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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Pressure-induced Td to 1T′ structural phase transition in WTe{sub 2}

WTe{sub 2} is provoking immense interest owing to its extraordinary properties, such as large positive magnetoresistance, pressure-driven superconductivity and possible type-II Weyl semimetal state. Here we report results of high-pressure synchrotron X-ray diffraction (XRD), Raman and electrical transport measurements on WTe{sub 2}. Both the XRD and Raman results reveal a structural transition upon compression, starting at 6.0 GPa and completing above 15.5 GPa. We have determined that the high-pressure lattice symmetry is monoclinic 1T′ with space group of P2{sub 1}/m. This transition is related to a lateral sliding of adjacent Te-W-Te layers and results in a collapse of the unit cell volume by ∼20.5%. The structural transition also casts a pressure range with the broadened superconducting transition, where the zero resistance disappears.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Phase transitions and the piezoelectricity around morphotropic phase boundary in Ba(Zr{sub 0.2}Ti{sub 0.8})O{sub 3}-x(Ba{sub 0.7}Ca{sub 0.3})TiO{sub 3} lead-free solid solution

In this paper, two displacive phase transitions around the morphotropic phase boundary (MPB) in Ba(Zr{sub 0.2}Ti{sub 0.8})O{sub 3}-x(Ba{sub 0.7}Ca{sub 0.3})TiO{sub 3} (BZT-xBCT) ceramics were detected by inspecting two anomalies of the Raman Ti{sup 4+}-O{sup 2−} longitudinal optical mode (∼725 cm{sup −1}). Further, permittivity and X-ray diffraction results demonstrated these two phase transitions originate from tetragonal (T) to rhombohedral (R) through an intermediate orthorhombic (O) phase. Importantly, we found that the maximum piezoelectric response (d{sub 33} = 545pC/N) was achieved at the boundary between the T and O phase, indicating that the giant piezoelectricity of BZT-xBCT may mainly stem from the T-O phase boundary due to easier polarization rotation and larger lattice softening.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

LeWRON: Agentic Analysis of Electroweak Phase Transitions

The electroweak phase transition (EWPT) is a central topic in particle physics and cosmology, connecting collider phenomenology, baryogenesis, and gravitational-wave observatories. Its analysis requires a technically demanding, convention-sensitive, and model-dependent pipeline, from constructing the finite-temperature effective potential to tracking thermal histories, computing bubble nucleation rates, and predicting gravitational-wave spectra. We present LeWRON (Learning ElectroWeak phase tRansitiON), an agentic framework that orchestrates this pipeline starting from an input Lagrangian. LeWRON combines audited toolbox construction with an Explorer module that uses the generated model-specific code for further analysis, including scans and plots. Intermediate analytic outputs are checked by auditor agents and stored as structured artifacts, enabling reproducible human inspection and downstream use through both a command-line interface and a public Python API. The framework supports a reproduction mode, which infers conventions from the literature and reproduces published results, and a discovery mode, which guides users through structured checkpoints for new models. We demonstrate LeWRON across representative beyond-the-Standard-Model scenarios and release the code on GitHub.

Wang, Isaac R. [Fermilab] (ORCID:000000030789218X)↗
DOE OSTI2016

Effective Hamiltonians for correlated narrow energy band systems and magnetic insulators: Role of spin-orbit interactions in metal-insulator transitions and magnetic phase transitions

Using a second-quantized many-electron Hamiltonian, we obtain (a) an effective Hamiltonian suitable for materials whose electronic properties are governed by a set of strongly correlated bands in a narrow energy range and (b) an effective spin-only Hamiltonian for magnetic materials. The present Hamiltonians faithfully include phonon and spin-related interactions as well as the external fields to study the electromagnetic response properties of complex materials and they, in appropriate limits, reduce to the model Hamiltonians due to Hubbard and Heisenberg. With the Hamiltonian for narrow-band strongly correlated materials, we show that the spin-orbit interaction provides a mechanism for metal-insulator transition, which is distinct from the Mott-Hubbard (driven by the electron correlation) and the Anderson mechanism (driven by the disorder). Next, with the spin-only Hamiltonian, we demonstrate the spin-orbit interaction to be a reason for the existence of antiferromagnetic phase in materials which are characterized by a positive isotropic spin-exchange energy. This is distinct from the Néel-VanVleck-Anderson paradigm which posits a negative spin-exchange for the existence of antiferromagnetism. We also find that the Néel temperature increases as the absolute value of the spin-orbit coupling increases.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Transient activation of AMP-activated protein kinase at G1/S phase transition is required for control of S phase in NIH3T3 cells

Highlights: • AMPK is transiently activated at G1/S phase of NIH3T3 cell cycle. • Temporal activation of AMPK is required for control of S phase. • AMPK activation at G1/S phase depends on intracellular calcium and CaMKKbeta. AMP-activated protein kinase (AMPK) functions as a cellular energy sensor by monitoring the cellular AMP:ATP ratio and plays a central role in cellular and whole-body energy homeostasis. Recent studies have suggested that AMPK also contribute to cell cycle regulation, but its role in this field remains almost elusive. In the present study, we report that AMPKα1 was transiently activated during G{sub 1}/S transition phase in NIH3T3 cells in the absence of any metabolic stress. Inhibition of AMPK activity at G{sub 1}/S transition phase completely blocked cells from entering S phase; in contrast, persistent activation of AMPK at G{sub 1}/S transition phase allowed cells to normally enter S phase, but these cells failed to proceed to G{sub 2}/M phase, stacking at S phase. We further demonstrated that activation of AMPK at G{sub 1}/S transition phase depends on Ca{sup 2+} transients and CaMKKβ activity, but not on energy status. Collectively, these data indicate that temporal regulation of AMPK is required for proper control of S phase in NIH3T3 cells.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2020

Proximity Spin–Orbit Torque on a Two-Dimensional Magnet within van der Waals Heterostructure: Current-Driven Antiferromagnet-to-Ferromagnet Reversible Nonequilibrium Phase Transition in Bilayer CrI 3

The recently discovered two-dimensional magnetic insulator CrI 3 is an intriguing case for basic research and spintronic applications since it is a ferromagnet in the bulk but an antiferromagnet in bilayer form, with its magnetic ordering amenable to external manipulations. Using the first-principles quantum transport approach, we predict that injecting unpolarized charge current parallel to the interface of the bilayer-CrI 3 /monolayer-TaSe 2 van der Waals (vdW) heterostructure will induce spin–orbit torque and thereby drive the dynamics of magnetization on the first monolayer of CrI 3 in direct contact with TaSe 2 . By combining the calculated complex angular dependence of spin–orbit torque with the Landau-Lifshitz-Gilbert equation for classical dynamics of magnetization, we demonstrate that current pulses can switch the direction of magnetization on the first monolayer to become parallel to that of the second monolayer, thereby converting CrI 3 from antiferromagnet to ferromagnet while not requiring any external magnetic field. We explain the mechanism of this reversible current-driven nonequilibrium phase transition by showing that first monolayer of CrI 3 carries current due to evanescent wave functions injected by metallic transition metal dichalcogenide TaSe 2 , while concurrently acquiring strong spin–orbit coupling via such a proximity effect, whereas the second monolayer of CrI 3 remains insulating. Furthermore, the transition can be detected by passing vertical read current through the vdW heterostructure, encapsulated by a bilayer of hexagonal boron nitride and sandwiched between graphite electrodes, where we find a tunneling magnetoresistance of ≃240%.

2D magnetic materials↗
DOE OSTI2019

Magnetostructural phase transitions and large magnetic entropy changes in Ag-doped Mn 1–x Ag x CoGe intermetallic compounds

The influence of Ag-doping on the crystallographic structure, magnetic properties, and magnetocaloric effects of Mn 1–x Ag x CoGe (0.01 ≤ x ≤ 0.10) is reported. A transformation of crystal structure from orthorhombic to hexagonal was observed at room temperature. Doping Ag in Mn sites results in a first-order magnetostructural transition near room temperature. Furthermore, a Curie-temperature window of 90 K was obtained between the Curie temperatures of the austenite (Ni 2 In-type) and martensite (TiNiSi-type) phases. Large magnetic entropy change values of ~22.0 and 9.4 J/kg/K, and refrigerant capacity of 308 and 272 J/kg, were found for x = 0.06 and 0.05, respectively, for μ o ΔH = 5 T.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2018

Solid–Liquid Phase Transition in the Octadecanoic Acid Film Adsorbed on the Toluene–Water Interface

The structure of the soluble protonated (pH = 2) octadecanoic acid film adsorbed on the saturated hydrocarbon (n-hexane)–water and aromatic hydrocarbon (toluene)–water interfaces is studied by X-ray reflectometry using synchrotron radiation. The experimental data demonstrate that a solid phase of a Gibbs monolayer 26 ± 1 Å thick, in which aliphatic tails are perpendicular to the surface and the area per molecule is A = 18 ± 2 Å{sup 2}, is formed in the film at the n-hexane–water interface. The solid monolayer on the toluene–water interface in the adsorbed film melts when temperature increases, and this transition is caused by disordering of the hydrocarbon tails of the acid. During the solid–liquid transition, the Gibbs monolayer thickness remains almost the same, 22 ± 1 Å. In the solid phase, we have A = 20 ± 2 Å{sup 2}, and the angle of deviation of the molecular tails from the normal to the surface is about 30°. The density of the liquid monolayer phase with A = 24 ± 2 Å{sup 2} corresponds to liquid n-octadecane.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Time-Reversal Symmetry-Breaking Nematic Insulators near Quantum Spin Hall Phase Transitions

We study the phase diagram of a model quantum spin Hall system as a function of band inversion and band-coupling strength, demonstrating that when band hybridization is weak, an interaction-induced nematic insulator state emerges over a wide range of band inversion. This property is a consequence of the long-range Coulomb interaction, which favors interband phase coherence that is weakly dependent on momentum and therefore frustrated by the single-particle Hamiltonian at the band inversion point. For weak band hybridization, interactions convert the continuous gap closing topological phase transition at inversion into a pair of continuous phase transitions bounding a state with broken time-reversal and rotational symmetries. At intermediate band hybridization, the topological phase transition proceeds instead via a quantum anomalous Hall insulator state, whereas at strong hybridization interactions play no role. We comment on the implications of our findings for InAs/GaSb and HgTe/CdTe quantum spin Hall systems.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗