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At least 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Polar Nanodomains in a Ferroelectric Superconductor

The mechanisms by which itinerant carriers compete with polar crystal distortions is a key unresolved issue for polar superconductors, which offer new routes to unconventional Cooper pairing. Strained, doped SrTiO 3 films undergo successive ferroelectric and superconducting transitions, making them ideal candidates to elucidate the nature of this competition. Here, we reveal these interactions using scanning transmission electron microscopy studies of the evolution of polar nanodomains as a function of doping. These nanodomains are a precursor to the ferroelectric phase and a measure of long-range Coulomb interactions. With increasing doping, the magnitude of the polar displacements, the nanodomain size, and the Curie temperature are systematically suppressed. In addition, we show that disorder caused by the dopant atoms themselves presents a second contribution to the destabilization of the ferroelectric state. Furthermore, the results provide evidence for two distinct mechanisms that suppress the polar transition with doping in a ferroelectric superconductor.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Final technical report for project titled Quantitative Characterization of Cell Aggregation/Adhesion as Predictor for Distribution and Transport of Microorganisms in Subsurface Environment

This project aims to explore and develop enabling methodology and techniques for nano-scale characterization of microbe cell surface contact mechanics, interactions and adhesion quantities that allow for identification and quantification of indicative properties related to microorganism migration and transport behavior in porous media and in subsurface environments. Microbe transport has wide impact and therefore is of great interest in various environmental applications such as in situ or enhanced subsurface bioremediation,filtration processes for water and wastewater treatments and protection of drinking water supplies. Although great progress has been made towards understanding the identities and activities of these microorganisms in the subsurface, to date, little is known of the mechanisms that govern the mobility and transport of microorganisms in DOE’s contaminated sites, making the outcomes of in situ natural attenuation or contaminant stability enhancement unpredictable. Conventionally, movement of microorganisms was believed to follows the rules governing solute (particle) transport. However, recent studies revealed that cell surface properties, especially those pertaining to cell attachment/adhesion and aggregation behavior, can cause the microbe behavior to deviate from non-viable particles and hence greatly influence the mobility and distribution of microorganisms in porous media.This complexity highlights the need to obtain detailed information of cell-cell and cell-surface interactions in order to improve and refine the conceptual and quantitative model development for fate and transport of microorganisms and contaminant in subsurface. Traditional cell surface characterization methods are not sufficient to fully predict the deposition rates and transport behaviors of microorganism observed. A breakthrough of methodology that would allow for quantitative and molecular-level description of intrinsic cell surface properties indicative for cell-surface interactions is essential for the field. To tackle this, we have developed a number of new Bio-nanomechanical techniques, including reflection interference contrast microscopy (RICM) and bio-AFM (Atomic Force Microscopy), for cell adhesion-detachment measurement of the long-range surface interactions, in combination with mathematical modeling, which would allow us to characterize the mechanical behavior from single cell to multi-cell aggregate, critical thresholds for large scale coaggregation and transportation of cells and aggregates in the presence of long range inter-surface forces etc. Although some technical and mathematical challenges remain, the preliminary results promise great breakthrough potential. In this study, we investigated the cellular surface characteristics of representative bio-remediating microorganisms relevant to DOE IFRC (Integrated Field-Scale Subsurface Research Challenges) sites and their transport behaviors in porous media, aiming to draw a groundbreaking correlation between the micro-scale genetic and biological origin-based cell surface properties, the consequent mechanical adhesion and aggregation behaviors, and the macro-scale microbial mobility and retention in porous media, which are unavailable in the literature. The long-term goal is to significantly improve the mechanistic and quantitative understanding of microbial mobility, sorption, and transport within reactive transport models as needed to manipulate subsurface contaminant fate and transport predictions.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2016

Thermally induced magnetic relaxation in square artificial spin ice

The properties of natural and artificial assemblies of interacting elements, ranging from Quarks to Galaxies, are at the heart of Physics. The collective response and dynamics of such assemblies are dictated by the intrinsic dynamical properties of the building blocks, the nature of their interactions and topological constraints. Here in this paper, we report on the relaxation dynamics of the magnetization of artificial assemblies of mesoscopic spins. In our model nano-magnetic system $-$ square artificial spin ice $-$ we are able to control the geometrical arrangement and interaction strength between the magnetically interacting building blocks by means of nano-lithography. Using time resolved magnetometry we show that the relaxation process can be described using the Kohlrausch law and that the extracted temperature dependent relaxation times of the assemblies follow the Vogel-Fulcher law. The results provide insight into the relaxation dynamics of mesoscopic nano-magnetic model systems, with adjustable energy and time scales, and demonstrates that these can serve as an ideal playground for the studies of collective dynamics and relaxations.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

A computational approach for the annotation of hydrogen-bonded base interactions in crystallographic structures of the ribozymes

A fundamental understanding of the atomic level interactions in ribonucleic acid (RNA) and how they contribute towards RNA architecture is an important knowledge platform to develop through the discovery of motifs from simple arrangements base pairs, to more complex arrangements such as triples and larger patterns involving non-standard interactions. The network of hydrogen bond interactions is important in connecting bases to form potential tertiary motifs. Therefore, there is an urgent need for the development of automated methods for annotating RNA 3D structures based on hydrogen bond interactions. COnnection tables Graphs for Nucleic ACids (COGNAC) is automated annotation system using graph theoretical approaches that has been developed for the identification of RNA 3D motifs. This program searches for patterns in the unbroken networks of hydrogen bonds for RNA structures and capable of annotating base pairs and higher-order base interactions, which ranges from triples to sextuples. COGNAC was able to discover 22 out of 32 quadruples occurrences of the Haloarcula marismortui large ribosomal subunit (PDB ID: 1FFK) and two out of three occurrences of quintuple interaction reported by the non-canonical interactions in RNA (NCIR) database. These and several other interactions of interest will be discussed in this paper. These examples demonstrate that the COGNAC program can serve as an automated annotation system that can be used to annotate conserved base-base interactions and could be added as additional information to established RNA secondary structure prediction methods.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2010

CAN WE PROBE THE LORENTZ FACTOR OF GAMMA-RAY BURSTS FROM GeV-TeV SPECTRA INTEGRATED OVER INTERNAL SHOCKS?

We revisit the high-energy spectral cutoff originating from the electron-positron pair creation in the prompt phase of gamma-ray bursts (GRBs) with numerical and analytical calculations. We show that the conventional exponential and/or broken power-law cutoff should be drastically modified to a shallower broken power law in practical observations that integrate emissions from different internal shocks. Since the steepening is tiny for observations, this 'smearing' effect can generally reduce the previous estimates of the Lorentz factor of the GRB outflows. We apply our formulation to GRB 080916C, recently detected by the Large Area Telescope detector on the Fermi satellite, and find that the minimum Lorentz factor can be {approx}600 (or even smaller values), which is below but consistent with the previous result of {approx}900. Observing the steepening energy (the so-called 'pair-break energy') is crucial to diagnosing the Lorentz factor and/or the emission site in future observations, especially current and future Cherenkov telescopes such as MAGIC, VERITAS, and CTA.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Proceedings of RIKEN BNL Research Center Workshop: Multi-Hadron and Nonlocal Matrix Elements in Lattice QCD (Volume 120)

Nonperturbative QCD calculations of hadronic matrix elements are needed to understand the structure of the matter in our universe and to search for physics beyond the Standard Model. Numerical lattice gauge theory is uniquely suited for this task and has reached a remarkable level of precision. However, the types of observables that are accessible in a straightforward way are limited because lattice calculations are performed with imaginary time. Traditionally, lattice QCD determinations of hadronic matrix elements have been restricted to situations with at most one stable hadron in the initial and final states, and with a single insertion of a local current. This situation has been changing recently thanks to theoretical breakthroughs and pioneering numerical studies of new observables. At this workshop, the latest developments concerning multi-hadron systems and nonlocal matrix elements in lattice QCD were discussed: • Liischer's quantization condition relates the energy spectrum of two interacting particles in a finite volume to the scattering phase shifts. At this workshop, generalizations of Liischer's quantization condition to three-particle systems, and to two-particle systems with long-range QED interactions were presented. • Advanced numerical lattice QCD studies of hadronic resonances using the Liischer method were shown, including coupled-channel scattering and near-threshold resonances. • The Lellouch-Liischer formula relates two-hadron matrix elements computed in a finite volume to the infinite-volume matrix elements. This workshop included presentations of the latest numerical lattice QCD calculations ofthe nonleptonic weak decay K ® tl tl, as well as new theoretical results extending the Lellouch-Liischer formula to general multichannel 1 ® 2 transition matrix elements. • Novel methods allowing the direct calculation of parton distribution functions in lattice QCD were discussed, and a one-loop calculation of the lattice-to-continuum matching required for these methods was presented. • Lattice QCD calculations of nonlocal matrix elements relevant for rare kaon decays and for the Kl-Ks mass difference were shown. The inclusion of QED corrections in weak decays was discussed. Results from a new method for computing the hadronic light-by-light contribution to the muon anomalous magnetic moment were shown. • • Calculations of the binding energies and magnetic moments of light nuclei directly from lattice QCD were presented. The theoretical foundations of a potential-based method for studying multihadron interactions on the lattice were discussed, and an application of this method to charmed tetraquarks was shown.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

Detection of class I methanol (CH{sub 3}OH) maser candidates in supernova remnants

We have used the Karl G. Jansky Very Large Array to search for 36 GHz and 44 GHz methanol (CH{sub 3}OH) lines in a sample of 21 Galactic supernova remnants (SNRs). Mainly the regions of the SNRs with 1720 MHz OH masers were observed. Despite the limited spatial extent covered in our search, methanol masers were detected in both G1.4–0.1 and W28. Additional masers were found in Sgr A East. More than 40 masers were found in G1.4–0.1, which we deduce are due to interactions between the SNR and at least two separate molecular clouds. The six masers in W28 are associated with the molecular cloud that is also associated with the OH maser excitation. We discuss the possibility that the methanol maser may be more numerous in SNRs than the OH maser, but harder to detect due to observational constraints.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

Three-Dimensional Complex-Shaped Photopolymerized Microparticles at Liquid Crystal Interfaces

Microparticles of arbitrary shapes immersed in the bulk of nematic fluids are known to produce dipolar or quadrupolar elastic distortions that can mediate long-range colloidal interactions. We use two-photon photopolymerization to obtain complex-shaped surface-bound microparticles that are then embedded into a nematic liquid crystal host with a uniform far-field director. By means of three-dimensional imaging with multi-photon excitation fluorescence polarizing microscopy, we demonstrate low-symmetry, long-range elastic distortions induced by the particles in the liquid crystal director field. These director distortions may provide a means for controlling elastic interactions in liquid crystals between custom-designed photopolymerized microparticles attached to confining solid substrates and nematic fluid-borne colloids, thus enabling elasticity-mediated templated self-assembly.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Relativistic pair beams from TeV blazars: A source of reprocessed GeV emission rather than intergalactic heating

The interaction of TeV photons from blazars with the extragalactic background light produces a relativistic beam of electron-positron pairs streaming through the intergalactic medium (IGM). The fate of the beam energy is uncertain. By means of two- and three-dimensional particle-in-cell simulations, we study the nonlinear evolution of dilute ultra-relativistic pair beams propagating through the IGM. We explore a wide range of beam Lorentz factors γ {sub b} >> 1 and beam-to-plasma density ratios α << 1, so that our results can be extrapolated to the extreme parameters of blazar-induced beams (γ {sub b} ∼ 10{sup 6} and α ∼ 10{sup –15}, for powerful blazars). For cold beams, we show that the oblique instability governs the early stages of evolution, but its exponential growth terminates—due to self-heating of the beam in the transverse direction—when only a negligible fraction ∼(α/γ {sub b}){sup 1/3} ∼ 10{sup –7} of the beam energy has been transferred to the IGM plasma. Further relaxation of the beam proceeds through quasi-longitudinal modes, until the momentum dispersion in the direction of propagation saturates at Δp {sub b,} {sub ∥}/γ{sub b} m{sub e}c ∼ 0.2. This corresponds to a fraction ∼10% of the beam energy—irrespective of γ {sub b} or α—being ultimately transferred to the IGM plasma (as compared to the heating efficiency of ∼50% predicted by one-dimensional models, which cannot properly account for the transverse broadening of the beam). For the warm beams generated by TeV blazars, the development of the longitudinal relaxation is suppressed, since the initial dispersion in beam momentum is already Δp {sub b0,} {sub ∥}/γ {sub b} m{sub e}c ≳ 1. Here, the fraction of beam energy ultimately deposited into the IGM is only ∼α γ {sub b} ∼ 10{sup –9}. It follows that most of the beam energy is still available to power the GeV emission produced by inverse Compton up-scattering of the cosmic microwave background by the beam pairs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

Valence and origin of metal-insulator transition in Mn doped SrRuO{sub 3} studied by electrical transport, X-ray photoelectron spectroscopy and LSDA+U calculation

We have studied the valence and electronic properties of Mn doped SrRuO{sub 3} using electrical transport measurement, X-ray photoelectron spectroscopy (XPS) and local (spin) density approximation plus Coulomb interaction strength calculation (LSDA+U). The resistivity data revealed that the system undergoes transition from metal to insulator at the critical Mn doping level, x{approx}0.2, which is accompanied by the structural transition from orthorhombic to tetragonal crystal symmetry. Besides, the significant reduction of the spectral weight at the coherent zone (0.8 eV) of the valence band is observed for x>0.2. The core XPS spectra suggest that both the transition elements exist in the mixed ionic pair, Ru{sup +4}/Ru{sup +5{r_reversible}}Mn{sup +3}/Mn{sup +4}. The detail analysis of the results suggests that the Coulomb correlation effect in conjugation with localization of the charge carriers predominate over the mixed ionic pair effect and responsible for the metal-insulator transition in the series. -- Graphical Abstract: XPS data and electrical transport data show that doping of Mn in metallic SrRuO{sub 3} induces mixed ionic pair Ru(IV)/Ru(V){r_reversible}Mn(III)/Mn(IV) and the system undergoes a transition from metal to insulator at the critical Mn doping level, x{approx}0.2. The origin for the metal-insulator transition has been discussed. Display Omitted Research highlights: {yields} We have investigated the electronic properties of SrRu{sub 1-x}Mn{sub x}O{sub 3} spectroscopically, which shows metal-insulator transition at the critical Mn doping concentartion x{approx}0.2. {yields} We report the valence states of Ru and Mn in the series. {yields} We also report the responsible mechanism for the metal-insulator transition in the series.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Oxygen vacancy induced by La and Fe into ZnO nanoparticles to modify ferromagnetic ordering

We reported long-range ferromagnetic interactions in La doped Zn{sub 0.95}Fe{sub 0.05}O nanoparticles that mediated through lattice defects or vacancies. Zn{sub 0.92}Fe{sub 0.05}La{sub 0.03}O (ZFLaO53) nanoparticles were synthesized by a sol–gel process. X-ray fluorescence spectrum of ZFLaO53 detects the weight percentage of Zn, Fe, La and O. X-ray diffraction shows the hexagonal Wurtzite ZnO phase. The Rietveld refinement has been used to calculate the lattice parameters and the position of Zn, Fe, La and O atoms in the Wurtzite unit cell. The average size of ZFLaO53 nanoparticles is 99 nm. The agglomeration type product due to OH ions with La results into ZnO nanoparticles than nanorods that found in pure ZnO and Zn{sub 0.95}Fe{sub 0.05}O sample. The effect of doping concentration to induce Wurtzite ZnO structure and lattice defects has been analyzed by Raman active vibrational modes. Photoluminescence spectra show an abnormal emission in both UV and visible region, and a blue shift at near band edge is formed with doping. The room temperature magnetic measurement result into weak ferromagnetism but pure ZnO is diamagnetic. However, the temperature dependent magnetic measurement using zero-field and field cooling at dc magnetizing field 500 Oe induces long-range ferromagnetic ordering. It results into antiferromagnetic Neel temperature of ZFLaO53 at around 42 K. The magnetic hysteresis is also measured at 200, 100, 50 and 10 K measurement that indicate enhancement in ferromagnetism at low temperature. Overall, the La doping into Zn{sub 0.95}Fe{sub 0.05}O results into enhanced antiferromagnetic interaction as well as lattice defects/vacancies. The role of the oxygen vacancy as the dominant defects in doped ZnO must form Bound magnetic polarons has been described. - Graphical abstract: The long-range ferromagnetic order in Zn{sub 0.92}Fe{sub 0.05}La{sub 0.03}O nanoparticles at low temperature measurements involves oxygen vacancy as the medium of magnetic interactions. - Highlights: • The La and Fe doping into ZnO nanoparticles induce defects in terms of oxygen vacancy. • The La ions in Fe substituted ZnO formed nanoparticles than nanorods. • Antiferromagnetic interactions are observed at room temperature magnetic measurement. • Rietveld analysis evaluated structural deformation in the Wurtzite ZnO lattice.

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

Influence of solutes on the core structures of $\langle$ α $\rangle$-type screw dislocations in $α$-Ti

The $\langle$ α $\rangle$-type screw dislocations are known to be significant mediators of plasticity in hexagonal-close-packed (HCP) metals. These dislocations have polymorphic core structures, and subtle changes in the relative energies of these core structures are known to have a large impact on the dynamics of the dislocations. Here, this work identifies a previously neglected long-range elastic interstitial-solute/dislocation interaction that influences the core structures. Essentially, interstitial solutes induce a change in the dislocation core structure to minimize the energy of interaction between the solutes and the dislocation. Molecular dynamics simulations, continuum linear elasticity, and statistical analysis show that this long-range interaction can locally alter the dislocation cores so that many different polymorphs appear along a single dislocation not only because of direct contact between interstitials and the dislocation core but also because of this long-range elastic interaction.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Precise Experimental Test of the Luttinger Theorem and Particle-Hole Symmetry for a Strongly Correlated Fermionic System

A fundamental concept in physics is the Fermi surface, the constant-energy surface in momentum space encompassing all the occupied quantum states at absolute zero temperature. In 1960, Luttinger postulated that the area enclosed by the Fermi surface should remain unaffected even when electron-electron interaction is turned on, so long as the interaction does not cause a phase transition. Understanding what determines the Fermi surface size is a crucial and yet unsolved problem in strongly interacting systems such as high-$T_c$ superconductors. Here we present a precise test of the Luttinger theorem for a two-dimensional Fermi liquid system where the exotic quasiparticles themselves emerge from the strong interaction, namely, for the Fermi sea of composite fermions (CFs). Via direct, geometric resonance measurements of the CFs’ Fermi wave vector down to very low electron densities, we show that the Luttinger theorem is obeyed over a significant range of interaction strengths, in the sense that the Fermi sea area is determined by the density of the minority carriers in the lowest Landau level. Our data in this work also address the ongoing debates on whether or not CFs obey particle-hole symmetry, and if they are Dirac particles. We find that particle-hole symmetry is obeyed, but the measured Fermi sea area differs quantitatively from that predicted by the Dirac model for CFs.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Constraints on the hadronic content of gamma ray bursts

The IceCube High-energy Neutrino Telescope has been collecting data since 2006. Conversely, hundreds of gamma-ray bursts (GRBs) have been detected by the GRB Monitor on board Fermi since its launch in 2008. So far no neutrino event has been associated with a GRB, despite many models predicting the generation of high-energy neutrinos through GRB photon interaction with PeV protons in the GRB jet. We use the non-detection of neutrinos to constrain the hadronic content of GRB jets independent of jet model parameters. Assuming a generic particle spectrum of E {sup –α} with α = 2, we find that the ratio of the energy carried by pions to that in electrons has to be small f {sub π}/f{sub e} ≲ 0.24 at 95% confidence level. A distribution of spectral slopes can lower f {sub π}/f{sub e} by orders of magnitude. Another limit, independent of neutrinos, is obtained if one ascribes the measured Fermi/Large Area Telescope GeV gamma-ray emission to pair-photon cascades of high-energy photons resulting from (the same photon-hadronic interactions and subsequent) neutral pion decays. Based on the generally observed MeV-to-GeV GRB fluence ratio of ≈10, we show that f {sub π}/f{sub e} ≲ 0.3. In some bursts, this ratio is as low as unity, f {sub π}/f{sub e} ≲ 0.03. These findings add to mounting doubts regarding the presence of PeV protons in GRB jets.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Measurement of New Observables from the pi+pi- Electroproduction off the Proton

Knowledge of the Universe as constructed by human beings, in order to tackle its complexity, can be thought to be organized at varying scales at which it is observed. Implicit in such an approach is the idea of a smooth evolution of knowledge between scales and, therefore, access to how Nature constructs the visible Universe beginning from its most fundamental constituents. New and, in a sense, fundamental phenomena may typically be emergent as the scale of observation changes. The study of the Strong Interaction, which is responsible for the construction of the bulk of the visible matter in the Universe (98% by mass), in this sense, is a labor of exploring evolutions and unifying aspects of its knowledge found at varying scales ranging from interaction of quarks and gluons as represented by the theory of Quantum Chromodynamics (QCD) at small space-time scale to emerging dressed quark and even meson-baryon degrees of freedom mostly described by effective models as the space-time scale increases. A direct effort to study the Strong Interaction over this scale forms the basis of an international collaborative effort often referred to as the N* program. The core work of this thesis is an experimental analysis prompted by the need to measure experimental observables that are of particular interest to the theory-experiment epistemological framework of this collaboration. While the core of this thesis, therefore, discusses the nature of the experimental analysis and presents its results which will serve as input to the N* program's epistemological framework, the particular nature of this framework in the context of not only the Strong Interaction, but also that of the physical science and human knowledge in general will be used to motivate and introduce the experimental analysis and its related observables.

Trivedi, Arjun↗
DOE OSTI2017

Understanding lattice defects to influence ferromagnetic order of ZnO nanoparticles by Ni, Cu, Ce ions

Future spintronics technologies based on diluted magnetic semiconductors (DMS) will rely heavily on a sound understanding of the microscopic origins of ferromagnetism in such materials. It remains unclear, however, whether the ferromagnetism in DMS is intrinsic - a precondition for spintronics - or due to dopant clustering. For this, we include a simultaneous doping from transition metal (Ni, Cu) and rare earth (Ce) ions in ZnO nanoparticles that increase the antiferromagnetic ordering to achieve high-T{sub c} ferromagnetism. Rietveld refinement of XRD patterns indicate that the dopant ions in ZnO had a wurtzite structure and the dopants, Ni{sup 2+}, Cu{sup 2+}, Ce{sup 3+} ions, are highly influenced the lattice constants to induce lattice defects. The Ni, Cu, Ce ions in ZnO have nanoparticles formation than nanorods was observed in pure sample. FTIR involve some organic groups to induce lattice defects and the metal-oxygen bonding of Zn, Ni, Cu, Ce and O atoms to confirm wurtzite structure. Raman analysis evaluates the crystalline quality, structural disorder and defects in ZnO lattice with doping. Photoluminescence spectra have strong near-band-edge emission and visible emission bands responsible for defects due to oxygen vacancies. The energy band gap is calculated using Tauc relation. Room temperature ferromagnetism has been described due to bound magnetic polarons formation with Ni{sup 2+}, Cu{sup 2+}, Ce{sup 3+} ions in ZnO via oxygen vacancies. The zero field and field cooling SQUID measurement confirm the strength of antiferromagnetism in ZnO. The field cooling magnetization is studied by Curie-Weiss law that include antiferromagnetic interactions up to low temperature. The XPS spectra have involve +3/+4 oxidation states of Ce ions to influence the observed ferromagnetism. - Graphical abstract: The lattice defects/vacancies attributed by Ni and Ce ions in the wurtzite ZnO structure are responsible in high T{sub c} -ferromagnetism due to long-range magnetic interactions with cluster and spin-glass type growth. - Highlights: • Lattice defects/vacancies attributed high T{sub c} –ferromagnetism. • Transition metal and rare earth ions deform the wurtzite ZnO lattice to induce defects. • Oxygen vacancies are more favorable than Zn with Ni, Cu, Ce into ZnO. • Defects assisted long-range ferromagnetism of doped ZnO include cluster and spin-glass growth.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Dynamics and Statistical Mechanics of Rotating and non-Rotating Vortical Flows

Three projects were analyzed with the overall aim of developing a computational/analytical model for estimating values of the energy, angular momentum, enstrophy and total variation of fluid height at phase transitions between disordered and self-organized flow states in planetary atmospheres. It is believed that these transitions in equilibrium statistical mechanics models play a role in the construction of large-scale, stable structures including super-rotation in the Venusian atmosphere and the formation of the Great Red Spot on Jupiter. Exact solutions of the spherical energy-enstrophy models for rotating planetary atmospheres by Kac's method of steepest descent predicted phase transitions to super-rotating solid-body flows at high energy to enstrophy ratio for all planetary spins and to sub-rotating modes if the planetary spin is large enough. These canonical statistical ensembles are well-defined for the long-range energy interactions that arise from 2D fluid flows on compact oriented manifolds such as the surface of the sphere and torus. This is because in Fourier space available through Hodge theory, the energy terms are exactly diagonalizable and hence has zero range, leading to well-defined heat baths.

Spherical Geometry↗
DOE OSTI2024

Long-lived oscillations of metastable states in neutral atom systems

Metastable states arise in a range of quantum systems and can be observed in various dynamical scenarios, including decay, bubble nucleation, and long-lived oscillations. The phenomenology of metastable states has been examined in quantum many-body systems, notably in one-dimensional (1D) ferromagnetic Ising spin systems and superfluids. Here, in this paper, we study long-lived oscillations of metastable and ground states in 1D antiferromagnetic neutral atom chains with long-range Rydberg interactions. We use a staggered local detuning field to achieve confinement. Using theoretical and numerical models, we identify novel spectral signatures of quasiparticle oscillations distinct to antiferromagnetic neutral atom systems and interpret them using a classical energy model of short-range meson repulsion. Finally, we evaluate the experimental accessibility of our proposed setup on current neutral-Atom platforms and discuss experimental feasibility and constraints.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗