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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 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Near-half-metallic state in the half-Heusler PtMnSb film on a III-V substrate

The interplay between half-metallic ferromagnetism and spin-orbit coupling within the inversion-symmetry-broken structure of half Heuslers provides an ideal platform for various spintronics functionalities. Taking advantage of good lattice matching, it is highly desired to epitaxially integrate promising Heuslers into III-V semiconductor-based devices. PtMnSb is one of the first half Heuslers predicted to be an above-room-temperature half-metal with large spin orbit coupling, however, its half-metallicity and potential as a spintronics material has remained elusive due to lack of high quality samples. Here, in this study, we demonstrate epitaxial growth of single crystal PtMnSb(001) film on GaSb(001) substrates using molecular beam epitaxy. Direct observation of the band structure via angle-resolved photoemission spectroscopy and many-body perturbation theory within the quasi-particle self-consistent GW approximation (QPGW) reveal that PtMnSb hosts rather a near-half-metallic state with both spin bands crossing the Fermi level and with high spin polarization over 90%. Temperature dependence of magnetization also shows an anomalous enhancement below 60 K, which can be associated with the development of such a near-half-metallic state at low temperatures. Epitaxial growth of high crystalline PtMnSb on a III-V paves the way for systematic clarification of its spin transport properties with fine-tuning of strain in heterostructure devices.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Electronic structure of a nodal line semimetal candidate TbSbTe

The 𝐿⁢𝑛⁢SbTe (𝐿⁢𝑛 = Lanthanides) family, like isostructural ZrSiS-type compounds, has emerged as a fertile playground for exploring the interaction of electronic correlations and magnetic ordering with the nodal line band topology. Here, we report on a detailed electronic band structure investigation of TbSbTe, corroborated by electrical transport, thermodynamic, and magnetic studies. Temperature-dependent magnetic susceptibility and thermodynamic transport studies indicate the onset of antiferromagnetic ordering below 𝑇 𝑁 ∼ 5.8K. The electronic band structure study, carried out with high-resolution angle-resolved photoemission spectroscopy measurements aided with density functional theory–based first-principles calculations reveal presence of a nonsymmorphic symmetry-protected Dirac crossing in the Γ-X high-symmetry (HS) direction, which is part of a nodal line along the X-R HS direction. Another Dirac crossing occurs along the Γ-X direction at a relatively higher binding energy, which occurs from $\tilde{𝒞}$ 2⁢𝜈⁢ 𝒫 symmetry which is gapped in the theoretical calculations with the effect of spin-orbit coupling considered. Parallel to this direction, our theoretical calculations and experimental results exhibit strongly momentum-dependent surface bands. In this study, we open an avenue to further uncover the intricate interplay among symmetry-protected topological band structure, spin-orbit coupling, and magnetism in this material and the 𝐿⁢𝑛⁢SbTe family, in general.

Angle-resolved photoemission spectroscopy↗
DOE OSTI2024

Exploiting universal nonlocal dispersion in optically active materials for spectro-polarimetric computational imaging

Recent years have seen significant advancements in exploring novel light-matter interactions such as hyperbolic dispersion within natural crystals. However, current studies have predominantly concentrated on local optical response of materials characterized by a dielectric tensor without spatial dispersion. Here, we investigate the nonlocal response in optically-active crystals with screw symmetries, revealing their lossless, super-dispersive properties compared to traditional optical response functions. We leverage this universal nonlocal dispersion, i.e. the dispersion of optical rotatory power, to explore a novel spectral de-multiplexing scheme compared to conventional gratings, prisms and metasurfaces. We design and demonstrate an ‘Nonlocal-Cam’ - a camera that exploits nonlocal dispersion through sampling of polarized spectral states and the application of computational spectral reconstruction algorithms. The Nonlocal-Cam captures information in both laboratory and outdoor field experiments which is unavailable to traditional intensity cameras - the spectral texture of polarization. Merging the fields of nonlocal electrodynamics and computational imaging, our work paves the way for exploiting nonlocal optics of optically active materials in a variety of applications, from biological microscopy to physics-driven machine vision and remote sensing.

Wang, Xueji [Purdue Univ., West Lafayette, IN (Uni↗
NASA NTRS1988

The discrete correlation function: A new method for analyzing unevenly sampled variability data

A method of measuring correlation functions without interpolating in the temporal domain, the discrete correlation function, is introduced. It provides an assumption-free representation of the correlation measured in the data, and allows meaningful error estimates. This method does not produce spurious correlations at zero lag due to correlated errors. It is shown that physical interpretation of active galactic nuclei cross-correlation functions requires knowledge of the input function's fluctuation power spectrum, involves model-dependence in the form of symmetry assumptions, and must take into account intrinsic scale bias. This technique was used to find a correlation in published IUE data for NGC 4151, which indicates that the broad C IV feature emanates from a shell 15 to 75 light-days in radius, assuming spherical symmetry.

Edelson, R. A.↗
NASA NTRS1988

High spatial resolution 10 micron imaging of IRC + 10216

Precise high-resolution 10-micron images of the carbon star IRC + 10216 have been obtained with a scanned linear array. The low noise and high dynamic range of these images permit deconvolution of the telescope point-spread function, revealing the radial brightness distribution of the circumstellar dust shell: approximate reflection symmetry is found in west-east scans, with a distinct division into two components of diameter about 0.40 and 2.2 arcsec. It is shown that this morphology is consistent with published interferometric data that had cast doubt upon an earlier, idealized two-component model. The observed brightness distribution implies that the circumstellar dust density may deviate substantially from the 1/r squared radial dependence expected for spherically symmetric outflow with constant velocity and constant rate of mass loss.

Bloemhof, E. E.↗
NASA NTRS2010

Modeling Optical Properties of Mineral Aerosol Particles by Using Nonsymmetric Hexahedra

We explore the use of nonsymmetric geometries to simulate the single-scattering properties of airborne dust particles with complicated morphologies. Specifically, the shapes of irregular dust particles are assumed to be nonsymmetric hexahedra defined by using the Monte Carlo method. A combination of the discrete dipole approximation method and an improved geometric optics method is employed to compute the single-scattering properties of dust particles for size parameters ranging from 0.5 to 3000. The primary optical effect of eliminating the geometric symmetry of regular hexahedra is to smooth the scattering features in the phase function and to decrease the backscatter. The optical properties of the nonsymmetric hexahedra are used to mimic the laboratory measurements. It is demonstrated that a relatively close agreement can be achieved by using only one shape of nonsymmetric hexahedra. The agreement between the theoretical results and their measurement counterparts can be further improved by using a mixture of nonsymmetric hexahedra. It is also shown that the hexahedron model is much more appropriate than the "equivalent sphere" model for simulating the optical properties of dust particles, particularly, in the case of the elements of the phase matrix that associated with the polarization state of scattered light.

Bi, Lei↗
DOE OSTI2020

MEASUREMENT OF Fn 2 /Fp 2 FROM DEEP INELASTIC ELECTRON SCATTERING OFF A=3 MIRROR NUCLEI AT JEFFERSON LAB

This research is part of the Je?erson Lab MARATHON experiment (MeAsurement of the Fn 2 /Fp 2 , d/u RAtios and A = 3 EMC E?ect in Deep Inelastic Electron Scattering Off the Tritium and Helium MirrOr Nuclei). MARATHON is an experiment on electron deep inelastic scattering off the 3H, 3He mirror nuclei. It has extracted, from the measured deep inelastic scattering cross section ratio o? 3H and 3He, the ratio of the neutron to proton inelastic structure functions Fn 2 /Fp 2 . The extraction has taken advantage of the isospin symmetry of the A = 3 mirror nuclei within a novel technique, which avoids the theoretical uncertainties that are present in the SLAC experiments of the 1970s, which used hydrogen and deuterium targets. The experiment was performed using the upgraded 11 GeV beam of the Jefferson Lab electron accelerator, the Hall A Experimental Facility, and a newly designed cryogenic, high-pressure gas target system containing 3H and 3He cells. Electrons scattered o? the gas targets were detected in the two superconducting, high-resolution magnetic spectrometers of Hall A. The cross section data cover the four-momentum transfer squared range 2.0 < Q2 < 14.0 (GeV/c)2, and the Bjorken x scaling variable range 0.19 < x < 0.83. The experiment also measured, for calibration purposes, electron deep inelastic scattering off hydrogen and deuterium at selected kinematics.

Su, Tong↗
DOE OSTI2023

Interplay of broken symmetry and delocalized excitations in the insulating state of 1 T –Ta⁢S 2

Coexistence of localized and extended excitations is central to the macroscopic properties of correlated materials. For 5⁢d transition-metal compounds, electron correlations alone generally do not lead to a metal-insulator (Mott) transition, with insulating behavior usually resulting from their coupling with magnetic ordering and/or structural distortions. 1⁢T–Ta⁢S 2 is a prototypical example of such correlated insulating behavior, with a high-symmetry metallic phase transforming into a distorted, charge-density wave (CDW) insulating state at low temperatures. The nature of the insulating phase as well as the existence and relevance of the localized electron physics remains debated. We resolve this standing controversy in 1⁢T–Ta⁢S 2 combining resonant inelastic x-ray spectroscopy and first-principles calculations. We observe five electronic excitations arising from the interband transitions of the Ta 5d orbitals and the S 3⁢p ligand state, with none of the excitations on the order of the Mott gap. These excitations cannot be explained within the framework of standard multiplet calculations that assume a localized wave function, but instead, are captured by a band-theory framework accounting for the low symmetry of the crystal field in the CDW state. Our findings suggest that the electronic properties of 1T–Ta⁢S 2 are dominated in the visible by both plasmonic quasiparticles and interband transitions, with no resonance associated with a putative Mott transition observed in the 0–3 eV energy range. Finally, our discovery provides insights into the electron localization and the Mott vs band-insulator debate in 1T–Ta⁢S 2 and other transition-metal materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

The emergence of valency in colloidal crystals through electron equivalents

Colloidal crystal engineering of complex, low-symmetry architectures is challenging when isotropic building blocks are assembled. In this study we describe an approach to generating such structures based upon programmable atom equivalents (nanoparticles functionalized with many DNA strands) and mobile electron equivalents (small particles functionalized with a low number of DNA strands complementary to the programmable atom equivalents). Under appropriate conditions, the spatial distribution of the electron equivalents breaks the symmetry of isotropic programmable atom equivalents, akin to the anisotropic distribution of valence electrons or coordination sites around a metal atom, leading to a set of well-defined coordination geometries and access to three new low-symmetry crystalline phases. All three phases represent the first examples of colloidal crystals, with two of them having elemental analogues (body-centred tetragonal and high-pressure gallium), while the third (triple double-gyroid structure) has no known natural equivalent. This approach enables the creation of complex, low-symmetry colloidal crystals that might find use in various technologies.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Weyl semimetal in the rare-earth hexaboride family supporting a pseudonodal surface and a giant anomalous Hall effect

Rare-earth hexaborides offer a rich tapestry for exploring the interplay of topological orders, magnetism, and electron-correlation effects associated with protected quantum phenomena. Using first-principles modeling, we identify in cerium hexaboride (CeB 6 ) a topological state that harbors a pseudonodal surface (PNS) along with double-Weyl fermions. An analysis of the electronic states in the vicinity of the Fermi level reveals the presence of M z -mirror-symmetry-protected band crossings that involve itinerant (d) and localized (f) states of Ce. These band crossings are found to remain nearly gapless as one goes away from the mirror plane, driving the formation of PNS states. We also demonstrate the presence of coexisting double-Weyl fermions with chiral charges of ±2 on the C 4z rotational axis. By analyzing the Berry curvature field associated with the topological states, we predict that CeB 6 supports a giant anomalous Hall conductivity of -1840Ω -1 cm -1 in the slightly electron-doped regime, which would be larger than the values reported to date in magnetic Weyl semimetals. Our study thus indicates that CeB 6 , which combines ferromagnetic order with topological physics in a heavy-fermion matrix, would provide a promising playground for investigating topological magnetic states with giant anomalous Hall responses.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Information Content of the Parity-Violating Asymmetry in Pb 208

The parity-violating asymmetry A PV in 208 Pb, recently measured by the PREX-2 Collaboration, is studied using modern relativistic (covariant) and nonrelativistic energy density functionals. We first assess the theoretical uncertainty on A PV which is intrinsic to the adopted approach. To this end, we use quantified functionals that are able to accommodate our previous knowledge on nuclear observables such as binding energies, charge radii, and the dipole polarizability α D of 208 Pb. We then add the quantified value of A PV together with α D to our calibration dataset to optimize new functionals. Based on these results, we predict a neutron skin thickness in 208 Pb r skin = 0.19 ± 0.02 fm and the symmetry-energy slope L = 54 ± 8 MeV. These values are consistent with other estimates based on astrophysical data and are significantly lower than those recently reported using a particular set of relativistic energy density functionals. Here, we also make a prediction for the A PV value in 48 Ca that will be soon available from the CREX measurement.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Structure constants in $ \mathcal{N} $ = 4 SYM at finite coupling as worldsheet g-function

We develop a novel nonperturbative approach to a class of three-point functions in planar $ \mathcal{N} $ N = 4 SYM based on Thermodynamic Bethe Ansatz (TBA). More specifically, we study three-point functions of a non-BPS single-trace operator and two determinant operators dual to maximal Giant Graviton D-branes in AdS 5 × S 5 . They correspond to disk one-point functions on the worldsheet and admit a simpler and more powerful integrability description than the standard single-trace three-point functions. We first introduce two new methods to efficiently compute such correlators at weak coupling; one based on large N collective fields, which provides an example of open-closed-open duality discussed by Gopakumar, and the other based on combinatorics. The results so obtained exhibit a simple determinant structure and indicate that the correlator can be interpreted as a generalization of g -functions in 2d QFT; an overlap between an integrable boundary state and a state corresponding to the single-trace operator. We then determine the boundary state at finite coupling using the symmetry, the crossing equation and the boundary Yang-Baxter equation. With the resulting boundary state, we derive the ground-state g -function based on TBA and conjecture its generalization to other states. This is the first fully nonperturbative proposal for the structure constants of operators of finite length. The results are tested extensively at weak and strong couplings. Finally, we point out that determinant operators can provide better probes of sub-AdS locality than single-trace operators and discuss possible applications.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Phonons in complex twisted crystals: Angular momenta, interactions, and topology

We report phonons and their interactions are critically important for a variety of energy-relevant applications ranging from low thermal resistance substrates to thermal barrier coatings. Fundamental insights into the nature of phonons and allowed interactions are governed by the underlying symmetries of the crystal lattice. In this paper, we provide a comprehensive and detailed description of lattice dynamics derived from twist symmetries of chiral and achiral crystals—twist dynamics. Phonon bands naturally carry quantized crystal angular momentum derived from rotational phases, which give insights into the nature of band crossings and avoided crossings, selection rules for phonon interactions, and topological band crossing behaviors. Twist dynamics is demonstrated for a variety of materials covering a range of space groups, symmetry operations, twist axis orientations, and constituent elements. Furthermore, twist symmetry offers insights into peculiar features observed in scattering measurements. In this context, we present inelastic neutron scattering measurements for rutile TiO 2 and explain them using twist dynamics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Enhanced Interface-Driven Perpendicular Magnetic Anisotropy by Symmetry Control in Oxide Superlattices

Perpendicular magnetic anisotropy (PMA) has recently been shown to emerge at interfaces of 3d and 5d transition-metal oxides (TMOs). However, strategies to systematically stabilize such interface-driven PMA still remains elusive, hindering further applications of this design approach. Here, tuning crystal symmetry is shown to be an effective means to engineer this interfacial phenomenon. The evolution of PMA strength as a function of ferromagnetic oxide thickness quantitatively reveals the competition between volume- and interface-specific contributions that determine the magnetic anisotropy. By applying different degrees of epitaxial strain, the relative contributions to PMA are modulated, clearly revealing their correlations with crystal symmetries. To be more specific, the volume anisotropy energy is found to be correlated with the tetragonal distortion of the ferromagnetic layer, while the interface anisotropy energy is mainly modulated by the octahedral tilting at the interface. With these insights, superlattices with enhanced interface-driven PMA and higher Curie temperature are realized. These findings reveal a route to engineering interface-driven PMA and associated magnetic phenomena in TMO heterostructures for future spintronic applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Prediction of low-Z collinear and noncollinear antiferromagnetic compounds having momentum-dependent spin splitting even without spin-orbit coupling

The over 60 years old Rashba-Dresselhaus effect predicts spin-orbit coupling (SOC) induced momentum-dependent spin splitting and spin polarization in materials with noncentrosymmetric structures. Strong SOC induced effects usually require high-atomic number (Z) elements such as rare-earth elements. It has recently been pointed out that antiferromagnets could hold SOC-independent spin splitting and spin polarization. In the present work we develop the spatial and magnetic symmetry conditions enabling such antiferromagnet (AFM)-induced spin splitting, dividing the 1651 magnetic space groups into seven different spin splitting prototypes (SST-1 to SST-7). This analysis places the physics of AFM spin splitting (SST-4) within the broader context of symmetry conditions that enable the more familiar forms of spin splitting, such as ferromagnetic Zeeman effect (SST-5), nonmagnetic no spin splitting (SST-6), and the nonmagnetic Rashba and Dresselhaus effects (SST-7). The AFM-induced spin splitting and spin polarization do not necessarily require breaking of inversion symmetry or the presence of SOC, hence can exist even in centrosymmetric, low-Z light element compounds, considerably broadening the material base for spin manipulations. We use the “inverse design” approach of first formulating the target property (here, spin splitting in low-Z compounds not restricted to low symmetry structures), then derive the enabling physical design principles—the magnetic symmetry conditions—to search realizable compounds that satisfy these a priori design principles. This process uncovers 422 magnetic space groups (160 centrosymmetric and 262 noncentrosymmetric) that could hold AFM-induced, SOC-independent spin splitting and spin polarization. We then search for stable compounds following such enabling symmetries. We investigate the electronic and spin structures of some selected prototype compounds by density functional theory (DFT) and find spin textures that are different than the traditional Rashba-Dresselhaus patterns and exist even in the absence of SOC effect. We provide the DFT results for all antiferromagnetic spin splitting prototypes (SST-1, SST-2, SST-3, SST-4), and concentrate on two limits of SST-4 that are particularly unusual: When spin splitting is momentum dependent (just like the Rashba effect) but is enabled in antiferromagnets even in the absence of SOC in the Hamiltonian. This includes examples of (a) centrosymmetric SST-4A compounds (e.g., orthorhombic LaMnO 3 illustrating collinear AFM, as well as cubic NiS 2 illustrating noncollinear AFM) and (b) noncentrosymmetric SST-4B compounds (e.g., rhombohedral MnTiO 3 illustrating collinear AFM and hexagonal ScMnO 3 illustrating noncollinear AFM). The symmetry design principles outlined here, along with their transformation into an inverse design material search approach and DFT verification, could open the way to their experimental examination.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Spontaneous breaking of U(1) symmetry in coupled complex SYK models

As shown in [1], two copies of the large N Majorana SYK model can produce spontaneous breaking of a Z 2 symmetry when they are coupled by appropriate quartic terms. In this paper we similarly study two copies of the complex SYK model coupled by a quartic term preserving the U(1) x U(1) symmetry. We also present a tensor counterpart of this coupled model. When the coefficient α of the quartic term lies in a certain range, the coupled large N theory is nearly conformal. We calculate the scaling dimensions of fermion bilinear operators as functions of α. We show that the operator c$^†_{1i}$c 2i , which is charged under the axial U(1) symmetry, acquires a complex dimension outside of the line of fixed points. We derive the large N Dyson-Schwinger equations and show that, outside the fixed line, this U(1) symmetry is spontaneously broken at low temperatures because this operator acquires an expectation value. We support these findings by exact diagonalizations extrapolated to large N.

1/N expansion↗
DOE OSTI2022

Free spectator nucleons in ultracentral relativistic heavy-ion collisions as a probe of neutron skin

Besides the yield ratio of free spectator neutrons produced in ultracentral 96 Zr + 96 Zr to 96 Ru + 96 Ru collisions, we propose that the yield ratio N n /N p of free spectator neutrons to protons in a single collision system at the BNL Relativistic Heavy Ion Collider or the CERN Large Hadron Collider can be a more sensitive probe of the neutron-skin thickness Δrnp and the slope parameter L of the symmetry energy. Here, the idea is demonstrated based on the proton and neutron density distributions of colliding nuclei obtained from Skyrme-Hartree-Fock-Bogolyubov calculations, and on a Glauber model that provides information of spectator matter. The final spectator particles are produced from direct emission, clusterization by a minimum spanning tree algorithm or a Wigner function approach, and deexcitation of heavy clusters by gemini. A larger Δr np associated with a larger L value increases the isospin asymmetry of spectator matter and thus leads to a larger N n /N p , especially in ultracentral collisions where the multiplicity of free nucleons are free from the uncertainties of cluster formation and deexcitation. We have further shown that the double ratio of N n /N p in isobaric collision systems or in collisions by isotopes helps to cancel the detecting efficiency for protons. Effects from nuclear deformation and electromagnetic excitation are studied, and they are found to be subdominant compared to the expected sensitivity to Δr np .

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS2001

Theoretical Investigation of Thermo-Mechanical Behavior of Carbon Nanotube-Based Composites Using the Integral Transform Method

This project uses the integral transform technique to model the problem of nanotube behavior as an axially symmetric system of shells. Assuming that the nanotube behavior can be described by the equations of elasticity, we seek a stress function x which satisfies the biharmonic equation: del(exp 4) chi = [partial deriv(r(exp 2)) + partial deriv(r) + partial deriv(z(exp 2))] chi = 0. The method of integral transformations is used to transform the differential equation. The symmetry with respect to the z-axis indicates that we only need to consider the sine transform of the stress function: X(bar)(r,zeta) = integral(from 0 to infinity) chi(r,z)sin(zeta,z) dz.

Pawloski, Janice S.↗