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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Uniaxial Spin Texture in a Superconducting Electron Gas Revealed by Exchange Interactions

Two-dimensional (2D) superconductors with spin-textured Fermi surfaces can be a platform for realizing unconventional pairing states and are of substantial interest in the context of quantum information science and superconducting spintronics/orbitronics. We observed an unusual in-plane uniaxial anisotropy in the superconducting 2D electron gas (2DEG) formed at EuOx/KTaO3 (110) interfaces. This anisotropy is not evident in AlOx/KTaO3 (110) where the overlayer is nonmagnetic. Our results are consistent with a highly anisotropic “half-Rashba” spin-textured Fermi surface in 2DEGs formed at the KTaO3 (110) interface that is hidden from external magnetic fields due to a near cancellation between orbital and spin moments but revealed by exchange interactions of the electrons in the 2DEG with Eu moments near the EuOx/KTaO3 (110) interface. The interactions between the uniaxial spin texture and the magnetic overlayer offer previously unexplored ways to explore the interplay between magnetism and 2D superconductivity.

Yang, Junyi↗
NASA NTRS1990

Infrared spectra of van de Waals complexes of importance in planetary atmospheres

It has been suggested that (CO2)2 and Ar-CO2 are important constituents of the planetary atmospheres of Venus and Mars. Recent results on the laboratory spectroscopy of CO2 containing van der Waals complexes which may be of use in the modeling of the spectra of planetary atmospheres are presented. Sub-Doppler infrared spectra were obtained for (CO2)2, (CO2)3, and rare-gas-CO2 complexes in the vicinity of the CO2 Fermi diad at 2.7 micrometers using a color-center-laser optothermal spectrometer. From the spectroscopic constants the geometries of the complexes have been determined and van der Waals vibrational frequencies have been estimated. The equilibrium configurations are C2h, C3h, and C2v, for (CO2)2, (CO2)3, and the rare-gas-CO2 complexes, respectively. Most of the homogeneous linewidths for the revibrational transitions range from 0.5 to 22 MHz, indicating that predissociation is as much as four orders of magnitude faster than radiative processes for vibrational relaxation in these complexes.

Fraser, G. T.↗
DOE OSTI2022

Gas and Cosmic-Ray Properties in the MBM 53, 54, and 55 Molecular Clouds and the Pegasus Loops Revealed by H i Line Profiles, Dust, and Gamma-Ray Data

In studying the interstellar medium (ISM) and Galactic cosmic rays (CRs), uncertainty of the interstellar gas density has always been an issue. To overcome this difficulty, we used a component decomposition of the 21 cm H i emission line and used the resulting gas maps in an analysis of γ-ray data obtained by the Fermi Large Area Telescope (LAT) for the MBM 53, 54, and 55 molecular clouds and the Pegasus loop. We decomposed the ISM gas into intermediate-velocity clouds, narrow-line and optically thick H i, broad-line and optically thin H i, CO-bright H 2 , and CO-dark H 2 using detailed correlations with the H i line profiles from the HI4PI survey, the Planck dust-emission model, and the Fermi-LAT γ-ray data. We found the fractions of the optical depth correction to the H i column density and CO-dark H 2 to be nearly equal. We fitted the CR spectra directly measured at/near the Earth and the measured γ-ray emissivity spectrum simultaneously. We obtained a spectral break in the interstellar proton spectrum at ~7 GeV, and found that the γ-ray emissivity normalization agrees with the AMS-02 proton spectrum within 10%, relaxing the tension with the CR spectra previously claimed.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Static Self-Energy and Effective Mass of the Homogeneous Electron Gas from Quantum Monte Carlo Calculations

We discuss the methodology of quantum Monte Carlo calculations of the effective mass based on the static self-energy Σ(k,0). We then use variational Monte Carlo calculations of Σ(k,0) of the homogeneous electron gas at various densities to obtain results very close to perturbative G 0 W 0 calculations for values of the density parameter 1 ≤ r s ≤ 10. Here, the obtained values for the effective mass are close to diagrammatic Monte Carlo results and disagree with previous quantum Monte Carlo calculations based on a heuristic mapping of excitation energies to those of an ideal gas.

36 MATERIALS SCIENCE↗
NASA NTRS2016

Development of the Model of Galactic Interstellar Emission for Standard Point-Source Analysis of Fermi Large Area Telescope Data

Most of the celestial gamma rays detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope originate from the interstellar medium when energetic cosmic rays interact with interstellar nucleons and photons. Conventional point-source and extended-source studies rely on the modeling of this diffuse emission for accurate characterization. Here, we describe the development of the Galactic Interstellar Emission Model (GIEM),which is the standard adopted by the LAT Collaboration and is publicly available. This model is based on a linear combination of maps for interstellar gas column density in Galactocentric annuli and for the inverse-Compton emission produced in the Galaxy. In the GIEM, we also include large-scale structures like Loop I and the Fermi bubbles. The measured gas emissivity spectra confirm that the cosmic-ray proton density decreases with Galactocentric distance beyond 5 kpc from the Galactic Center. The measurements also suggest a softening of the proton spectrum with Galactocentric distance. We observe that the Fermi bubbles have boundaries with a shape similar to a catenary at latitudes below 20deg and we observe an enhanced emission toward their base extending in the north and south Galactic directions and located within approximately 4deg of the Galactic Center.

gamma rays: diffuse background – gamma rays: gen↗
NASA NTRS2012

The Diffuse Gamma-Ray Background from Type Ia Supernovae

The origin of the diffuse extragalactic gamma-ray background (EGB) has been intensively studied but remains unsettled. Current popular source candidates include unresolved star-forming galaxies, starburst galaxies, and blazars. In this paper we calculate the EGB contribution from the interactions of cosmic rays accelerated by Type Ia supernovae, extending earlier work which only included core-collapse supernovae. We consider Type Ia events in star-forming galaxies, but also in quiescent galaxies that lack star formation. In the case of star-forming galaxies, consistently including Type Ia events makes little change to the star-forming EGB prediction, so long as both supernova types have the same cosmic-ray acceleration efficiencies in star-forming galaxies. Thus our updated EGB estimate continues to show that star-forming galaxies can represent a substantial portion of the signal measured by Fermi. In the case of quiescent galaxies, conversely, we find a wide range of possibilities for the EGB contribution. The dominant uncertainty we investigated comes from the mass in hot gas in these objects, which provides targets for cosmic rays: total gas masses are as yet poorly known, particularly at larger radii. Additionally, the EGB estimation is very sensitive to the cosmic-ray acceleration efficiency and confinement, especially in quiescent galaxies. In the most optimistic allowed scenarios, quiescent galaxies can be an important source of the EGB. In this case, star-forming galaxies and quiescent galaxies together will dominate the EGB and leave little room for other contributions. If other sources, such as blazars, are found to have important contributions to the EGB, then either the gas mass or cosmic-ray content of quiescent galaxies must be significantly lower than in their star-forming counterparts. In any case, improved Fermi EGB measurements will provide important constraints on hot gas and cosmic rays in quiescent galaxies.

Lien, Amy↗
DOE OSTI2023

Disentangling the Hadronic Components in NGC 1068

The recent detection of high-energy neutrinos by IceCube in the direction of the nearby Seyfert/starburst galaxy NGC 1068 implies that radio-quiet active galactic nuclei can accelerate cosmic-ray ions. Dedicated multimessenger analyses suggest that the interaction of these high-energy ions with ambient gas or photons happens in a region of the galaxy that is highly opaque for GeV–TeV gamma rays. Otherwise, the GeV–TeV emission would violate existing constraints provided by the Fermi Large Area Telescope (LAT) and the Major Atmospheric Gamma Imaging Cherenkov. The conditions of high optical depth are realized near the central supermassive black hole (SMBH). At the same time, the GeV emission detected by the Fermi LAT is likely related to the galaxy’s sustained star formation activity. In this work, we derive a 20 MeV–1 TeV spectrum of NGC 1068 using 14 yr of Fermi LAT observations. We find that the starburst hadronic component is responsible for NGC 1068's emission above ~500 MeV. However, below this energy, an additional component is required. In the 20–500 MeV range, the Fermi LAT data are consistent with hadronic emission initiated by non-thermal ions interacting with gas or photons in the vicinity of the central SMBH. This highlights the importance of the MeV band to discover hidden cosmic-ray accelerators.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Dynamical defects in a two-dimensional Wigner crystal: Self-doping and kinetic magnetism

We study the quantum dynamics of interstitials and vacancies in a two-dimensional Wigner crystal (WC) using a semi-classical instanton method that is asymptotically exact at low density, i.e., in the r s → ∞ limit. Here, the dynamics of these point defects mediates magnetism with much higher energy scales than the exchange energies of the pure WC. Via exact diagonalization of the derived effective Hamiltonians in the single-defect sectors, we find the dynamical corrections to the defect energies. The resulting expression for the interstitial (vacancy) energy extrapolates to 0 at r s = r mit ≈ 70 (r s ≈ 30), suggestive of a self-doping instability to a partially melted WC for some range of r s below r mit . We thus propose a “metallic electron crystal” phase of the two-dimensional electron gas at intermediate densities between a low density insulating WC and a high density Fermi fluid.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1978

Fermi acceleration and the structure of interstellar turbulence

Recent observations at length scales of at least about 10 to the 18th cm and about 10 to the 11th cm suggest the possibility of a generally turbulent interstellar gas with a Kolmogorov spectrum. The total r.m.s. fluctuation in fluid properties is of the same order as the mean. The consequences of such a turbulence spectrum for cosmic rays are discussed. If the turbulence is composed of Alfven waves propagating in both directions along the average magnetic field, the rate of Fermi acceleration is found to be significant. Consequences of the turbulence for spatial transport and the general dynamics of the interstellar gas, as well as possible energy sources for the turbulence, are discussed. It is concluded that Fermi acceleration by interstellar turbulence is a possible acceleration mechanism for galactic cosmic rays.

Jokipii, J. R.↗
NASA NTRS1974

Possible evidence for structured acceleration of cosmic rays on a galactic scale from recent gamma-ray observations

Recent data from SAS-2 on the galactic gamma-ray line flux as a function of longitude reveal a broad maximum in the region below 30 deg. These data, as unfolded here, imply that the low-energy (1-10 GeV) galactic cosmic-ray flux varies with the radial distance from the galactic center and is about an order of magnitude higher than the local value in a toroidal region for radial distances between 4 and 5 kpc. We further show that this enhancement can be plausibly accounted for by Fermi acceleration and compression caused by a hydrodynamic shock driven by the expanding gas in the 3-kpc arm and invoked in some versions of galactic structure theory.

Stecker, F. W.↗
DOE OSTI2020

Scattering of electron from a disk in 2D electron gas: Full cross section, transport cross section, and the interaction correction

It is known that the presence of the Fermi sea modifies the scattering of an electron from a point-like impurity. This is due to the Friedel oscillations of the electron density around the impurity. These oscillations create an additional scattering potential for incident electrons. The closer the energy of the incident electron to the Fermi level, the stronger the additional scattering. Here, we study this effect for the case when the impurity is not point-like but rather a hard disk, with a radius much bigger than the de Broglie wavelength. We start with a careful examination of the full and transport cross sections from an extended target. Both cross sections approach their limiting values upon increasing the wave vector of the incident electron. We establish that the transport cross section saturates much faster than the full cross section. With regard to the interaction correction, we establish that it vanishes for the full cross section, while for the transport cross section, it is enhanced compared to the case of a point-like scatterer.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Diagrammatic Monte Carlo Approach to Real‐frequency Response Functions and the Spin‐Fermion Model of Hot Spots (Final Report)

This three‐year research project was focused on two outstanding condensed matter problems (i) Real‐frequency response functions in Coulomb systems at finite temperature, and Fermi surface (FS) reconstruction in the Spin-Fermion (SF) model. The uniform electron gas (jellium) model, describing electrons interacting via long‐range Coulomb forces on positive neutralizing background, is fundamentally important both for understanding the physics of correlated electrons and for formulation of the time‐dependent density functional theory (TDDFT). The spin-fermion model has found a wide range of applications in the physics of cuprates and iron‐based superconductors to explain the “strange metal" behavior and to suggest a possible pairing mechanism for high‐temperature superconductivity. The project’s goals were development and application of the Diagrammatic Monte Carlo (DiagMC) techniques for solving the above problems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRSDate not supplied

Electron Screened and Enhanced Nuclear Reactions

In 1954, Salpeter calculated nuclear reaction rates would increase via weak and strong electron screening in stars. Astrophysical observations and laboratory astrophysics experiments have confirmed that electron screening reduces the Coulomb Barrier between charged particles. Fermi degenerate strong screening occurs when the electron density exceeds 10e23 electrons/cm3 in the cores of gas giant planets, White Dwarf Stars, the conduction bands of metals, deuterated LENR materials and Inertial Confinement Fusion targets at maximum compression. We have modelled these quantum mechanical effects with Density Functional Theory codes.

electron screening↗
DOE OSTI2022

High-resolution laser-induced fluorescence spectroscopy of 28 Si 16 O + and 29 Si 16 O + in a cryogenic buffer-gas cell

Here, the electronic, laser-induced fluorescence spectrum of the B 2 Σ + ← X 2 Σ + transition in 28 Si 16 O + and 29 Si 16 O + has been recorded in a cryogenic buffer gas cell at K. Molecular constants are extracted for both 28 Si 16 O + and 29 Si 16 O + , including the Fermi contact hyperfine constant for both the B and X states of 29 Si 16 O + , and used in a discussion of the suitability of SiO in future quantum information experiments.

47 OTHER INSTRUMENTATION↗
DOE OSTI2022

Removal of Bond Sodium from Full-Length Unirradiated Fermi-1 Blanket Elements and Assembly via Melt-Drain-Evaporate Process

Equipment was designed, fabricated, tested, and operated in an inert atmosphere radiological glovebox at Idaho National Laboratory to demonstrate the removal of bond sodium from full-length unirradiated Fermi-1 radial blanket elements and an entire radial blanket assembly using a Melt-Drain-Evaporate process. A series of three runs was performed with individual and multiple radial Fermi-1 blanket elements, and a fourth run was conducted with an entire Fermi-1 radial blanket assembly. After each run, the depleted uranium alloy slugs in every element slid out of its cladding, mechanically exhibiting the effectual absence of bond sodium. Quantitative and further qualitative analyses of the treated Fermi-1 material revealed the substantive, if not complete, absence of sodium metal in blanket element components. Indeed, entire columns of depleted uranium alloy slugs and associated cladding from select treated elements were separately contacted with water to react with residual sodium metal on the element surfaces, forming hydrogen gas. Samples of the resultant gas were analyzed to quantify the hydrogen concentration, which correlated to a residual sodium metal content for the treated element. Accordingly, no detectable sodium metal (<7 µg) was found on the surfaces of multiple depleted uranium alloy slugs after removal from its cladding. Detectable sodium metal, ranging from 14 to 30 µg, was found on the surfaces of one separated column of slugs and two separated full-length cladding segments. Each element originally contained ~25 g of bond sodium, resulting in quantitative sodium metal removal efficiencies of =99.9998%. The remaining separated uranium alloy slugs and cladding segments from the four runs were piece-wise immersed in alcohol while videorecording possible gas bubble formation as an additional qualitative analysis for residual sodium metal on treated surfaces, which identified the predominant absence of sodium reactivity on the balance of treated Fermi-1 blanket material. The results of this demonstration substantiate a path forward for treatment and disposal of 34 metric tons heavy metal of irradiated sodium-bonded Fermi-1 blanket material currently stored at Idaho National Laboratory.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2021

Temperature effects in spin-dependent Hall currents in an ideal skyrmion gas

The quest of novel reliable and fast performing logic and memory elements in classical and quantum computing requires discoveries of new effects in novel quantum materials. Skyrmions are such magnetic textures where electron scattering can essentially change the shape and location of the skyrmion, which can be used as a memory element being more efficient than domain walls as memory device in classical computing. Because the skyrmion motion is sensitive even to very small currents, we study electron scattering by skyrmions in an ideal skyrmion gas in ferromagnetic environment. In such systems, the direct and Hall currents become spin-dependent. For applications it is important to consider a Hall effect in the whole range of temperatures under the assumption of the skyrmion existence. In this study we find the nonmonotonic temperature dependence of the direct spin-up conductivity, i. e., the conductivity for the current directed along the applied electric field due to the electrons with the spin parallel to the ferromagnetic moment. Such a behavior contradicts the traditional understanding where the temperature only increases the value of the conductivity. The spin-down Hall conductivity is found to be even more dramatic exhibiting the conductivity sign change (i.e., the change in the current direction) with temperature for small skyrmion sizes. The found effects strongly depend on Fermi energy. The most pronounced dependencies take place if the Fermi energy is slightly below and above the bottom of the upper (spin-down) energy band of an ideal 2D electron gas. In addition, we also find that the direct and Hall resistivities, ρ xx and ρ xy , are independent of the exchange integral J for 2J > ε F .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2013

Shock Heating of the Merging Galaxy Cluster A521

A521 is an interacting galaxy cluster located at z = 0.247, hosting a low-frequency radio halo connected to an eastern radio relic. Previous Chandra observations hinted at the presence of an X-ray brightness edge at the position of the relic, which may be a shock front. We analyze a deep observation of A521 recently performed with XMM-Newton in order to probe the cluster structure up to the outermost regions covered by the radio emission. The cluster atmosphere exhibits various brightness and temperature anisotropies. In particular, two cluster cores appear to be separated by two cold fronts. We find two shock fronts, one that was suggested by Chandra and that is propagating to the east, and another to the southwestern cluster outskirt. The two main interacting clusters appear to be separated by a shock-heated region, which exhibits a spatial correlation with the radio halo. The outer edge of the radio relic coincides spatially with a shock front, suggesting that this shock is responsible for the generation of cosmic-ray electrons in the relic. The propagation direction and Mach number of the shock front derived from the gas density jump, M = 2.4 +/- 0.2, are consistent with expectations from the radio spectral index, under the assumption of Fermi I acceleration mechanism.

Bourdin, H.↗
NASA NTRS2011

The Unresolved Star-Forming Galaxy Component of the Extragalactic Gamma Ray Background

We present new theoretical estimates of the contribution of unresolved star-forming galaxies to the extragalactic gamma-ray background (EGB) as measured by EGRET and the Fermi-LAT. We employ several methods for determining the star-forming galaxy contribution the the EGB, including a method positing a correlation between the gamma-ray luminosity of a galaxy and its rate of star formation as calculated from the total infrared luminosity, and a method that makes use of a model of the evolution of the galaxy gas mass with cosmic time. We find that depending on the model, unresolved star-forming galaxies could contribute significantly to the EGB as measured by the Fermi-LAT at energies between approx. 300 MeV and approx. few GeV. However, the overall spectrum of unresolved star-forming galaxies can explain neither the EGRET EGB spectrum at energies between 50 and 200 MeV nor the Fermi-LAT EGB spectrum at energies above approx. few GeV.

Venters, Tonia M.↗