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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Ergodic and nonergodic many-body dynamics in strongly nonlinear lattices

The study of nonlinear oscillator chains in classical many-body dynamics has a storied history going back to the seminal work of Fermi et al. [Los Alamos Scientific Laboratory Report No. LA-1940, 1955 (unpublished)]. Here, we introduce a family of such systems which consist of chains of N harmonically coupled particles with the nonlinearity introduced by confining the motion of each individual particle to a box or stadium with hard walls. The stadia are arranged on a one-dimensional lattice but they individually do not have to be one dimensional, thus permitting the introduction of chaos already at the lattice scale. For the most part we study the case where the motion is entirely one dimensional. We find that the system exhibits a mixed phase space for any finite value of N . Computations of Lyapunov spectra at randomly picked phase space locations and a direct comparison between Hamiltonian evolution and phase space averages indicate that the regular regions of phase space are not significant at large system sizes. While the continuum limit of our model is itself a singular limit of the integrable sinh Gordon theory, we do not see any evidence for the kind of nonergodicity famously seen in the work of Fermi et al. Finally, we examine the chain with particles confined to two-dimensional stadia where the individual stadium is already chaotic and find a much more chaotic phase space at small system sizes.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Phonon spectra of a two-dimensional solid dusty plasma modified by two-dimensional periodic substrates

Here, phonon spectra of a two-dimensional (2D) solid dusty plasma modulated by 2D square and triangular periodic substrates are investigated using Langevin dynamical simulations. The commensurability ratio, i.e., the ratio of the number of particles to the number of potential well minima, is set to 1 or 2. The resulting phonon spectra show that propagation of waves is always suppressed due to the confinement of particles by the applied 2D periodic substrates. For a commensurability ratio of 1, the spectra indicate that all particles mainly oscillate at one specific frequency, corresponding to the harmonic oscillation frequency of one single particle inside one potential well. At a commensurability ratio of 2, the substrate allows two particles to sit inside the bottom of each potential well, and the resulting longitudinal and transverse spectra exhibit four branches in total. We find that the two moderate branches come from the harmonic oscillations of one single particle and two combined particles in the potential well. The other two branches correspond to the relative motion of the two-body structure in each potential well in the radial and azimuthal directions. The difference in the spectra between the square and triangular substrates is attributed to the anisotropy of the substrates and the resulting alignment directions of the two-body structure in each potential well.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Signatures of an energetic charged body streaming in a plasma

A charged body moving in a plasma can excite a variety of linear and nonlinear waves in the form of trailing wakes, fore-wake shocks, and precursor solitons. These structures can further interact with the background plasma to create secondary effects that can serve as signatures of the passage of the charged body. Using particle-in-cell simulations, we carry out a basic investigation of the dynamics of a plasma system that is being traversed by an energetic charged body. Using two different shapes of this charged source, namely, an idealized infinite length planar source and a two-dimensional thin rectangular source, we examine the differences in the nature of the excited wave structures and their consequent impact on the background plasma. Our simulations reveal interesting features such as the dependence of the precursor speeds on the total charge on the driving source, local particle trapping, and energization of the trapped particles in various regions along the traversal path leading to the formation of energetic charged beamlets. So our basic findings could find practical applications such as in analyzing the trajectories of charged objects like space debris orbiting in the ionosphere.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Numerical Evidence for Many-Body Localization in Two and Three Dimensions

Disorder and interactions can lead to the breakdown of statistical mechanics in certain quantum systems, a phenomenon known as many-body localization (MBL). Much of the phenomenology of MBL emerges from the existence of localized-bits, or l-bits, a set of conserved quantities that are spatially localized and binary (i.e., possess only ±1 eigenvalues). While MBL and l-bits are known to exist in one-dimensional systems, their existence in dimensions greater than one is a key open question. To tackle this question, we develop an algorithm that can find approximate binary l-bits in arbitrary dimensions by adaptively generating a basis of operators in which to represent the l-bit. We use the algorithm to study four models: the one-, two-, and three-dimensional disordered Heisenberg models and the two-dimensional disordered hard-core Bose-Hubbard model. For all four of the models studied, our algorithm finds high-quality l-bits at large disorder strength and rapid qualitative changes in the distributions of l-bits in particular ranges of disorder strengths, suggesting the existence of MBL transitions. Furthermore, these transitions in the one-dimensional Heisenberg model and two-dimensional Bose-Hubbard model coincide well with past estimates of the critical disorder strengths in these models which further validates the evidence of MBL-like behavior in the other two and three-dimensional models we examine. In addition to finding MBL-like behavior in higher dimensions, our algorithm can be used to probe MBL in various geometries and dimensionality.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Localized excitons in defective monolayer germanium selenide

Germanium selenide (GeSe) is a van der Waals–bonded layered material with promising optoelectronic properties, which has been experimentally synthesized for two-dimensional (2D) semiconductor applications. In the monolayer, due to reduced dimensionality and, thus, screening environment, perturbations such as the presence of defects have a significant impact on its properties. We apply density functional theory and many-body perturbation theory to understand the electronic and optical properties of GeSe containing a single selenium vacancy in the –2 charge state. We predict that the vacancy results in midgap “trap states” that strongly localize the electron and hole density and lead to sharp, low-energy optical absorption peaks below the predicted pristine optical gap. Analysis of the exciton wave function reveals that the 2D Wannier-Mott exciton of the pristine material monolayer is strongly modified by the presence of the defect. The lowest-energy exciton wave function is highly localized around the defect, with the Bohr radius reduced by a factor of 4 when compared to the pristine material and a dipole moment along the out-of-plane axis due to the defect-induced symmetry breaking. Altogether, these results suggest that the vacancy significantly modifies the excitonic properties of the system, demonstrating the importance of considering defects in the context of material design.

2-dimensional systems↗
DOE OSTI2021

Epitaxial stabilization of thin films of the frustrated Ge-based spinels

Frustrated magnets can host numerous exotic many-body quantum and topological phenomena. GeNi 2 O 4 is a three-dimensional S=1 frustrated magnet with an unusual two-stage transition to the two-dimensional antiferromagnetic ground state, while GeCu 2 O 4 is a high-pressure phase with a strongly tetragonally elongated spinel structure and magnetic lattice formed by S=1/2 CuO 2 linear chains with frustrated interchain exchange interactions and exotic magnetic behavior. Here, we report on the thin-film epitaxial stabilization of these two compounds. The developed growth mode, surface morphology, crystal structure, and copper valence state were characterized by in situ reflection high-energy electron diffraction, atomic force microscopy, x-ray reflectivity, x-ray diffraction, x-ray photoelectron spectroscopy, and resonant x-ray absorption spectroscopy. Our results pave an alternative route to the comprehensive investigation of the puzzling magnetic properties of these compounds and the exploration of emergent features driven by strain.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Superstructural phase transitions in polymer-grafted nanooctahedra

Superlattices of polyhedral nanocrystals exhibit emergent properties defined by their structural arrangements, but native nanocrystal ligands often limit their programmability. Polymeric ligands address this limitation by enabling tunable nanocrystal softness through modifications of polymer molecular weight and grafting density. Here, we investigate phase transitions in polymer-grafted nanooctahedra by varying polymer length, nanocrystal size, truncation, and ligand density. In two-dimensional superlattices, longer polymers or smaller nanooctahedra induce a transition from orientationally ordered to hexagonal rotator lattices. In three-dimensional superlattices, increasing polymer length drives transitions from Minkowski to body-centered cubic and plastic hexagonal close-packed phases, while higher grafting densities further enable transitions to simple hexagonal phases. Polymer brush and thermodynamic perturbation theories, supported by Monte Carlo simulations, uncover the entropic and enthalpic forces that govern these transitions. This work highlights the versatility of polymer-grafted anisotropic nanocrystals as building blocks for designing hierarchical superstructures and metamaterials with customizable properties.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Probing critical phenomena in open quantum systems using atom arrays

At continuous phase transitions, quantum many-body systems exhibit complex, emergent behavior. Most notably, at a quantum critical point, correlations decay as a power law, with exponents determined by a set of universal scaling dimensions. Experimentally probing such power law correlations is extremely challenging, owing to the interplay between decoherence, the vanishing energy gap, and boundary effects. In this work, we used a Rydberg quantum simulator to adiabatically prepare critical ground states of both a one-dimensional ring and a two-dimensional square lattice. By accounting for and tuning the openness of our quantum system, which is well-captured by a single phenomenological length scale, we directly observed power law correlations and extracted the corresponding scaling dimensions. Our work complements recent studies of quantum criticality that use the Kibble-Zurek mechanism and digital quantum circuits.

Fang, Fang [Harvard Univ., Cambridge, MA (United S↗
DOE OSTI2020

Materials Data on HoTe2ClO5 by Materials Project

HoTe2O5Cl crystallizes in the triclinic P-1 space group. The structure is two-dimensional and consists of one HoTe2O5Cl sheet oriented in the (0, 0, 1) direction. there are two inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded in a 6-coordinate geometry to six O2- and one Cl1- atom. There are a spread of Ho–O bond distances ranging from 2.28–2.36 Å. The Ho–Cl bond length is 2.88 Å. In the second Ho3+ site, Ho3+ is bonded in a distorted body-centered cubic geometry to eight O2- atoms. There are a spread of Ho–O bond distances ranging from 2.30–2.56 Å. There are four inequivalent Te4+ sites. In the first Te4+ site, Te4+ is bonded in a 4-coordinate geometry to four O2- and one Cl1- atom. There are a spread of Te–O bond distances ranging from 1.89–2.55 Å. The Te–Cl bond length is 3.20 Å. In the second Te4+ site, Te4+ is bonded in a 4-coordinate geometry to four O2- and one Cl1- atom. There are a spread of Te–O bond distances ranging from 1.89–2.59 Å. The Te–Cl bond length is 3.14 Å. In the third Te4+ site, Te4+ is bonded in a 4-coordinate geometry to four O2- and one Cl1- atom. There are a spread of Te–O bond distances ranging from 1.92–2.35 Å. The Te–Cl bond length is 3.01 Å. In the fourth Te4+ site, Te4+ is bonded in a 4-coordinate geometry to four O2- and one Cl1- atom. There are a spread of Te–O bond distances ranging from 1.91–2.36 Å. The Te–Cl bond length is 3.09 Å. There are ten inequivalent O2- sites. In the first O2- site, O2- is bonded in a bent 120 degrees geometry to two Te4+ atoms. In the second O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Ho3+ and one Te4+ atom. In the third O2- site, O2- is bonded in a distorted trigonal planar geometry to two Ho3+ and one Te4+ atom. In the fourth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two Te4+ atoms. In the fifth O2- site, O2- is bonded in a 3-coordinate geometry to one Ho3+ and two Te4+ atoms. In the sixth O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Ho3+ and one Te4+ atom. In the seventh O2- site, O2- is bonded in a 3-coordinate geometry to one Ho3+ and two Te4+ atoms. In the eighth O2- site, O2- is bonded in a distorted trigonal planar geometry to two Ho3+ and one Te4+ atom. In the ninth O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent Ho3+ and two Te4+ atoms. In the tenth O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent Ho3+ and two Te4+ atoms. There are two inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a 1-coordinate geometry to one Ho3+ atom. In the second Cl1- site, Cl1- is bonded in a 4-coordinate geometry to four Te4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LaPb6BrO7 by Materials Project

LaPb6O7Br crystallizes in the orthorhombic Cmcm space group. The structure is two-dimensional and consists of two LaPb6O7Br sheets oriented in the (0, 1, 0) direction. La3+ is bonded in a body-centered cubic geometry to eight O2- atoms. There are four shorter (2.54 Å) and four longer (2.63 Å) La–O bond lengths. There are three inequivalent Pb2+ sites. In the first Pb2+ site, Pb2+ is bonded in a 5-coordinate geometry to three O2- and two equivalent Br1- atoms. There are one shorter (2.26 Å) and two longer (2.33 Å) Pb–O bond lengths. Both Pb–Br bond lengths are 3.39 Å. In the second Pb2+ site, Pb2+ is bonded in a distorted rectangular see-saw-like geometry to four O2- atoms. There are a spread of Pb–O bond distances ranging from 2.21–2.55 Å. In the third Pb2+ site, Pb2+ is bonded in a distorted T-shaped geometry to three O2- atoms. There are two shorter (2.22 Å) and one longer (2.26 Å) Pb–O bond lengths. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded to two equivalent La3+ and two Pb2+ atoms to form a mixture of edge and corner-sharing OLa2Pb2 tetrahedra. In the second O2- site, O2- is bonded to one La3+ and three Pb2+ atoms to form a mixture of distorted edge and corner-sharing OLaPb3 tetrahedra. In the third O2- site, O2- is bonded in a distorted see-saw-like geometry to four Pb2+ atoms. Br1- is bonded in a distorted square co-planar geometry to four equivalent Pb2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ni2S by Materials Project

Ni2S crystallizes in the tetragonal I4/mmm space group. The structure is two-dimensional and consists of two Ni2S sheets oriented in the (0, 0, 1) direction. Ni1+ is bonded in a 4-coordinate geometry to four equivalent S2- atoms. All Ni–S bond lengths are 2.39 Å. S2- is bonded in a body-centered cubic geometry to eight equivalent Ni1+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ba2Ca2Tl2Sn3O10 by Materials Project

Ba2Ca2Tl2Sn3O10 crystallizes in the triclinic P1 space group. The structure is two-dimensional and consists of one Ba2Ca2Tl2Sn3O10 sheet oriented in the (0, 0, 1) direction. there are two inequivalent Ba2+ sites. In the first Ba2+ site, Ba2+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of Ba–O bond distances ranging from 2.46–3.02 Å. In the second Ba2+ site, Ba2+ is bonded to five O2- atoms to form distorted BaO5 trigonal bipyramids that share corners with four equivalent BaO5 trigonal bipyramids, corners with four equivalent SnO5 trigonal bipyramids, and edges with four equivalent BaO5 trigonal bipyramids. There are a spread of Ba–O bond distances ranging from 2.36–2.96 Å. There are two inequivalent Ca2+ sites. In the first Ca2+ site, Ca2+ is bonded in a 8-coordinate geometry to four O2- atoms. All Ca–O bond lengths are 2.40 Å. In the second Ca2+ site, Ca2+ is bonded in a body-centered cubic geometry to eight O2- atoms. There are a spread of Ca–O bond distances ranging from 2.48–2.55 Å. There are two inequivalent Tl1+ sites. In the first Tl1+ site, Tl1+ is bonded in a distorted trigonal non-coplanar geometry to three O2- atoms. There are a spread of Tl–O bond distances ranging from 2.40–2.47 Å. In the second Tl1+ site, Tl1+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Tl–O bond distances ranging from 2.57–3.42 Å. There are three inequivalent Sn+3.33+ sites. In the first Sn+3.33+ site, Sn+3.33+ is bonded to five O2- atoms to form distorted SnO5 trigonal bipyramids that share corners with four equivalent BaO5 trigonal bipyramids and corners with four equivalent SnO5 trigonal bipyramids. There are a spread of Sn–O bond distances ranging from 1.98–2.10 Å. In the second Sn+3.33+ site, Sn+3.33+ is bonded to five O2- atoms to form distorted corner-sharing SnO5 trigonal bipyramids. There are a spread of Sn–O bond distances ranging from 1.99–2.12 Å. In the third Sn+3.33+ site, Sn+3.33+ is bonded in a distorted see-saw-like geometry to four O2- atoms. There are a spread of Sn–O bond distances ranging from 2.14–2.16 Å. There are ten inequivalent O2- sites. In the first O2- site, O2- is bonded to two equivalent Ca2+ and two equivalent Sn+3.33+ atoms to form distorted corner-sharing OCa2Sn2 tetrahedra. In the second O2- site, O2- is bonded in a 1-coordinate geometry to four equivalent Ba2+, one Tl1+, and one Sn+3.33+ atom. In the third O2- site, O2- is bonded in a distorted see-saw-like geometry to two equivalent Ca2+ and two equivalent Sn+3.33+ atoms. In the fourth O2- site, O2- is bonded to one Ba2+ and five Tl1+ atoms to form a mixture of distorted edge and corner-sharing OBaTl5 octahedra. The corner-sharing octahedral tilt angles are 16°. In the fifth O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent Ca2+ and two equivalent Sn+3.33+ atoms. In the sixth O2- site, O2- is bonded to two equivalent Ca2+ and two equivalent Sn+3.33+ atoms to form a mixture of distorted edge and corner-sharing OCa2Sn2 tetrahedra. In the seventh O2- site, O2- is bonded in a 1-coordinate geometry to four equivalent Ba2+ and one Sn+3.33+ atom. In the eighth O2- site, O2- is bonded to two equivalent Ca2+ and two equivalent Sn+3.33+ atoms to form a mixture of distorted edge and corner-sharing OCa2Sn2 tetrahedra. In the ninth O2- site, O2- is bonded in a 4-coordinate geometry to one Ba2+ and three Tl1+ atoms. In the tenth O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent Ca2+ and two equivalent Sn+3.33+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TiMo3 by Materials Project

TiMo3 crystallizes in the orthorhombic Immm space group. The structure is two-dimensional and consists of two TiMo3 sheets oriented in the (0, 0, 1) direction. Ti is bonded in a distorted body-centered cubic geometry to eight Mo atoms. There are four shorter (2.73 Å) and four longer (2.79 Å) Ti–Mo bond lengths. There are two inequivalent Mo sites. In the first Mo site, Mo is bonded in a 10-coordinate geometry to two equivalent Ti atoms. In the second Mo site, Mo is bonded in a 8-coordinate geometry to four equivalent Ti atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on YFe2Bi2(SeO2)2 by Materials Project

Y(BiO2)2(FeSe)2 crystallizes in the tetragonal I4/mmm space group. The structure is two-dimensional and consists of two FeSe sheets oriented in the (0, 0, 1) direction and two Y(BiO2)2 sheets oriented in the (0, 0, 1) direction. In each FeSe sheet, Fe+2.50+ is bonded to four equivalent Se2- atoms to form a mixture of corner and edge-sharing FeSe4 tetrahedra. All Fe–Se bond lengths are 2.58 Å. Se2- is bonded in a 4-coordinate geometry to four equivalent Fe+2.50+ atoms. In each Y(BiO2)2 sheet, Y3+ is bonded in a body-centered cubic geometry to eight equivalent O2- atoms. All Y–O bond lengths are 2.41 Å. Bi2+ is bonded in a 4-coordinate geometry to four equivalent O2- atoms. All Bi–O bond lengths are 2.27 Å. O2- is bonded to two equivalent Y3+ and two equivalent Bi2+ atoms to form a mixture of corner and edge-sharing OY2Bi2 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LaScSi by Materials Project

LaScSi crystallizes in the tetragonal I4/mmm space group. The structure is two-dimensional and consists of two LaScSi sheets oriented in the (0, 0, 1) direction. La2+ is bonded in a 4-coordinate geometry to four equivalent Si4- atoms. All La–Si bond lengths are 3.14 Å. Sc2+ is bonded in a 4-coordinate geometry to four equivalent Si4- atoms. All Sc–Si bond lengths are 2.79 Å. Si4- is bonded in a body-centered cubic geometry to four equivalent La2+ and four equivalent Sc2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mg3Mn by Materials Project

Mg3Mn crystallizes in the monoclinic P2_1/m space group. The structure is two-dimensional and consists of one Mg3Mn sheet oriented in the (0, 0, 1) direction. there are three inequivalent Mg sites. In the first Mg site, Mg is bonded in a distorted bent 120 degrees geometry to two equivalent Mn atoms. There are one shorter (2.75 Å) and one longer (2.79 Å) Mg–Mn bond lengths. In the second Mg site, Mg is bonded in a distorted bent 120 degrees geometry to two equivalent Mn atoms. Both Mg–Mn bond lengths are 2.84 Å. In the third Mg site, Mg is bonded to four equivalent Mn atoms to form a mixture of distorted edge and corner-sharing MgMn4 tetrahedra. There are a spread of Mg–Mn bond distances ranging from 2.86–2.94 Å. Mn is bonded in a body-centered cubic geometry to eight Mg atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Pr2Mg by Materials Project

MgPr2 crystallizes in the monoclinic C2/m space group. The structure is two-dimensional and consists of two MgPr2 sheets oriented in the (1, 0, 0) direction. Mg is bonded in a body-centered cubic geometry to eight Pr atoms. There are a spread of Mg–Pr bond distances ranging from 3.40–3.43 Å. There are two inequivalent Pr sites. In the first Pr site, Pr is bonded in a 4-coordinate geometry to four equivalent Mg atoms. In the second Pr site, Pr is bonded in a 12-coordinate geometry to four equivalent Mg atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Adaptive variational quantum minimally entangled typical thermal states for finite temperature simulations

Scalable quantum algorithms for the simulation of quantum many-body systems in thermal equilibrium are important for predicting properties of quantum matter at finite temperatures. Here we describe and benchmark a quantum computing version of the minimally entangled typical thermal states (METTS) algorithm for which we adopt an adaptive variational approach to perform the required quantum imaginary time evolution. The algorithm, which we name AVQMETTS, dynamically generates compact and problem-specific quantum circuits, which are suitable for noisy intermediate-scale quantum (NISQ) hardware. We benchmark AVQMETTS on statevector simulators and perform thermal energy calculations of integrable and nonintegrable quantum spin models in one and two dimensions and demonstrate an approximately linear system-size scaling of the circuit complexity. We further map out the finite-temperature phase transition line of the two-dimensional transverse field Ising model. Finally, we study the impact of noise on AVQMETTS calculations using a phenomenological noise model.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗