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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Kibble–Zurek mechanism of Ising domains

The formation of topological defects after a symmetry-breaking phase transition is an overarching phenomenon that encodes the underlying dynamics. The Kibble-Zurek mechanism (KZM) describes these non-equilibrium dynamics of second-order phase transitions and predicts a power-law relationship between the cooling rates and the density of topological defects. It has been verified as a successful model in a wide variety of physical systems, including structure formation in the early Universe and condensed-matter materials. However, it is uncertain if the KZM mechanism is also valid for topologically trivial Ising domains, one of the most common and fundamental types of domain in condensed-matter systems. Here we show that the cooling rate dependence of Ising domain density follows the KZM power law in two different three-dimensional structural Ising domains: ferro-rotation domains in NiTiO 3 and polar domains in BiTeI. However, although the KZM slope of NiTiO 3 agrees with the prediction of the 3D Ising model, the KZM slope of BiTeI exceeds the theoretical limit, providing an example of steepening KZM slope with long-range dipolar interactions. Finally, our results demonstrate the validity of KZM for Ising domains and reveal an enhancement of the power-law exponent for transitions of non-topological quantities with long-range interactions. The Kibble-Zurek mechanism is shown to apply to structural Ising domains in three-dimensional materials. Long-range interactions modify the critical exponents away from theoretical predictions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Atomic photoionization by multiple temporal pairs of slits

In this work, we study interactions between multiple temporal pairs of slits in coherent control of photoionization of S-state atoms using a pulse train of N+1 pairs evenly delayed in time by τ, in which the two pulses in a pair with a delay τ0 are counter-rotating circularly polarized. For interacting two double-slit experiments, while Ramsey interference between two identical Archimedean spirals yields pairs of principal spirals, interference of two spirals with opposite handedness does not lead to spirals, but instead to crocodile-eye-like patterns with nictares. For more than two interacting experiments, the resulting patterns turn out just to be those two reference patterns modulated by different kinds of N-dependent time-energy Fraunhofer functions exhibiting diffraction-grating-like patterns.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2025

Permanent Electride Magnets Induced by Quasi‐Atomic Non‐Nucleus‐Bound Electrons

Abstract Interstitial quasi‐atomic electrons (IQEs) in the quantized energy levels of positively charged cavities possess a substantial own magnetic moment and control the magnetism of crystalline electrides depending on the interaction with surrounding cations. However, weak spin‐orbit coupling and gentle exchange interaction restricted by the IQEs preclude a large magnetic anisotropic, remaining a challenge for a hard magnetism. It is reported that 2D [ Re 2 C] 2+ ·2e − electrides (Re = Er, Ho, Dy, and Tb) show the permanent magnetism in a ferrimagnetic ground state, mimicking the ferrites composed of magnetic sublattices with different spin polarizations. Magnetic interaction between Re‐spin lattice and IQE‐spin lattice in the [ Re 2 C] 2+ ·2e − electrides results in a large magnetocrystalline anisotropy and high coercivity, giving a maximum energy product of 15 MGOe. It is demonstrated that the spontaneous breaking of magnetic IQE‐sublattice through substitution with paramagnetic elements produces a crossover into an antiferromagnetic spin ordering of Re‐sublattice, implying that the magnetic sublattice of IQEs drives the permanent magnetism.

Hwang, Jeong Yun [Department of Materials Science ↗
DOE OSTI2024

Pseudo-neutrino versus recoil formalism for 4-body phase space and applications to nuclear decay

It is well known that the traditional treatment of radiative corrections that utilizes the “true” neutrino momentum$\overrightarrow{p}_v$ in the differential decay rate formula could lead to a ~α/π systematic error in certain observables due to the mistreatment of 4-body kinematics. Here, I investigate the theory structure of one of the proposed solutions, the “v'-formalism”, in the nonrecoil limit appropriate for neutron and nuclear β decays. I derive an elegant master formula for the 4-body phase space and use it to reanalyze the spectrum-dependent “outer” radiative corrections to the β decay of a polarized spin-half nucleus; a complete set of analytic expressions is provided for readers to straightforwardly obtain the final numerical results. Furthermore, I compare it to the “recoil formalism” where the energy of the recoil nucleus is fixed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Diffused morphotropic phase boundary in relaxor-PbTiO 3 crystals: High piezoelectricity with improved thermal stability

Solid solution ferroelectrics are the most widely used piezoelectric material for numerous electromechanical applications, including sensors, actuators, and transducers. A milestone in ferroelectric research is the discovery of the morphotropic phase boundary that was first reported in Pb(Zr x Ti 1–x )O 3 , which has been extensively solicited to improve the performance of various solid solution ferroelectrics, including those having the highest piezoelectricity known today. However, due to the inherent correlation between phase transition and thermodynamic imbalance, the efforts of building the phase boundary encounter the challenge that high performance materials are generally accompanied by property instability. In this paper, we report a comprehensive study on the crystalline symmetry and polar nano-regions in relaxor-PbTiO 3 crystals by synchrotron measurements and property characterizations. In contrast to the common belief that the morphotropic phase boundary is a narrow composition region, the morphotropic phase boundary in ternary Pb(In 1/2 Nb 1/2 )O 3 -Pb(Mg 1/3 Nb 2/3 )O 3 -PbTiO 3 is demonstrated as an extensive region covering at least 9% of the PbTiO 3 content. Such a diffused morphotropic phase boundary is associated with the intensive interaction of polar nano-regions, leading to high piezoelectricity (>1500 pC/N) with greatly improved thermal stability, where the piezoelectric variation is ~90% over the temperature range of 273–373 K, which is about a factor of 3 lower compared to its binary counterpart Pb(Mg 1/3 Nb 2/3 )O 3 -PbTiO 3 . This work sheds light on the fundamental understanding of nanoscale inhomogeneity and macroscopic symmetry in relaxor-PbTiO 3 , and successfully interlinks the structure and properties in complex solid solutions. The existence of a diffused morphotropic phase boundary is also expected to benefit other ferroic systems beyond ferroelectrics, such as ferromagnetic and multiferroic materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

Intrinsic nonlocality of spin- and polarization-resolved probabilities in strong-field quantum electrodynamics

Spin and polarization are central to precision tests of fundamental physics and for interpreting radiation from astrophysical sources and ultraintense laser-matter experiments. Here, focusing on the fundamental process of nonlinear Compton scattering, we demonstrate that a key assumption underlying current strong-field quantum electrodynamics models, i.e., that emission can be treated as an instantaneous random event sampled from a local differential rate, is inconsistent once emission angles, electron spin, and/or photon polarization are resolved. Namely, even in strictly constant and uniform fields , the resulting fully differential distribution is sign indefinite, yielding negative inferred probabilities. The physical reason is that the photon emission probability builds up over a finite length of the electron trajectory, the formation region, during which the electron direction changes by roughly the same small angle that defines the radiation cone. Therefore, we put forward a new method where we integrate over this formation region analytically to obtain a physically consistent electron spin and photon polarization model. We show that the implementation of our model is compatible with existing Monte Carlo and particle-in-cell workflows. Simulations of a GeV-class electron-laser collision accessible at current petawatt facilities and of emission in a pulsarlike magnetic field are shown to reveal spin and polarization patterns that differ even qualitatively from state-of-the-art local models. In particular, our new model predicts substantial angle-dependent circular photon polarization where the well-known collinear-emission approach yields none, and a pronounced helicity bias in the recoiling electrons absent from current predictions. These findings have direct implications for upcoming strong-field QED experiments and for interpreting polarized radiation from extreme astrophysical environments.

astrophysical electromagnetic fields↗
DOE OSTI2022

Designing strong and tunable magnetoelectric coupling in 2D trilayer heterostructures

Abstract The quest for electric-field control of nanoscale magnetic states such as skyrmions, which would impact the field of spintronics, has led to a challenging search for multiferroic materials or structures with strong magnetoelectric coupling and efficient electric-field control. Here we report a theoretical prediction that such phenomena can be realized in two-dimensional (2D) bilayer FE/PMM and trilayer FE/PMM/FE heterostructures (two-terminal and three-terminal devices), where FE is a 2D ferroelectric and PMM is a polar magnetic metal with strong spin–orbit coupling. Such a PMM has strong Dzyaloshinskii-Moriya interactions (DMI) that can generate skyrmions, while the FE can generate strong magnetoelectric coupling through polarization-polarization interactions. In trilayer heterostructures, contact to the metallic PMM layer enables multiple polarization configurations for electric-field control of skyrmions. We report density-functional-theory calculations for particular material choices that demonstrate the effectiveness of these arrangements, with the key driver being the polarization-polarization interactions between the PMM and FE layers. The present findings provide a method to achieve strong magnetoelectric coupling in the 2D limit and a new perspective for the design of related spintronics.

Materials Science↗
DOE OSTI2024

Metasurface‐Based Mueller Matrix Microscope

In conventional optical microscopes, image contrast of objects mainly results from the differences in light intensity and/or color. Muller matrix optical microscopes (MMMs), on the other hand, can provide significantly enhanced image contrast and rich information about objects by analyzing their interactions with polarized light. However, state-of-the-art MMMs are fundamentally limited by bulky and slow polarization state generators and analyzers. Here, the study demonstrates a metasurface-based MMM, i.e., Meta-MMM, which is equipped with a chip-integrated, single-shot metasurface polarization state analyzer (Meta-PSA). The Meta-MMM is featured with high-speed measurement (≈2s per Muller matrix (MM) image), superior operation stability, dual-color operation, and high measurement accuracy (measurement error 1–2%) for MM imaging. The Meta-MMM is applied to nanostructure characterization, surface morphology analysis, and discovering birefringent structures in honeybee wings. As a result, the Meta-MMMs hold the promise to revolutionize various applications from biological imaging, medical diagnosis, and material characterization to industry inspection and space exploration.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Multipole Expansion of Atomic Electron Density Fluctuation Interactions in the Density-Functional Tight-Binding Method

The accuracy of the density-functional tight-binding (DFTB) method in describing noncovalent interactions is limited due to its reliance on monopole-based spherical charge densities. In this study, we present a multipole-extended second-order DFTB (mDFTB2) method that takes into account atomic dipole and quadrupole interactions. Furthermore, we combine the multipole expansion with the monopole-based third-order contribution, resulting in the mDFTB3 method. To assess the accuracy of mDFTB2 and mDFTB3, we evaluate their performance in describing noncovalent interactions, proton transfer barriers, and dipole moments. Here, our benchmark results show promising improvements even when using the existing electronic parameters optimized for the original DFTB3 model. Both mDFTB2 and mDFTB3 outperform their monopole-based counterparts, DFTB2 and DFTB3, in terms of accuracy. While mDFTB2 and mDFTB3 perform comparably for neutral and positively charged systems, mDFTB3 exhibits superior performance over mDFTB2 when dealing with negatively charged systems and proton transfers. Overall, the incorporation of the multipole expansion significantly enhances the accuracy of the DFTB method in describing noncovalent interactions and proton transfers.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Spectral widths and Stokes shifts in InP-based quantum dots

InP-based quantum dots (QDs) have Stokes shifts and photoluminescence (PL) line widths that are larger than in II–VI semiconductor QDs with comparable exciton energies. The mechanisms responsible for these spectral characteristics are investigated in this paper. Upon comparing different semiconductors, we find the Stokes shift decreases in the following order: InP > CdTe > CdSe. We also find that the Stokes shift decreases with core size and decreases upon deposition of a ZnSe shell. We suggest that the Stokes shift is largely due to different absorption and luminescent states in the angular momentum fine structure. The energy difference between the fine structure levels, and hence the Stokes shifts, are controlled by the electron–hole exchange interaction. Luminescence polarization results are reported and are consistent with this assignment. Spectral widths are controlled by the extent of homogeneous and inhomogeneous broadening. Here, we report PL and PL excitation (PLE) spectra that facilitate assessing the roles of homogeneous and different inhomogeneous broadening mechanisms in the spectra of zinc-treated InP and InP/ZnSe/ZnS particles. There are two distinct types of inhomogeneous broadening: size inhomogeneity and core–shell interface inhomogeneity. The latter results in a distribution of core–shell band offsets and is caused by interfacial dipoles associated with In–Se or P–Zn bonding. Quantitative modeling of the spectra shows that the offset inhomogeneity is comparable to but somewhat smaller than the size inhomogeneity. The combination of these two types of inhomogeneity also explains several aspects of reversible hole trapping dynamics involving localized In 3+ /V Zn 2– impurity states in the ZnSe shells.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Unipolar light: existence, generation, propagation, and impact on microobjects

A review is presented of recent works on optical unipolar pulses, whose electric area (integral of the electric field strength over time) is nonzero, which determines the predominant direction of the electric field strength. It is shown that the existence of unipolar pulses does not contradict Maxwell’s equations, and that unipolar pulses can propagate in waveguides. It is emphasised that, along with the spectral, energy, and polarisation parameters, the electric area of short light pulses is also an important characteristic. The unidirectional action of these pulses on microobjects indicates that it is promising to develop methods for generating radiation with such properties. We disciuss methods for the generation, propagation, and interaction of unipolar light with classical and quantum systems, as well as methods for recording the electric area of light pulses. (invited paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Parity-violating inelastic electron-proton scattering at low Q 2 above the resonance region

We report the measurement of the parity-violating asymmetry for the inelastic scattering of electrons from the proton, at $Q^2 = 0.082$ GeV$^2$ and $ W = 2.23$ GeV, above the resonance region. The result $A_{\rm Inel} = - 13.5 \pm 2.0 ({\rm stat}) \pm 3.9 ({\rm syst})$ ppm agrees with theoretical calculations, and helps to validate the modeling of the $\gamma Z$ interference structure functions $F_1^{\gamma Z}$ and $F_2^{\gamma Z}$ used in those calculations, which are also used for determination of the two-boson exchange box diagram ($\Box_{\gamma Z}$) contribution to parity-violating elastic scattering measurements. A positive parity-violating asymmetry for inclusive $\pi^-$ production was observed, as well as positive beam-normal single-spin asymmetry for scattered electrons and a negative beam-normal single-spin asymmetry for inclusive $\pi^-$ production.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗