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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 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

A Natural 2D Heterostructure [Pb 3.1 Sb 0.9 S 4 ][Au x Te 2– x ] with Large Transverse Nonsaturating Negative Magnetoresistance and High Electron Mobility

We report the two-dimensional (2D) natural hetero-structure [Pb 3.1 Sb 0.9 S 4 ][Au$_x$Te$_{2-x}$] ($x$ = 0.52-0.36) which shows anomalous, transverse nonsaturating negative magnetoresistance (MR). For $x$ = 0.52, the material has a commensurately modulated structure with alternating [Pb3.1Sb0.9S4] rocksalt layers and atomically thin [Au$_x$Te$_{2-x}$] sheets, as determined by single-crystal X-ray diffraction using a (3 + 1)-dimensional space group; for other $x$ compositions, the modulated structure is absent and the Au and Te atoms are disordered. The transport properties in this system at low temperature (<100 K) are dominated by an unusual 2D hopping mechanism, while at room temperature a high carrier mobility of similar to ~1352 cm 2 V -1 s -1 obtained ($x$ = 0.36). The confined electrons within the [Au$_x$Te$_{2-x}$] layers are also exposed to interlayer coupling with the insulating [Pb 3.1 Sb 0.9 S 4 ] layers, and as a result, the properties of the heterostructures emerge not only from the constituent layers but also the interactions between them. Furthermore, the various Au and Te coordination patterns found in the [Au$_x$Te$_{2-x}$] sheets as a function of $x$ further contribute to a unique electronic structure that leads to the anomalous nonsaturating negative MR with different field dependent behaviors. First-principles calculations indicate that the [Au$_x$Te$_{2-x}$] sheets are responsible for the unusual electrical transport properties in this 2D system.

2D materials↗
DOE OSTI2023

Coherent correlation imaging for resolving fluctuating states of matter

Fluctuations and stochastic transitions are ubiquitous in nanometre-scale systems, especially in the presence of disorder. However, their direct observation has so far been impeded by a seemingly fundamental, signal-limited compromise between spatial and temporal resolution. Here we develop coherent correlation imaging (CCI) to overcome this dilemma. Our method begins by classifying recorded camera frames in Fourier space. Contrast and spatial resolution emerge by averaging selectively over same-state frames. Temporal resolution down to the acquisition time of a single frame arises independently from an exceptionally low misclassification rate, which we achieve by combining a correlation-based similarity metric with a modified, iterative hierarchical clustering algorithm. We apply CCI to study previously inaccessible magnetic fluctuations in a highly degenerate magnetic stripe domain state with nanometre-scale resolution. We uncover an intricate network of transitions between more than 30 discrete states. Our spatiotemporal data enable us to reconstruct the pinning energy landscape and to thereby explain the dynamics observed on a microscopic level. CCI massively expands the potential of emerging high-coherence X-ray sources and paves the way for addressing large fundamental questions such as the contribution of pinning and topology in phase transitions and the role of spin and charge order fluctuations in high-temperature superconductivity.

36 MATERIALS SCIENCE↗
DOE OSTI2015

In situ controlled heteroepitaxy of single-domain GaP on As-modified Si(100)

Metalorganic vapor phase epitaxy of III-V compounds commonly involves arsenic. We study the formation of atomically well-ordered, As-modified Si(100) surfaces and subsequent growth of GaP/Si(100) quasisubstrates in situ with reflection anisotropy spectroscopy. Surface symmetry and chemical composition are measured by low energy electron diffraction and X-ray photoelectron spectroscopy, respectively. A two-step annealing procedure of initially monohydride-terminated, (1 × 2) reconstructed Si(100) in As leads to a predominantly (1 × 2) reconstructed surface. GaP nucleation succeeds analogously to As-free systems and epilayers free of antiphase disorder may be grown subsequently. The GaP sublattice orientation, however, is inverted with respect to GaP growth on monohydride-terminated Si(100)

36 MATERIALS SCIENCE↗
DOE OSTI2025

Polariton spectra under the collective coupling regime. I. Efficient simulation of linear spectra and quantum dynamics

We outline two general theoretical techniques to simulate polariton quantum dynamics and optical spectra under the collective coupling regimes described by a Holstein–Tavis–Cummings (HTC) model Hamiltonian. The first one takes advantage of sparsity of the HTC Hamiltonian, which allows one to reduce the cost of acting polariton Hamiltonian onto a state vector to the linear order of the number of states, instead of the quadratic order. The second one is applying the well-known Chebyshev series expansion approach for quantum dynamics propagation and to simulate the polariton dynamics in the HTC system; this approach allows us to use a much larger time step for propagation and only requires a few recursive operations of the polariton Hamiltonian acting on state vectors. These two theoretical approaches are general and can be applied to any trajectory-based non-adiabatic quantum dynamics methods. We apply these two techniques with our previously developed Lindblad-partially linearized density matrix approach to simulate the linear absorption spectra of the HTC model system, with both inhomogeneous site energy disorders and dipolar orientational disorders. Our numerical results agree well with the previous analytic and numerical work.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Structures of the mitochondrial single-stranded DNA binding protein with DNA and DNA polymerase γ

Abstract The mitochondrial single-stranded DNA (ssDNA) binding protein, mtSSB or SSBP1, binds to ssDNA to prevent secondary structures of DNA that could impede downstream replication or repair processes. Clinical mutations in the SSBP1 gene have been linked to a range of mitochondrial disorders affecting nearly all organs and systems. Yet, the molecular determinants governing the interaction between mtSSB and ssDNA have remained elusive. Similarly, the structural interaction between mtSSB and other replisome components, such as the mitochondrial DNA polymerase, Polγ, has been minimally explored. Here, we determined a 1.9-Å X-ray crystallography structure of the human mtSSB bound to ssDNA. This structure uncovered two distinct DNA binding sites, a low-affinity site and a high-affinity site, confirmed through site-directed mutagenesis. The high-affinity binding site encompasses a clinically relevant residue, R38, and a highly conserved DNA base stacking residue, W84. Employing cryo-electron microscopy, we confirmed the tetrameric assembly in solution and capture its interaction with Polγ. Finally, we derived a model depicting modes of ssDNA wrapping around mtSSB and a region within Polγ that mtSSB binds.

Biochemistry & Molecular Biology↗
DOE OSTI2011

Transverse localization of light in nonlinear photonic lattices with dimensionality crossover

In a numerical study, we demonstrate the dimensionality crossover in Anderson localization of light. We consider crossover from the two-dimensional (2D) to the one-dimensional (1D) lattice, optically induced in both linear and nonlinear dielectric media. The joint influence of nonlinearity and disorder on Anderson localization in such systems is discussed in some detail. We find that, in the linear regime, the localization is more pronounced in two dimensions than in one dimension. We also find that the localization in the intermediate cases of crossover is less pronounced than in both the pure 1D and 2D cases in the linear regime, whereas in the nonlinear regime this depends on the strength of the nonlinearity. There exist strongly nonlinear regimes in which 1D localization is more pronounced than the 2D localization, opposite to the case of the linear regime. We find that the dimensionality crossover is characterized by two different localization lengths, whose behavior is different along different transverse directions.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2023

Theory of glide symmetry protected helical edge states in a WTe 2 monolayer

Helical edge states in quantum spin Hall (QSH) materials are central building blocks of topological matter design and engineering. Despite their principal topological protection against elastic backscattering, the level of operational stability depends on manifold parameters such as the band gap of the given semiconductor system in the “inverted” regime, temperature, disorder, and crystal orientation. Here, we theoretically investigate electronic and transport properties of QSH edge states in large gap 1-T' WTe 2 monolayers. We explore the impact of edge termination, disorder, temperature, and interactions on experimentally addressable edge state observables, such as local density of states and conductance. We show that conductance quantization can remain surprisingly robust even for heavily disordered samples because of an anomalously small edge state decay length and additional protection related to the large direct gap allowed by glide symmetry. From the simulation of temperature-dependent resistance, we find that moderate disorder enhances the stability of conductance by localizing bulk states. We evaluate the edge state velocity and Luttinger liquid parameter as functions of the chemical potential, finding prospects for physics beyond linear helical Luttinger liquids in samples with ultraclean and well-defined edges.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Fractional AC Josephson effect in a topological insulator proximitized by a self-formed superconductor

A lateral Josephson junction in which the surface of a 3D topological insulator serves as the weak link should support topologically protected excitations related to Majorana fermions. The resulting 4π-periodic current-phase relationship could be detected under high-frequency excitation by the suppression of odd Shapiro steps. Here, in this study, we demonstrate such devices through the self-formation of a Pd-Te superconducting layer from a telluride topological insulator, and observe suppressed first and third Shapiro steps. Other devices, including those where the Pd-Te layer is bolstered by an additional Al layer, show no suppression of Shapiro steps, a difference supported by simulations. Though we rule out the known trivial causes of suppressed Shapiro steps in our devices, we nevertheless argue that corroborating measurements and disorder-aware theoretical descriptions of these systems are needed before confidently claiming the observation of Majorana states.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

Real-space Green;s function calculations of Compton profiles

We report the development of a first-principles, real-space Green's function method for calculation of Compton profiles in the impulse approximation. For crystalline Be, we find excellent agreement with prior theoretical treatments requiring periodicity, with prior experimental measurements of the Compton profile, and with present measurements of the dynamical structure factor via nonresonant inelastic x-ray scattering (often also called x-ray Thomson scattering in the plasma physics community). We also find good agreement with prior experimental results for the Compton profile of Cu. This approach can be extended to disordered and very high-temperature systems, such as 'warm dense matter,' where theories presently used for the interpretation of inelastic x-ray scattering include condensed phase effects only at a perturbative level.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Quantum phase transition and ferromagnetism in C o 1 + x Sn

The onset of ferromagnetism in cobalt-tin alloys is investigated experimentally and theoretically. The Co 1+x Sn alloys were prepared by rapid quenching from the melt and form a modified hexagonal NiAs-type crystal structure for 0.45 ≤ x ≤ 1. The magnetic behavior is described analytically and by density-functional theory using supercells and the coherent-potential approximation. The excess of Co concentration x, which enters the interstitial 2d sites in the hypothetical NiAs-ordered parent alloy CoSn, yields a Griffiths-like phase and, above a quantum critical point (x c ≈ 0.65), a quantum phase transition to ferromagnetic order. Quantum critical exponents are determined on the paramagnetic and ferromagnetic sides of the transition and related to the nature of the magnetism in itinerant systems with different types of chemical disorder.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

Correlation effects during liquid infiltration into hydrophobic nanoporous media

To explain the thermal effects observed during the infiltration of a nonwetting liquid into a disordered nanoporous medium, we have constructed a model that includes correlation effects in a disordered medium. It is based on analytical methods of the percolation theory. The infiltration of a porous medium is considered as the infiltration of pores in an infinite cluster of interconnected pores. Using the model of randomly situated spheres (RSS), we have been able to take into account the correlation effect of the spatial arrangement and connectivity of pores in the medium. The other correlation effect of the mutual arrangement of filled and empty pores on the shell of an infinite percolation cluster of filled pores determines the infiltration fluctuation probability. This probability has been calculated analytically. Allowance for these correlation effects during infiltration and defiltration makes it possible to suggest a physical mechanism of the contact angle hysteresis and to calculate the dependences of the contact angles on the degree of infiltration, porosity of the medium, and temperature. Based on the suggested model, we have managed to describe the temperature dependences of the infiltration and defiltration pressures and the thermal effects that accompany the absorption of energy by disordered porous medium-nonwetting liquid systems with various porosities in a unified way.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Non-Enzymatic Decomposition of Collagen Fibers by a Biglycan Antibody and a Plausible Mechanism for Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a systemic autoimmune inflammatory and destructive joint disorder that affects tens of millions of people worldwide. Normal healthy joints maintain a balance between the synthesis of extracellular matrix (ECM) molecules and the proteolytic degradation of damaged ones. In the case of RA, this balance is shifted toward matrix destruction due to increased production of cleavage enzymes and the presence of (autoimmune) immunoglobulins resulting from an inflammation induced immune response. Herein we demonstrate that a polyclonal antibody against the proteoglycan biglycan (BG) causes tissue destruction that may be analogous to that of RA affected tissues. The effect of the antibody is more potent than harsh chemical and/or enzymatic treatments designed to mimic arthritis-like fibril de-polymerization. In RA cases, the immune response to inflammation causes synovial fibroblasts, monocytes and macrophages to produce cytokines and secrete matrix remodeling enzymes, whereas B cells are stimulated to produce immunoglobulins. The specific antigen that causes the RA immune response has not yet been identified, although possible candidates have been proposed, including collagen types I and II, and proteoglycans (PG's) such as biglycan. We speculate that the initiation of RA associated tissue destruction in vivo may involve a similar non-enzymatic decomposition of collagen fibrils via the immunoglobulins themselves that we observe here ex vivo.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2017

Magnetic exchange disorder in low-dimensional quantum magnets

Low-dimensional quantum magnetism is currently of great interest due to the fact that reduced dimensionality can support strong quantum fluctuations, which may lead to unusual phenomena and quantum-critical behavior. The effect of random exchange strengths in two-dimensional (2D) antiferromagnets is still not fully understood despite much effort. This project aims to rectify this by investigating the high-field properties of the 2D coordination polymer (QuinH) 2 Cu(Cl x Br 1-x ) 4 .2H 2 O. The exchange pathway is through Cu-Halide-Cu bonds, and by randomizing the proportion of chlorine and bromine atoms in the unit cell, disorder can be introduced into the system.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

National High Magnetic Field Laboratory 2016 Annual Research Report: Termination of Two-Dimensional Metallic Conduction near the Metal-Insulator Transition in Si/SiGe Quantum Wells

The physical properties of two-dimensional (2D) electrons have been a subject of interest for a long time. Yet after many years of research, the ground states of a 2D electron system (2DES) in the presence of disorder and electron-electron interaction, a realistic situation in experiments, remain an open question. Recent observations of a downturn in conductivity at low temperatures in a Si/SiGe quantum well [1], Si-MOSFETs [2,3], and 2D holes in GaAs [4-6] seem to suggest that disorder plays an important role in the so-called 2D metal-insulator transition (MIT) and at T → 0 2DES may eventually become insulating. In this experiment, we focus on the downturn behavior as a function of spin polarization, which is varied by an in-plane magnetic field.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Prediction and Control of Atomic Ordering in Electrodeposited Binary Alloy Films: Direct Synthesis of L10 Magnetic Phases

Permanent magnet materials are essential components in renewable energy technology, underlying, electric vehicles, hybrids, wind turbines and more. Today commercial permanent magnets based on Nd-Fe-B exhibit an energy product of ~ 400 kJ/m 3 , capable to run wind turbines efficiently. Unfortunately, the supplies of rare-earth elements are centralized, and their availability may see volatility over time. This state of affairs stimulates the search for the search for rare-earth-free permanent magnetic materials. The L1 0 crystal structure underlines an important class of chemical ordered alloys that exhibit uniaxial magnetocrystalline anisotropy. This material has been considered an excellent candidate for rare-earth-free permanent magnets. In this program, a series of systematic experiments were performed and analysed in order to understand the effect of each. In order to synthesize L 10-Fe-Ni, one has to circumvent the sluggish kinetic and the limited driving force resulted from the low order-disorder temperature (~320°C) of the system. A strategy was found to trigger a martensitic transformation from the FCC phase to one of the non-cubic phases by high-strain methods. The body-centered tetragonal Fe-Ni obtained by this strategy was considered as a precursor of L10 Fe-Ni. The formation of BCT Fe-Ni via a displacive process was also implemented at the nanoscale by using tailored AuNi@FeNi core@shell.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Memory formation in matter

Memory formation in matter is a theme of broad intellectual relevance; it sits at the interdisciplinary crossroads of physics, biology, chemistry, and computer science. Memory connotes the ability to encode, access, and erase signatures of past history in the state of a system. Once the system has completely relaxed to thermal equilibrium, it is no longer able to recall aspects of its evolution. The memory of initial conditions or previous training protocols will be lost. Thus many forms of memory are intrinsically tied to far-from-equilibrium behavior and to transient response to a perturbation. This general behavior arises in diverse contexts in condensed-matter physics and materials, including phase change memory, shape memory, echoes, memory effects in glasses, return-point memory in disordered magnets, as well as related contexts in computer science. Yet, as opposed to the situation in biology, there is currently no common categorization and description of the memory behavior that appears to be prevalent throughout condensed-matter systems. Here the focus is on material memories. Here, the basic phenomenology of a few of the known behaviors that can be understood as constituting a memory will be described. The hope is that this will be a guide toward developing the unifying conceptual underpinnings for a broad understanding of memory effects that appear in materials.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Unraveling the Effect of Conformational and Electronic Disorder in the Charge Transport Processes of Semiconducting Polymers

Charge transport in semiconducting polymers is inextricably linked to their microstructure, making the characterization of polymer morphology at all length-scales essential for understanding the factors that limit mobility in these materials. Indeed, charge transport depends both on the ability of polarons to delocalize at the approximately nanometer length-scale and navigate a complex energetic and morphological mesoscale landscape. While characterization of the mesoscale morphology of polymers is well-established, studies of the local chain packing and nanoscale disorder, which affect delocalization, can be significantly more difficult to carry out. Additionally, through infrared charge modulation spectroscopy and theoretical modeling, the effect of the local chain environment on polaron delocalization is directly measured and quantified. Using a series of polymers based on the model system, poly(3-hexylthiophene), the link between disorder and polaron localization is systematically explored. Polaron delocalization is correlated with known trends in mobility, revealing that while charge delocalization is always beneficial, the formation of tie-chains is necessary to reach the highest mobilities in semicrystalline polymers. The results provide direct evidence for the importance of both nanoscale (charge carrier delocalization) and mesoscale (tie-chains) orders, demonstrating the need to distinguish the key length-scale limiting charge transport in the design of new, high mobility polymers.

36 MATERIALS SCIENCE↗