dilute limit of doped frustrated Mott insulators

Abstract Ideas about resonant valence bond liquids and spin–charge separation have led to key concepts in physics such as quantum spin liquids, emergent gauge symmetries, topological order and fractionalization. Despite extensive efforts to demonstrate the existence of a resonant valence bond phase in the Hubbard model that originally motivated the concept, a definitive realization has yet to be achieved. Here we present a solution to this long-standing problem by uncovering a resonant valence bond phase exhibiting spin–charge separation in realistic Hamiltonians. We show analytically that this ground state emerges in the dilute-doping limit of a half-filled Mott insulator on corner-sharing tetrahedral lattices with frustrated hopping, in the absence of exchange interactions. We confirm numerically that the results extend to finite exchange interactions, finite-sized systems and finite dopant density. Although much attention has been devoted to the emergence of unconventional states from geometrically frustrated interactions, our work demonstrates that kinetic energy frustration in doped Mott insulators may be essential for stabilizing robust, topologically ordered states in real materials.

Physics↗
DOE OSTI2024

Blowing in the dark matter wind

Abstract Interactions between dark matter and ordinary matter will transfer momentum, and therefore give rise to a force on ordinary matter due to the dark matter ‘wind.’ We show that this force can be maximal in a realistic model of dark matter, meaning that an order-1 fraction of the dark matter momentum incident on a target of ordinary matter is reflected. The model consists of light (m ϕ ≲ eV) scalar dark matter with an effective interaction$$ {\phi}^2\overline{\psi}\psi $$ ϕ 2 ψ ¯ ψ , whereψis an electron or nucleon field. If the coupling is repulsive and sufficiently strong, the fieldϕis excluded from ordinary matter, analogous to the Meissner effect for photons in a superconductor. We show that there is a large region of parameter space that is compatible with existing constraints, where the force is large enough to be detected by existing force probes, such as satellite tests of the equivalence principle and torsion balance experiments. However, shielding of the dark matter by ordinary matter prevents existing experiments from being sensitive to the dark matter force. We show that precise measurements of spacecraft trajectories proposed to test long distance modifications of gravity are sensitive to this force for a wide range of parameters.

Physics↗
DOE OSTI2021

Dilute Pd-in-Au alloy RCT-SiO 2 catalysts for enhanced oxidative methanol coupling

Dilute alloy catalysts have the potential to enhance selectivity and activity for large-scale reactions. Highly dilute Pd-in-Au nanoparticle alloys partially embedded in porous silica (“raspberry colloid templated” (RCT)-SiO 2 ) prove to be robust and selective catalysts for oxidative coupling of methanol. Palladium concentrations in the bimetallic nanoparticles as low as ~3.4 at.% catalyze the production of methyl formate with a selectivity of ~95% at conversions of ~55%, whereas conversions are low (<10%) for ~1.7 at.% Pd-in-Au nanoparticle and pure Au nanoparticle catalysts. Fractional reaction orders for both CH 3 OH and O 2 measured for ~3.4 at.% Pd-in-Au nanoparticles supported on RCT-SiO 2 indicated a complex mechanism in which the sites for O 2 dissociation are not saturated. Optimal methyl formate production was found for an equimolar mixture. There is no conversion of methanol in the absence of O 2 between 360 and 450 K. Finally, all observations are consistent with a mechanism derived from model studies, requiring that clusters of Pd be available on the catalyst for O 2 dissociation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

The small-angle neutron scattering extension in MCNPX and the SANS cross section for nanodiamonds

Detonation nanodiamonds provide an intriguing prospect for the development of a very cold neutron (VCN) source or as a high albedo material for VCN reflection helping to control leakage of cold and very cold neutrons in a moderator. The investigation of source and reflector designs necessitates the development of new simulation tools for existing Monte Carlo codes that include small angle neutron scattering (SANS). The SANS extension in MCNPX 2.7 provides an analytical model of hard-sphere scattering with variable scattering particle sizes, size distributions, and packing fractions in order to supplement currently existing scattering kernels as well as the capability to read an experimentally determined small angle neutron scattering profile from a data file. The SANS extension is discussed and compared to nanodiamond SANS measurements.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2022

Thermal Hydroquinone Oxidation on Co/N-doped Carbon Proceeds by a Band-Mediated Electrochemical Mechanism

Molecules catalyze aerobic oxidation reactions via redox cycling at the metal center to effect sequential activation of O 2 and the substrate. Metal surfaces can catalyze the same transformations by coupling independent half-reactions for oxygen reduction and substrate oxidation mediated via the exchange of band-electrons. Metal/nitrogen-doped carbons (MNCs) are promising catalysts for aerobic oxidation that consist of molecule-like active sites embedded in a conductive carbon host. Owing to their combining molecular and metallic features, it remains unclear whether they proceed via the sequential redox cycling pathways of molecules or the band-mediated pathways of metals. Herein, we simultaneously track the potential of the catalyst and the rate of the turnover of aerobic hydroquinone oxidation on a cobalt-based MNC catalyst contacted to a catalytically inactive carbon electrode. By comparing operando measurements of rate and potential with the current-voltage behavior of each constituent half-reaction under identical conditions, we show that these molecular materials can display the band-mediated reaction mechanisms of extended metallic solids. Further, we show that the action of these band-mediated mechanisms explains fractional reaction orders in both oxygen and hydroquinone, the time evolution of catalyst potential and rate, and the dependence of rate on overall reaction free energy. Selective poisoning experiments suggest that oxygen reduction proceeds at cobalt sites, whereas quinone oxidation proceeds at native oxidic defects on the carbon. These findings highlight that molecule-like active sites can take advantage of band-mediated mechanisms when coupled to conductive hosts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

The Frequency Shift and $Q$ of Disordered Superconducting RF Cavities

Niobium superconducting radio-frequency (SRF) cavities for high-energy accelerator applications have been greatly improved in terms of the quality factor $Q$ by techniques such as Nitrogen doping. However, the mechanisms leading to improvement in $Q$ are still not fully understood. Quite recently the SRF group at Fermilab measured anomalies in the frequency shift of N-doped SRF Niobium cavities near the transition temperature. Here we report our theoretical analysis of these results based on the microscopic theory of superconductivity that incorporates anisotropy of the superconducting gap and inhomogeneous disorder in the screening region of the SRF cavities. We are able to account for frequency shift anomalies very close to $T_c$ on the order of fractions of 1 kHz. Our results for the frequency shift and Q are in good agreement with the experimental data reported for all four N-doped Nb SRF cavities by Bafia et al. We also compare our theory with an earlier report on a Nb sample measured at 60 GHz. In addition, we show that the quality factor calculated theoretically has a peak of upper convexity with the largest $Q$ at intermediate levels of disorder. For strong disorder, i.e. the dirty limit, pair breaking in the presence of disorder and screening currents limits the $Q$.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

CHIME/FRB Catalog 1 Results: Statistical Cross-correlations with Large-scale Structure

The CHIME/FRB Project has recently released its first catalog of fast radio bursts (FRBs), containing 492 unique sources. Here, we present results from angular cross-correlations of CHIME/FRB sources with galaxy catalogs. We find a statistically significant (p-value ~ 10 –4 , accounting for look-elsewhere factors) cross-correlation between CHIME FRBs and galaxies in the redshift range 0.3 ≲ z ≲ 0.5, in three photometric galaxy surveys: WISE × SCOS, DESI-BGS, and DESI-LRG. The level of cross-correlation is consistent with an order-one fraction of the CHIME FRBs being in the same dark matter halos as survey galaxies in this redshift range. We find statistical evidence for a population of FRBs with large host dispersion measure (~400 pc cm –3 ) and show that this can plausibly arise from gas in large halos (M ~ 10 14 M ⊙ ), for FRBs near the halo center (r ≲ 100 kpc). These results will improve in future CHIME/FRB catalogs, with more FRBs and better angular resolution.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Understanding, quantifying, and controlling the molecular ordering of semiconducting polymers: from novices to experts and amorphous to perfect crystals

Molecular packing and texture of semiconducting polymers are often critical to the performance of devices using these materials. Although frameworks exist to quantify the ordering, interpretations are often just qualitative, resulting in imprecise use of terminology. Here, we reemphasize the significance of quantifying molecular ordering in terms of degree of crystallinity (volume fractions that are ordered) and quality of ordering and their relation to the size scale of an ordered region. We are motivated in part by our own imprecise and inconsistent use of terminology in the past, as well as the need to have a primer or tutorial reference to teach new group members. We strive to develop and use consistent terminology with regards to crystallinity, semicrystallinity, paracrystallinity, and related characteristics. To account for vastly different quality of ordering along different directions, we classify paracrystals into 2D and 3D paracrystals and use paracrystallite to describe the spatial extent of molecular ordering in 1–10 nm. We show that a deeper understanding of molecular ordering can be achieved by combining grazing-incidence wide-angle X-ray scattering and differential scanning calorimetry, even though not all aspects of these measurements are consistent, and some classification appears to be method dependent. We classify a broad range of representative polymers under common processing conditions into five categories based on the quantitative analysis of the paracrystalline disorder parameter (g) and thermal transitions. A small database is presented for 13 representative conjugated and insulating polymers ranging from amorphous to semi-paracrystalline. Lastly, we outline the challenges to rationally design more perfect polymer crystals and propose a new molecular design approach that envisions conceptual molecular grafting that is akin to strained and unstrained hetero-epitaxy in classic (compound) semiconductors thin film growth.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Tailoring Disordered/Ordered Phases to Revisit the Degradation Mechanism of High‐Voltage LiNi 0.5 Mn 1.5 O 4 Spinel Cathode Materials

Abstract In the spinel oxide cathode family, LiNi 0.5 Mn 1.5 O 4 (LNMO) shows a high operating voltage (≈4.7 V vs Li/Li + ) and excellent Li‐ion mobility with stable 3D conducting channels. Ni/Mn cation disordered and ordered phases usually coexist in LNMO materials, and they have distinct structural and electrochemical properties, resulting in different battery performances for LNMO materials with different phase compositions. Identifying the correlation between phase compositions and electrochemical properties is of significance to the improvement of battery performance and understanding of degradation mechanisms. Herein, the disordered/ordered phase compositions in LNMO materials are tailored by post‐annealing strategies and their impacts on electrochemical performance and degradation mechanisms from the surface to the bulk are systematically investigated. The ordered phase increases rapidly as Mn 3+ is oxidized to Mn 4+ through a post‐annealing process. LNMO with an intermediate fraction of disordered and ordered phases gives rise to improved cycling stability. This article further reports that a high ordered phase fraction can preferentially protect Ni from dissolution during cycling. However, these results suggest that the transition metal dissolution and surface structural change of LNMO do not exhibit a direct correlation with cycling stability. These results indicate the capacity fading mainly correlates with the bulk structural distortion, leading to decreased Li‐ion kinetics.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Low fractional volume superconductivity in single crystals of Pr{sub 4}Ni{sub 3}O{sub 10} under pressure

Magnetotransport measurements of P⁢r4⁢N⁢i3⁢O10 single crystals performed under externally applied pressures up to 73 GPa in diamond anvil cells with either KBr or Nujol oil as pressure media yield signatures of superconductivity with a maximum onset temperature of approximately 31 K. True zero resistance was not observed, consistent with a nonpercolating superconducting volume fraction. Magnetization measurements provided corroborating evidence of superconductivity, with a pressure-dependent diamagnetic signal occurring below the onset temperature, and an estimate from the absolute value of the susceptibility suggests a superconducting volume fraction on the order of 10%. We observe sample to sample variations in the magnitude and pressure dependence of 𝑇𝑐 as well as a dependence on the configuration of electrical contacts on a given sample. Possible causes of this behavior may be significant inhomogeneities in the pressure and/or damage to the samples induced by the pressure media as well as inhomogeneities in the crystals themselves. The results imply that our as-grown P⁢r4⁢N⁢i3⁢O10 single crystals are not bulk superconductors but that there is a minority structure present within the crystals that is indeed superconductin

Chen, Xinglong↗
DOE OSTI2022

Dynamically preferred state with strong electronic fluctuations from electrochemical synthesis of sodium manganate

Electrochemical (de)intercalation is a delicate method to precisely control the alkaline ion composition in alkaline transition metal oxides. Because of complicated interactions, metal charge ordering patterns can form spontaneously at special fractional alkaline compositions and orderings. In this study, we show that this elegant electrochemical process can create dynamically preferred structures in an anharmonic energy landscape that conventional syntheses and computations can rarely visit. Specifically, electrochemically prepared Na 1/2 MnO 2 ordering exhibits abnormal structure distortions, charge orderings, and dynamical activities. Strong magnetic fluctuations and lattice dynamics are observed in an unusually wide temperature range in Na 1/2 MnO 2 , which distinguishes it from all other Na x MnO 2 at higher or lower Na compositions. The results emphasize the unique opportunity of using electrochemical processes to design and create novel quantum states with strongly coupled and mutually enhanced electronic and lattice fluctuations, likely through a special dynamic charge flux functional, as suggested by our computational investigations.

25 ENERGY STORAGE↗
DOE OSTI2026

Mechanisms of Metal Additive-Induced Ordering During SNIPS Membrane Formation

Isoporous membranes can be fabricated by combining self-assembly with nonsolvent induced phase separation (SNIPS) using an amphiphilic block copolymer like polystyrene-b-poly(4-vinylpyridine) (SV). Poly(4-vinylpyridine) (V) is known to complex with metal salts, which are hypothesized to stabilize solution ordering and preserve structure during casting. We explored how the molar ratio of metal additive to the poly(4-vinylpyridine) block affected the final membrane morphology via scanning electron microscopy (SEM). Dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), and in situ grazing-incidence SAXS were used to track changes in solution ordering and chain conformation as a function of the molar ratio of the additive to the V block. Additives induced aggregation, promoted the formation of more compact conformations in solution, and facilitated micelle ordering onto lattices at optimal ratios. Furthermore, these experimental results were supported by random phase approximation calculations, which helped explain how the thermodynamic order–disorder transition shifts with additive binding strength. Stronger additive–polymer interactions reduced the block copolymer volume fraction required for ordering in solution, allowing ordered domains to form at lower polymer concentrations.

Additives↗
DOE OSTI2021

Electronic structures, charge transfer, and charge order in twisted transition metal dichalcogenide bilayers

Moiré superlattices of transition metal dichalcogenide (TMD) bilayers have been shown to host correlated electronic states, which arise from the interplay of long wavelength moiré potential and long-range Coulomb interaction. Here, we theoretically investigate structural relaxation and single-particle electronic structure of twisted TMD homobilayer. From the large-scale density functional theory calculation and continuum model with layer degrees of freedom, we find that the out-of-plane gating field creates a tunable charge transfer gap at the Dirac point between the first and second moiré valence bands. We further study the charge orders at the fractional band fillings. In the flat band limit, we find from Monte Carlo simulations a series of charge-ordered insulating states at various fillings $n = \frac{1}{4}, \frac{1}{3}, \frac{1}{2}, \frac{2}{3}, 1$. Further, we predict that gating field induces a phase transition between different electron crystals at fixed filling $n = \frac{1}{2}$ or $\frac{2}{3}$. At half-filling $\textit{n} = 1$, the ground state is a Mott insulator with electronically driven ferroelectricity. This work demonstrates that TMD homobilayer provides a powerful platform for the investigation of tunable charge transfer insulator and charge orders.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Using Bayesian Methodology to Estimate Liquefied Natural Gas Leak Frequencies

This analysis provides estimates on the leak frequencies of nine components found in liquefied natural gas (LNG) facilities. Data was taken from a variety of sources, with 25 different data sets included in the analysis. A hierarchical Bayesian model was used that assumes that the log leak frequency follows a normal distribution and the logarithm of the mean of this normal distribution is a linear function of the logarithm of the fractional leak area. This type of model uses uninformed prior distributions that are updated with applicable data. Separate models are fit for each component listed. Five order-of-magnitude fractional leak areas are considered, based on the flow area of the component. Three types of supporting analyses were performed: sensitivity of the model to the data set used, sensitivity of the leak frequency estimates to differences in the model structure or prior distributions, and sufficiency of sample sized used for convergence. Recommended leak frequency distributions for all component types and leak sizes are given. These leak frequency predictions can be used for quantitative risk assessments in the future.

03 NATURAL GAS↗