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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Lattice flexibility in Ca 3 Ru 2 O 7 : Control of electrical transport via anisotropic magnetostriction

We report that Ca 3 Ru 2 O 7 is a correlated and spin-orbit coupled system with an extraordinary anisotropy. It is both interesting and unique largely because this material exhibits conflicting phenomena that are often utterly inconsistent with traditional precedents, particularly, the quantum oscillations in the nonmetallic state and colossal magnetoresistivity achieved by avoiding a fully spin-polarized state. This work focuses on the relationship between the lattice and transport properties along each crystalline axis and reveals that application of magnetic field, H, along different crystalline axes readily stretches or shrinks the lattice in a uniaxial manner, resulting in distinct electronic states. Furthermore, application of modest pressure drastically amplifies the anisotropic magnetoelastic effect, leading to either an occurrence of a robust metallic state at H $∥$ hard axis or a reentrance of the nonmetallic state at H $∥$ easy axis. Ca3Ru2O7 presents a rare lattice-dependent magnetotransport mechanism, in which the extraordinary lattice flexibility enables an exquisite control of the electronic state via magnetically stretching or shrinking the crystalline axes, and the spin polarization plays an unconventional role unfavorable for maximizing conductivity. At the heart of the intriguing physics is the anisotropic magnetostriction that leads to exotic states.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Examination of the cerium α-ε phase transition under dynamic loading with x-ray diffraction

Recent examination of the cerium Hugoniot with pyrometry and x-ray diffraction (XRD) has revealed a narrow solid-liquid two-phase region. It has been suggested that nonequilibrium melting may be occurring along the Ce Hugoniot, with either melt kinetics or a sluggish α-ε transition impeding the transition. In particular, the kinetics of the α-ε is unknown and the location of the phase boundary is in dispute. Static measurements suggest a nearly vertical phase boundary that intersects the Hugoniot at 6–7 GPa. This lies in direct conflict with dynamic measurements along the Hugoniot observing α-Ce through incipient melt. This work presents dynamic experiments using XRD to examine the behavior of the α-ε phase transition. The results show that the α-ε phase transition occurs through a tetragonal distortion, with the transition beginning at temperatures below the solid Hugoniot. Following the initial deviation from an ideal fcc structure, the c/a ratio is found to gradually increase with no steady value observed in the ε phase within the range of these experiments (below 17 GPa). Multiple diffraction patterns captured during the peak stress state show no significant change in c/a ratio prior to uniaxial release, upon which Ce reverts to an fcc structure. Furthermore, the results indicate that the α-ε transition occurs rapidly, both on loading and release. An examination of the c/a ratio with increasing temperatures suggests 11.5 GPa as a lower bound for the location of the α-ε-liquid triple point.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Ground state of Ce 3 Bi 4 Pd 3 unraveled by hydrostatic pressure

Noncentrosymmetric Ce 3 Bi 4 Pd 3 has attracted a lot of attention as a candidate for strongly correlated topological material, yet its experimental ground state remains a matter of contention. Two conflicting scenarios have emerged from a comparison to the prototypical Kondo insulator Ce 3 Bi 4 Pd 3 : Either Ce 3 Bi 4 Pd 3 is a spin-orbit-driven topological semimetal or a Kondo insulator with smaller Kondo coupling than its Pt counterpart. Here, we determine the ground state of Ce 3 Bi 4 Pd 3 via electrical resistivity measurements under hydrostatic pressure, which is a clean symmetry-preserving tuning parameter that increases hybridization but virtually preserves spin-orbit coupling. Ce 3 Bi 4 Pd 3 becomes more insulating under pressures up to 2.3 GPa, which is a signature of Ce-based Kondo insulating materials in the considered pressure range. Its small zero-pressure gap increases quadratically with pressure, similar to the behavior observed in the series Ce 3 Bi 4 (Pt 1 - x Pd x ) 3 , which indicates that Pt substitution and applied pressure have a similar effect. Finally, our result not only demonstrates that Kondo coupling, rather than spin-orbit coupling, is the main tuning parameter in this class of materials, but it also establishes that Ce 3 Bi 4 Pd 3 has a narrow-gap Kondo insulating ground state.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Superconducting penetration depth through a Van Hove singularity: Sr 2 ⁢RuO 4 under uniaxial stress

A plethora of experiments in Sr 2 RuO 4 have reached conflicting conclusions about the symmetry of the superconducting gap. To probe the gap’s structure in k-space, we use strain to continuously tune the band structure through a Van Hove singularity (VHS) while imaging the superconductivity with scanning SQUID microscopy. We find that the superfluid density peaks at the VHS and that the temperature dependence of the penetration depth is T 2 -quadratic over the entire measured range of strain ε. These results are consistent with a gap structure that has vertical line nodes, experimentally confirming that non-local effects in the Meissner screening can lead to T 2 behavior and clarifying the nature of the low-energy excitations in Sr 2 RuO 4 .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Indirect determination of the astrophysical S factor for the Li 6 ( p , γ ) Be 7 reaction using the asymptotic normalization coefficient method

The 6 Li(p,γ) 7 Be cross section influences a variety of astrophysical scenarios, including big-bang and stellar nucleosynthesis. In recent years, conflicting results of direct measurements have been published, reporting contradictory low-energy trends. To shed light on the contradiction between the existing data sets, the reaction was studied using the asymptotic normalization coefficient (ANC) technique which was up-to-now never used for this reaction. To derive the ANC, the 6 Li( 3 He,d) 7 Be transfer reaction, studied at the Department of Physics and Astronomy of the University of Catania and at the John. D. Fox Superconducting Accelerator Laboratory at Florida State University, was re-analyzed, focusing on the proton transfer mechanism [the α transfer process is discussed by Kiss et al. [Phys. Lett. B 807, 135606 (2020)]. Here, the energy of the 3 He beam impinging on a 6 Li target was E lab = 3 MeV and E lab = 5 MeV. The yield of the emitted deuterons was measured with high precision by using silicon ΔE – E telescopes.

6 ≤ A ≤ 19↗
DOE OSTI2022

Coupled fission fragment angular momenta

Here, nuclear fission produces fragments whose spins are coupled to the relative angular motion via angular momentum conservation. It is shown how ensembles of such spins can readily be obtained by either direct microcanonical sampling or by sampling of the associated normal modes of rotation. The resulting distribution of the spin-spin opening angle is illustrated in various three- and two-dimensional scenarios and it is demonstrated how recent mutually conflicting model calculations can be well reproduced with different assumptions about the scission geometry.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Radiative decay branching ratio of the Hoyle state

The triple-alpha process is a vital reaction in nuclear astrophysics, characterized by two consecutive reactions [2α ⇌ 8 Be (α, γ) 12 C] that drive carbon formation. The second reaction occurs through the Hoyle state, a 7.65 MeV excited state in 12 C with J π = 0 + . The rate of the process depends on the radiative width, which can be determined by measuring the branching ratio for electromagnetic decay. Recent measurements by Kibédi et al. conflicted with the adopted value and resulted in a significant increase of nearly 50% in this branching ratio, directly affecting the triple-alpha reaction. Here, this work aims to utilize charged-particle spectroscopy with magnetic selection as a means to accurately measure the total radiative branching ratio (Γ rad /Γ) of the Hoyle state in 12 C.

6 ≤ A ≤ 19↗
DOE OSTI2025

Hypertriton puzzle in relativistic heavy-ion collisions

The yields of hadrons and light nuclei in relativistic collisions of heavy-nuclei at a center of mass energy of $\sqrt{s_{NN}}$ = 2.6 TeV can be described remarkably well by a thermal distribution of an ideal gas of hadrons and light nuclei interacting only via the decay of resonances. Given the particularly small binding energy of hypertritons relative to the temperature describing the yields (about 156 MeV), one might naturally expect hypertrions to dissociate in medium, making the agreement of hypertriton yields with thermal predictions highly puzzling. The puzzle is compounded by the fact that small binding energy is associated with the large size of the hypertriton. This size is on a similar scale to the overall size of the fireball and much larger than the length scale over which temperatures in the fireball vary over phenomenologically relevant amounts. Here, this paper quantifies the tension this effect causes and shows that it is sufficiently large to render the thermal model inconsistent: its natural assumptions are in conflict with its outputs. The possibility that hypertritons are formed at freeze out as compact objects, quark droplets, that subsequently evolve into hypertritons is considered as a way to resolve the puzzle. It is noted that beyond making the assumption that compact quark droplets form, additional detailed dynamical assumptions which have not been justified are needed to make the thermal model work. The issue of why, despite these issues, the hypertriton is well described by a simple statistical description at freeze out is unresolved. Resolving the hypertriton puzzle is important as it may clarify whether the phenomenological success of the simple thermal model for yields accurately reflects the simple picture of the underlying physics on which it is based.

hydrodynamic models↗
DOE OSTI2020

Decaying sterile neutrinos and the short baseline oscillation anomalies

The MiniBooNE experiment has observed a significant excess of electron neutrinos in a muon neutrino beam, in conflict with standard neutrino oscillations. We discuss the possibility that this excess is explained by a sterile neutrino with a mass ~1 keV that decays quickly back into active neutrinos plus a new light boson. This scenario satisfies terrestrial and cosmological constraints because it has neutrino self-interactions built-in. Accommodating also the LSND, reactor, and gallium anomalies is possible, but requires an extension of the model to avoid cosmological limits.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Revisiting constraints on asymmetric dark matter from collapse in white dwarf stars

The runaway collapse phase of a small dark matter cluster inside a white dwarf star encompasses a reversible stage, where heat can be transferred back and forth between nuclear and dark matter. Induced nuclear burning phases are stable and early carbon depletion undermines previous claims of type Ia supernova ignition. Instead, mini black holes are formed at the center of the star that either evaporate or accrete stellar material until a macroscopic sub-Chandrasekhar-mass black hole is formed. In the latter case, a 0.1 to 1 second lasting electromagnetic transient signal can be detected upon ejection of the white dwarf’s potential magnetic field. Binary systems that transmute to black holes and subsequently merge emit gravitational waves. Advanced LIGO should detect one such sub-Chandrasekhar binary black hole inspiral per year, while future Einstein telescope-like facilities will detect thousands per year. The effective spin parameter distribution is peaked at 0.2 and permits future studies to disentangle from primordial sub-Chandrasekhar black holes. Such signatures are compatible with current direct detection constraints, as well as with neutron star constraints in the case of bosonic dark matter, even though they remain in conflict with the fermionic case for part of the parameter space.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Dark Energy Survey Year 3 results: Cosmological constraints from galaxy clustering and galaxy-galaxy lensing using the MagLim lens sample

The cosmological information extracted from photometric surveys is most robust when multiple probes of the large scale structure of the Universe are used. Two of the most sensitive probes are the clustering of galaxies and the tangential shear of background galaxy shapes produced by those foreground galaxies, so-called galaxy-galaxy lensing. Combining the measurements of these two two-point functions leads to cosmological constraints that are independent of the way galaxies trace matter (the galaxy bias factor). The optimal choice of foreground, or lens, galaxies is governed by the joint, but conflicting requirements to obtain accurate redshift information and large statistics. We present cosmological results from the full 5000 deg 2 of the Dark Energy Survey’s first three years of observations (Y3) combining those two-point functions, using for the first time a magnitude-limited lens sample (MagLim) of 11 million galaxies, especially selected to optimize such combination, and 100 million background shapes. We consider two flat cosmological models, the Standard Model with dark energy and cold dark matter ( Λ CDM ) a variation with a free parameter for the dark energy equation of state ( w CDM ). Both models are marginalized over 25 astrophysical and systematic nuisance parameters. In Λ CDM we obtain for the matter density Ω m = 0.320 - 0.034 + 0.041 and for the clustering amplitude S 8 ≡ σ 8 ( Ω m / 0.3 ) 0.5 = 0.778 - 0.031 + 0.037 , at 68% C.L. The latter is only 1 σ smaller than the prediction in this model informed by measurements of the cosmic microwave background by the Planck satellite. In w CDM we find Ω m = 0.32 - 0.046 + 0.044 , S 8 = 0.777 - 0.051 + 0.049 and dark energy equation of state w = - 1.031 - 0.379 + 0.218 . We find that including smaller scales, while marginalizing over nonlinear galaxy bias, improves the constraining power in the Ω m - S 8 plane by 31% and in the Ω m - w plane by 41% while yielding consistent cosmological parameters from those in the linear bias case. These results are combined with those from cosmic shear in a companion paper to present full DES-Y3 constraints from the three two-point functions ( 3 × 2 pt ).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Low- ν method with LHC neutrinos

The Forward Physics Facility (FPF) plans to use neutrinos produced at the Large Hadron Collider to make a variety of measurements at previously unexplored TeV energies. Its primary goals include precision measurements of the neutrino cross section and using the measured neutrino flux both to uncover information about far-forward hadron production and to search for various beyond standard model scenarios. However, these goals have the potential to conflict: Extracting information about the flux or cross section relies upon an assumption about the other. In this paper, we demonstrate that the FPF can use the low- ν method—a technique for constraining the flux shape by isolating neutrino interactions with low energy transfer to the nucleus—to break this degeneracy. We show that the low- ν method is effective for extracting the ν μ flux shape, in a model-independent way. We discuss its application for extracting the ν ¯ μ flux shape but find that this is significantly more model dependent. Finally, we explore the precision to which the ν μ flux shape could be constrained at the FPF for a variety of proposed detector options. We find that the precision would be sufficient to discriminate between various realistic flux models. Published by the American Physical Society 2024

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Time-Resolved XUV Opacity Measurements of Warm Dense Aluminum

The free-free opacity in plasmas is fundamental to our understanding of energy transport in stellar interiors and for inertial confinement fusion research. However, theoretical predictions in the challenging dense plasma regime are conflicting and there is a dearth of accurate experimental data to allow for direct model validation. Here we present time-resolved transmission measurements in solid-density Al heated by an XUV free-electron laser. We use a novel functional optimization approach to extract the temperaturedependent absorption coefficient directly from an oversampled pool of single-shot measurements, and find a pronounced enhancement of the opacity as the plasma is heated to temperatures of order of the Fermi energy. Plasma heating and opacity enhancement are observed on ultrafast timescales, within the duration of the femtosecond XUV pulse. We attribute further rises in the opacity on ps timescales to melt and the formation of warm dense matter

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Theoretical investigation of charge density wave instability in CuS 2

The existence of a charge density wave (CDW) in transition-metal dichalcogenide (TMDC) CuS 2 has remained undetermined since its first experimental synthesis nearly 50 years ago. Despite conflicting experimental literature regarding its low-temperature structure, there exists no theoretical investigation of the phonon properties and lattice stability of this material. By studying the first-principles electronic structure and phonon properties of CuS 2 at various electronic temperatures, we identify temperature-sensitive soft phonon modes which unveil a previously unreported Kohn anomaly at approximately 100 K. Variation of the electronic temperature shows the presence of two distinct phases, characterized at low electronic temperature by a 2 × 2 × 2 periodic charge modulation associated with the motion of the S 2 dimers. We find this is driven by a slight orbital occupation imbalance of the copper d and sulfur p orbitals, reminiscent of the Jahn-Teller effect in finite systems. Investigation of the Fermi surface presents a potential Fermi surface nesting vector related to the location of the Kohn anomaly and observed band splittings in the unfolded band structure. The combination of these results suggests a strong possibility of CDW order in CuS 2 . Further study of CuS 2 in monolayer form finds no evidence of a CDW phase, as the identified bulk periodic distortions cannot be realized in two dimensions. This behavior sets this material apart from other transition-metal dichalcogenide materials, which exhibit a charge density wave phase down to the two-dimensional limit. As CDW in TMDC materials is considered to compete with superconductivity, the lack of a CDW in monolayer CuS 2 suggests the possibility of enhanced superconductivity relative to other transition-metal dichalcogenides. Altogether, our work identifies CuS 2 as a previously unrealized candidate to study the interplay of superconductivity, CDW order, and dimensionality.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Comment on “Tunneling-tip-induced collapse of the charge gap in the excitonic insulator Ta 2 NiSe 5 ”

In this study, we investigate the discrepancy between the estimate of Q. He [], who observed a remarkable collapse of the exciton gap in Ta 2 NiSe 5 due to the electrostatic field between the scanning tunneling microscope (STM) tip and the sample, and that of a recent angle-resolved photoemission spectroscopy investigation [C. Chen , ]. It is proposed that a critical factor contributing to this discrepancy is due to He 's assumption of a constant work function of the STM tip. This assumption led to an underestimation of the tip-induced electric field. Using a literature value for the sample work function, a more substantial electric field strength is obtained, which resolves the apparent conflict between the doping estimates of these two techniques. Furthermore, our findings highlight the importance of the STM tip condition, which can significantly impact the tip work function and, consequently, influence the doping estimation in experiments involving tip-induced electric fields. Published by the American Physical Society 2024

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Near, far, wherever you are: simulations on the dose efficiency of holographic and ptychographic coherent imaging

Different studies in X-ray microscopy have arrived at conflicting conclusions about the dose efficiency of imaging modes involving the recording of intensity distributions in the near (Fresnel regime) or far (Fraunhofer regime) field downstream of a specimen. A numerical study is presented on the dose efficiency of near-field holography, near-field ptychography and far-field ptychography, where ptychography involves multiple overlapping finite-sized illumination positions. Unlike what has been reported for coherent diffraction imaging, which involves recording a single far-field diffraction pattern, it is found that all three methods offer similar image quality when using the same fluence on the specimen, with far-field ptychography offering slightly better spatial resolution and a lower mean error. These results support the concept that (if the experiment and image reconstruction are done properly) the sample can be near or far; wherever you are, photon fluence on the specimen sets one limit to spatial resolution.

42 ENGINEERING↗
DOE OSTI2021

Illustrated formalisms for total scattering data: a guide for new practitioners

The total scattering method is the simultaneous study of both the real- and reciprocal-space representations of diffraction data. While conventional Bragg-scattering analysis (employing methods such as Rietveld refinement) provides insight into the average structure of the material, pair distribution function (PDF) analysis allows for a more focused study of the local atomic arrangement of a material. Generically speaking, a PDF is generated by Fourier transforming the total measured reciprocal-space diffraction data (Bragg and diffuse) into a real-space representation. However, the details of the transformation employed and, by consequence, the resultant appearance and weighting of the real-space representation of the system can vary between different research communities. As the worldwide total scattering community continues to grow, these subtle differences in nomenclature and data representation have led to conflicting and confusing descriptions of how the PDF is defined and calculated. This paper provides a consistent derivation of many of these different forms of the PDF and the transformations required to bridge between them. Some general considerations and advice for total scattering practitioners in selecting and defining the appropriate choice of PDF in their own research are presented. This contribution aims to benefit people starting in the field or trying to compare their results with those of other researchers.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Broadband X-ray ptychography using multi-wavelength algorithm

Ptychography is a rapidly developing scanning microscopy which is able to view the internal structures of samples at a high resolution beyond the illumination size. The achieved spatial resolution is theoretically dose-limited. A broadband source can provide much higher flux compared with a monochromatic source; however, it conflicts with the necessary coherence requirements of this coherent diffraction imaging technique. In this paper, a multi-wavelength reconstruction algorithm has been developed to deal with the broad bandwidth in ptychography. Compared with the latest development of mixed-state reconstruction approach, this multi-wavelength approach is more accurate in the physical model, and also considers the spot size variation as a function of energy due to the chromatic focusing optics. Therefore, this method has been proved in both simulation and experiment to significantly improve the reconstruction when the source bandwidth, illumination size and scan step size increase. It is worth mentioning that the accurate and detailed information of the energy spectrum for the incident beam is not required in advance for the proposed method. Further, we combine multi-wavelength and mixed-state approaches to jointly solve temporal and spatial partial coherence in ptychography so that it can handle various disadvantageous experimental effects. The significant relaxation in coherence requirements by our approaches allows the use of high-flux broadband X-ray sources for high-efficient and high-resolution ptychographic imaging.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗