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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 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Preliminary Work Toward a Transuranic Activity Estimation Method for Rapid Discrimination of Anthropogenic from Transuranic Activity in Alpha Air Samples

Radon ( 222 Rn) and thoron ( 220 Rn) progeny (primarily bismuth and polonium) are known interferents when rapid evaluation of transuranic content on air filters is of interest. These complexities stem from the overlapping energies of the progeny alpha particles onto the transuranic region of interest (3–5.5 MeV) where naturally-occurring alpha emitters can overwhelm the spectra. Due to the immediacy of the alpha counting methods employed, coupled with the half-life of thoron progeny dominated by 212 Pb (t 1/2 =10.6 h), a conservative transuranic activity estimate with rigorous uncertainty is being sought. A successful transuranic activity estimation method will incorporate any thoron progeny present on the filter providing 95% confidence decision levels in which a filter may be evaluated for emergency response applications. Twenty-three pairs of samples of various duration having no transuranic content were taken over a 2-mo period. The resulting filters were counted in a time series before non-linear least squares decay curve fitting was applied to the decay profile. For the samples considered, a transuranic activity estima-tor decision level was determined at 0.2 Bq for the given geographic location and months analyzed. In conclusion, validation of this method for other seasonal and geographic regions could provide enhanced emergency response capability when the presence of transuranic activity is suspected.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Low-temperature breakdown of many-body perturbation theory for thermodynamics

It is shown analytically and numerically that the finite-temperature many-body perturbation theory in the grand canonical ensemble has zero radius of convergence at zero temperature when the energy ordering or degree of degeneracy for the ground state changes with the perturbation strength. When the degeneracy of the reference state is partially or fully lifted at the first-order Hirschfelder-Certain degenerate perturbation theory, the grand potential and internal energy diverge as T → 0. Contrary to earlier suggestions of renormalizability by the chemical potential μ, this nonconvergence, first suspected by W. Kohn and J. M. Luttinger, is caused by the nonanalytic nature of the Boltzmann factor e –E/k e T at T = 0, also plaguing the canonical ensemble, which does not involve chemical potential. The finding reveals a fundamental flaw in perturbation theory, which is deeply rooted in the mathematical limitation of power-series expansions and is unlikely to be removed within its framework.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2011

Cold-atom gravimetry with a Bose-Einstein condensate

We present a cold-atom gravimeter operating with a sample of Bose-condensed {sup 87}Rb atoms. Using a Mach-Zehnder configuration with the two arms separated by a two-photon Bragg transition, we observe interference fringes with a visibility of (83{+-}6)% at T=3 ms. We exploit large momentum transfer (LMT) beam splitting to increase the enclosed space-time area of the interferometer using higher-order Bragg transitions and Bloch oscillations. We also compare fringes from condensed and thermal sources and observe a reduced visibility of (58{+-}4)% for the thermal source. We suspect the loss in visibility is caused partly by wave-front aberrations, to which the thermal source is more susceptible due to its larger transverse momentum spread. Finally, we discuss briefly the potential advantages of using a coherent atomic source for LMT, and we present a simple mean-field model to demonstrate that with currently available experimental parameters, interaction-induced dephasing will not limit the sensitivity of inertial measurements using freely falling, coherent atomic sources.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Deviation from Debye-Waller behavior in single crystalline freestanding Ni⁢ O membranes studied via ultrafast electron diffraction

Here, we realize single-crystal freestanding Ni⁢O films on Si⁢N membranes, enabling thin-film scattering experiments with little or no substrate background signal. These membrane samples provide a critical platform for performing ultrafast electron diffraction (UED) to probe the response of the lattice to laser excitation. We show that epitaxial Ni⁢O films on a water-soluble Sr 2 ⁢Ca⁢Al 2⁢ O 6 buffer layer on Sr⁢Ti⁢O 3 substrates can be transferred as freestanding films to the Si⁢N membranes while maintaining the epitaxial character of the films. An above-gap photoexcitation (𝜆 =266 nm) incident on the sample stimulates an initial lattice response of the order of 1.1 ps, followed by the persistence of this state for more than 20 ps. We observe typical Debye-Waller behavior in peaks with 𝑞 above the (220) family, but a distinct deviation from this behavior is seen in low-𝑞 peaks. We relate this behavior to a dynamic decrease in sample mosaicity in response to the optical pump of the order of 3% that endures for approximately 4 ps. We suspect that this dynamic mosaicity is due to laser-induced strain propagation. This work demonstrates the viability of the thin-film transfer method for UED and paves the way for the study of the dynamic response of antiferromagnetic thin-film oxides.

Wisser, Jacob J. [Stanford Univ., CA (United State↗
DOE OSTI2019

Rethinking CO adsorption on transition-metal surfaces: Effect of density-driven self-interaction errors

Adsorption of the molecule CO on metallic surfaces is an important unsolved problem in Kohn-Sham density functional theory (KS-DFT). We present a detailed study of carbon monoxide adsorption on fcc (111) surfaces of 3d, 4d, and 5d metals using nonempirical semilocal density functionals for the exchange-correlation energy: the local-density approximation (LDA), two generalized gradient approximations or GGAs [Perdew-Burke-Ernzerhof (PBE) and PBE for solids (PBEsol)], and a meta-GGA [strongly constrained and appropriately normed (SCAN) functional]. The typical error pattern (as found earlier for free molecules and for free transition-metal surfaces), in which results improve from LDA to PBE or PBEsol to SCAN, due to the satisfaction of more exact constraints, is not found here. Instead, for CO adsorption on transition-metal surfaces, we find that, while SCAN overbinds much less than LDA, it overbinds slightly more than PBE. Moreover, the tested functionals often predict the wrong adsorption site, as first pointed out for LDA and GGA in the CO/Pt (111) puzzle. This abnormal pattern leads us to suspect that the errors of PBE and SCAN for this problem are density-driven self-interaction errors associated with incorrect charge transfer between molecule and metal surface. We point out that, by the variational principle, overbinding by an approximate functional would be reduced if that functional were applied not to its self-consistent density for the adsorbed system but to an exact or more correct density for that system. Finally, we show for CO on Pt(111) that the site preference is corrected and the adsorption energy is improved for the PBE functional by using not the self-consistent PBE density but a PBE+U density. The resulting correction to the PBE total energy is much larger for the adsorbed system than for its desorbed components, showing that the error is in the density of the adsorbed system. Furthermore, this seems to solve the Feibelman 2001 CO/Pt(111) puzzle, in principle if not fully in practice.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Fluctuating Ru trimer precursor to a two-stage electronic transition in RuP

Superconductivity in binary ruthenium pnictides occurs proximal to and upon suppression of a non-magnetic ground state, preceded by a pseudogap phase associated with Fermi surface instability, and its critical temperature, T c , is maximized around the pseudogap quantum critical point. By analogy with isoelectronic iron based counterparts, antiferromagnetic fluctuations became ''usual suspects" as putative mediators of superconducting pairing. Here we report on a high temperature local symmetry breaking in RuP, nonsuperconducting parent of the maximum- T c branch of these novel superconductors, revealed by combined nanostructure-sensitive powder and single crystal X-ray total scattering analyses. Large local distortions of Ru chains associated with orbital-charge trimerization, further assembled into hexamers, exist above the two-stage electronic transition in RuP. In the pseudogap regime the precursors order with distortions retaining their strength, whereas they acquire spin-singlet characteristics which dramatically enhances the distortion as the nonmagnetic ground state establishes. The precursors enable the nonmagnetic ground state and presumed complex oligomerization, and the relevance of pseudogap fluctuations for superconductivity emerges as a distinct prospect. As a transition metal system in which partial d-manifold filling combined with high crystal symmetry promotes electronic instabilities, this represents a further example of local electronic precursors underpinning the macroscopic collective behavior of quantum materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Molecular beam epitaxy synthesis and electrical transport properties of the correlated kagome metal Ni⁢ 3 In

Ni 3 ⁢In is a paramagnetic intermetallic consisting of 𝐴⁢𝐵-stacked Ni-kagome networks. Correlated electron behaviors deviating from the Fermi-liquid form have recently been observed in Ni 3 ⁢In bulk single crystals, attributed to stabilization of a partially flat electronic band near the Fermi level. Synthesis of this system in thin-film form offers unique opportunities for tuning of materials that could aid in identifying the microscopic origin of the non-Fermi-liquid response and exploring the suspected quantum criticality therein. Here, we report the realization of (001)-oriented epitaxial thin films of Ni 3 ⁢In on single-crystal SrTiO 3 (111) substrates by molecular beam epitaxy. Via control of growth conditions, we fabricate high-quality films with quantum fluctuations strongly influencing the physical properties of the system. Analysis of the electrical transport response reveals that intrinsic spin fluctuations in Ni 3 ⁢In may account for the observed non-Fermi-liquid behavior. Such structures may facilitate driving Ni 3 ⁢In across a potential quantum critical phase transition and uncover the role of unusual flat bands in triggering correlated phenomena.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

High-pressure structural behavior of silicon telluride Si2Te3 nanoplates

The high-pressure behavior of silicon telluride (Si2Te3), a two-dimensional (2D) layered material, was investigated using synchrotron x-ray powder diffraction in a diamond anvil cell to 11.5GPa coupled with first-principles theory. Si2Te3 undergoes a phase transition at <1GPa from a trigonal to a hexagonal crystal structure. At higher pressures (>8.5GPa), x-ray diffraction showed the appearance of new peaks possibly coincident with a new phase transition, though we suspect Si2Te3 retains a hexagonal structure. Density functional theory calculations of the band structure reveal metallization above 9.1GPa consistent with previous measurements of the Raman spectra and disappearance of color and transparency at pressure. The theoretical Raman spectra reproduce the prominent features of the experiment, though a deeper analysis suggests that the orientation of Si dimers dramatically influences the vibrational response. Given the complex structure of Si2Te3, simulation of the resulting high-pressure phase is complicated by disordered vacancies and the initial orientations of Si–Si dimers in the crushed layered phase.

Li, Bohan↗
DOE OSTI2025

Weak localization as a probe of intervalley coherence in graphene multilayers

Spontaneous intervalley coherence is suspected in several different graphene multilayer systems, but is difficult to confirm because of a paucity of convenient experimental signatures. Here we suggest that magneto-conductance features associated with quantum corrections to Drude conductivity can serve as a smoking gun for intervalley coherence that does not break time-reversal symmetry. In this class of ordered multilayer quantum transport corrections can produce weak localization or weak antilocalization, depending on whether the valley order belongs to the orthogonal or symplectic symmetry class. Our analysis motivates low-temperature weak-field magnetoresistance measurements in graphene multilayers in which time-reversal invariant intervalley coherent order is conjectured.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Experimental study of the valence band of Bi 2 Se 3

The valence band of Bi 2 Se 3 is investigated with Shubnikov - de Haas measurements, galvanomagnetic and thermoelectric transport. At low hole concentration, the hole Fermi surface is closed and box-like, but at higher concentrations it develops tube-like extensions that are open. The experimentally determined density-of-states effective mass is lighter than density-functional theory calculations predict; while we cannot give a definitive explanation for this, we suspect that the theory may lack sufficient precision to compute room-temperature transport properties, such as the Seebeck coefficient, in solids in which there are Van der Waals interlayer bonds.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Cu nuclear magnetic resonance study of charge and spin stripe order in La 1.875 Ba 0.125 CuO 4

In this paper, we present a Cu nuclear magnetic/quadrupole resonance study of the charge stripe ordered phase of LBCO, with detection of previously unobserved (“wiped-out”) signal. We show that spin-spin and spin-lattice relaxation rates are strongly enhanced in the charge ordered phase, explaining the apparent signal decrease in earlier investigations. The enhancement is caused by magnetic, rather than charge fluctuations, conclusively confirming the long-suspected assumption that spin fluctuations are responsible for the wipeout effect. Observation of the full Cu signal enables insight into the spin and charge dynamics of the stripe-ordered phase, and measurements in external magnetic fields provide information on the nature and suppression of spin fluctuations associated with charge order. Lastly, we find glassy spin dynamics, in agreement with previous work, and incommensurate static charge order with charge modulation amplitude similar to other cuprate compounds, suggesting that the amplitude of charge stripes is universal in the cuprates.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Structure of Nd 155 and Gd 163 from Cf 252 spontaneous fission

Background: A puzzle has arisen recently caused by the apparent shift in maximum deformation from the expected 66 Dy isotopic chain to the Nd 60 isotopic chain in the 82 155 Nd and 163 Gd, useful for constraining parameters in models that seek to answer the six proton shift in maximum deformation. Method: Data from the spontaneous fission of 252 Cf were taken by the Gammasphere detector array at Lawrence Berkeley National Laboratory to observe the excited states of 155 Nd and 163 Gd. Results: The structure of 163 Gd has been expanded with the addition of two new levels and three new γ rays, which are found to be consistent with previously published calculations and the structure of 165 Dy. In 155 Nd, nine new levels and 12 new γ rays are observed. The spins and parities of the previously known levels in 155 Nd have been reassigned from a ν3/2 - [521] ground state configuration to a ν5/2 + [642] isomeric configuration by comparison of these newly observed levels with levels in 153 Nd and 155 Sm. Conclusion: Further experimentation is required to determine the energy of the newly reassigned ν5/2+[642] level in 155 Nd with respect to the suspected ν3/2-[521] ground state. Additionally, more experiments should be conducted to further determine the structure of neutron rich nuclei, rarely produced in the spontaneous fission of 252 Cf, such as 163 Gd.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Experimental study of the nature of the 1 – and 2 – excited states in 10 Be using the 11 Be (p,d) reaction in inverse kinematics

In this paper, we investigated the structure of two excited states in the nucleus 10 Be, which were suspected to have spatially extended wave functions (or "haloes"). This was done by performing a transfer reaction that removed a neutron from the core of the 11 Be nucleus, a well-known one-neutron halo nucleus. By doing so, we specifically produced configurations, whereas the halo neutron in 11 Be remained when populating excited states in 10 Be. If the two excited states in 10 Be had a strong overlap with those configurations, one would have expected them to be strongly populated in the reaction. We find that this was not quite the case and we postulated that the reason why was because those states had a mixed configuration that not only displayed halo-like, but also cluster-like, properties. The overlap was therefore not as strong as expected (and suggested by previous experiments).

6 ≤ A ≤ 19↗
DOE OSTI2021

Distinguishing time clustering of astrophysical bursts

Many astrophysical bursts can recur, and their time series structure or pattern could be closely tied to the emission and system physics. While analysis of periodic events is well established, some sources, e.g., some fast radio bursts and soft gamma-ray emitters, are suspected of more subtle and less explored periodic windowed behavior: the bursts themselves are not periodic, but the activity only occurs during periodic windows. Here, we focus on distinguishing periodic windowed behavior from merely clustered events through time clustering analysis, using techniques analogous to spatial clustering, demonstrating methods for identifying and characterizing the behavior. An important aspect is accounting for the “curious incident of the dog in the night time”—lack of bursts carries information. As a worked example, we analyze six years of data from the soft gamma repeater SGR 1935 + 2154 , deriving a window period of 231 days and 55% duty cycle.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Statistics of baryon correlation functions in lattice QCD

A systematic analysis of the structure of single-baryon correlation functions calculated with lattice QCD is performed, with a particular focus on characterizing the structure of the noise associated with quantum fluctuations. The signal-to-noise problem in these correlation functions is shown, as long suspected, to result from a sign problem. The log-magnitude and complex phase are found to be approximately described by normal and wrapped normal distributions respectively. Properties of circular statistics are used to understand the emergence of a large time noise region where standard energy measurements are unreliable. Power-law tails in the distribution of baryon correlation functions, associated with stable distributions and “Lévy flights,” are found to play a central role in their time evolution. A new method of analyzing correlation functions is considered for which the signal-to-noise ratio of energy measurements is constant, rather than exponentially degrading, with increasing source-sink separation time. This new method includes an additional systematic uncertainty that can be removed by performing an extrapolation, and the signal-to-noise problem reemerges in the statistics of this extrapolation. It is demonstrated that this new method allows accurate results for the nucleon mass to be extracted from the large-time noise region inaccessible to standard methods. The observations presented here are expected to apply to quantum Monte Carlo calculations more generally. Similar methods to those introduced here may lead to practical improvements in analysis of noisier systems.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Substantial crystalline topology in amorphous silicon.

Using electron correlograph analysis we show that coherent nanodiffraction patterns from sputtered amorphous silicon indicate that there is more local crystallinity in unannealed amorphous silicon than was previously suspected. By comparing with simulations for various models we show that within a typical unannealed amorphous silicon film a substantial volume fraction (>50%) is topologically crystalline with correlation lengths up to 2 nm. Electron correlograph analysis is a variant of the fluctuation electron microscopy technique and its sensitivity to local crystalline ordering is derived from its sensitivity to four-body correlations.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗