Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “condensed phase systems”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Z 2 topological order and first-order quantum phase transitions in systems with combinatorial gauge symmetry

We study a generalization of the two-dimensional transverse-field Ising model, combining both ferromagnetic and antiferromagnetic two-body interactions, that hosts exact global and local Z 2 gauge symmetries. Using exact diagonalization and stochastic series expansion quantum Monte Carlo methods, we confirm the existence of the topological phase in line with previous theoretical predictions. Our simulation results show that the transition between the confined topological phase and the deconfined paramagnetic phase is of first order, in contrast to the conventional Z 2 lattice gauge model in which the transition maps onto that of the standard Ising model and is continuous. We further generalize the model by replacing the transverse field on the gauge spins with a ferromagnetic X X interaction while keeping the local gauge symmetry intact. We find that the Z 2 topological phase remains stable, while the paramagnetic phase is replaced by a ferromagnetic phase. The topological-ferromagnetic quantum phase transition is also of first order. For both models, we discuss the low-energy spinon and vison excitations of the topological phase and their avoided level crossings associated with the first-order quantum phase transitions.

2-dimensional systems↗
DOE OSTI2023

Universal time-dependent Ginzburg-Landau theory

We study the hydrodynamics of superconductors within the framework of Schwinger-Keldysh effective field theory (EFT). We show that in the vicinity of the superconducting phase transition the most general leading-order EFT satisfying the local Kubo-Martin-Schwinger condition is described by a version of the time-dependent Ginzburg-Landau (TDGL) equations augmented with stochastic terms. This version of TDGL is applicable in the gapless regime independent of any microscopic details. Within this approach, it is possible to include systematically the effects of nonuniform temperature and heat conductivity, as well as explicit or spontaneous breaking of time reversal. Here, we also introduce a thermal version of the Josephson relation and use it to construct an exotic hydrodynamics describing a phase of matter where heat can flow without dissipation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Quantum simulation: From spin models to gauge-gravity correspondence

Quantum many-body systems with coherent and controllable interactions enable the realization of novel quantum materials, the quantum simulation of problems that cannot be simulated on classical computers, computational systems that are exponentially faster than existing classical algorithms, and the direct investigation of the conjectured duality between gravitational theories and quantum field theories. This project focusses on quantum phase transitions in strongly interacting many-body spin systems, and in particular on the dynamical evolution near the critical point and across the phase transition. The dynamics of a large quantum system containing more than 50 qubits is investigated in various critical regimes. In particular, the Kibble-Zurek transition has been characterized and critical exponents have been measured. Furthermore, quantum many-body scars have been observed and characterized for the first time. We are investigating the Kibble-Zurek mechanism in the quantum phase transition in one dimension from a disordered system to a system with ordering induced by Rydberg interactions between neighboring atoms. The Kibble-Zurek mechanism describes the formation of topological defects as a system evolves across a phase transitions, and is expected to apply to a large number of problems, including cosmology, where it should describe the structure of domain formation in the early universe.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2024

Two-step electronic response to magnetic ordering in a van der Waals ferromagnet

The two-dimensional material Cr 2 ⁢Ge 2 ⁢Te 6 is a member of the class of insulating van der Waals (vdW) magnets. Here, using high resolution angle-resolved photoemission spectroscopy in a detailed temperature dependence study, we identify a clear response of the electronic structure to a dimensional crossover in the form of two distinct temperature scales marking onsets of modifications in the electronic structure. Specifically, we observe Te 𝑝-orbital-dominated bands to undergo changes at the Curie transition temperature 𝑇 𝐶 while the Cr 𝑑-orbital-dominated bands begin evolving at a higher temperature scale. Combined with neutron scattering, density functional theory calculations, and Monte Carlo simulations, we find that the electronic system can be consistently understood to respond sequentially to the distinct temperatures at which in-plane and out-of-plane spin correlations exceed a characteristic length scale. Finally, our findings reveal the sensitivity of the orbital-selective electronic structure for probing the dynamical evolution of local moment correlations in vdW insulating magnets.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2020

Organic Components of Small Bodies in the Outer Solar System: Some Results of the New Horizons Mission

The close encounters of the Pluto–Charon system and the Kuiper Belt object Arrokoth (formerly 2014 MU 69 ) by NASA’s New Horizons spacecraft in 2015 and 2019, respectively, have given new perspectives on the most distant planetary bodies yet explored. These bodies are key indicators of the composition, chemistry, and dynamics of the outer regions of the Solar System’s nascent environment. Pluto and Charon reveal characteristics of the largest Kuiper Belt objects formed in the dynamically evolving solar nebula inward of ~30 AU, while the much smaller Arrokoth is a largely undisturbed relic of accretion at ~45 AU. The surfaces of Pluto and Charon are covered with volatile and refractory ices and organic components, and have been shaped by geological activity. On Pluto, N 2 , CO and CH 4 are exchanged between the atmosphere and surface as gaseous and condensed phases on diurnal, seasonal and longer timescales, while Charon’s surface is primarily inert H 2 O ice with an ammoniated component and a polar region colored with a macromolecular organic deposit. Arrokoth is revealed as a fused binary body in a relatively benign space environment where it originated and has remained for the age of the Solar System. Its surface is a mix of CH 3 OH ice, a red-orange pigment of presumed complex organic material, and possibly other undetected components.

Solar System↗
DOE OSTI2022

Efficient and universal characterization of atomic structures through a topological graph order parameter

Abstract A graph-based order parameter, based on the topology of the graph itself, is introduced for the characterization of atomistic structures. The order parameter is universal to any material/chemical system and is transferable to all structural geometries. Four sets of data are used to validate both the generalizability and accuracy of the algorithm: (1) liquid lithium configurations spanning up to 300 GPa, (2) condensed phases of carbon along with nanotubes and buckyballs at ambient and high temperature, (3) a diverse set of aluminum configurations including surfaces, compressed and expanded lattices, point defects, grain boundaries, liquids, nanoparticles, all at nonzero temperatures, and (4) eleven niobium oxide crystal phases generated with ab initio molecular dynamics. We compare our proposed method to existing, state-of-the-art methods for the cases of aluminum and niobium oxide. Our order parameter uniquely classifies every configuration and outperforms all studied existing methods, opening the door for its use in a multitude of complex application spaces that can require fine structure-level characterization of atomistic graphs.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Temperature and conductivity in shock compressed bridgmanite MgSiO 3 up to 2 TPa

The melting behavior and transport properties of MgSiO 3 at multi-megabar pressures remain poorly constrained despite their importance for high-pressure silicate physics. Here we report the first direct measurements of temperature and optical reflectivity in shock-compressed bridgmanite (MgSiO 3 ) using laser-driven decaying shock compression combined with velocimetry and optical pyrometry. Temperature and reflectivity data spanning approximately 4000–60 000 K were used to constrain the MgSiO 3 melting curve and to infer its electrical conductivity. We find that the MgSiO 3 melting curve becomes shallower than that of iron above 400 GPa, yielding lower melting temperatures in planetary mantles than predicted by several previous theoretical estimates. Across the solid-liquid transition, the inferred electrical conductivity increases significantly, reaching ∼2000 Ω cm −1 . These results provide experimental benchmarks for theoretical models of silicate melting and transport under extreme pressure-temperature conditions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Nonmonotonic crossover in electronic phase separated manganite superlattices driven by the superlattice period

Studying manganite superlattices [(LCMO) 2n / (PCMO) n ] t made of La 0.625 Ca 0.375 MnO 3 (LCMO) and Pr 0.625 Ca 0.375 MnO 3 (PCMO), we found an unexpected behavior varying the period n. At small n, the ensemble is a three-dimensional ferromagnetic metal due to interfacial charge transfer. At large n , the LCMO layers dominate transport. However, rather than a smooth interpolation between these limits a sharp transport and magnetic anomaly is found at an intermediate critical PCMO thickness n*. Magnetic force microscopy reveals that the phase-separation length scale also maximizes at n* where, unexpectedly, it becomes comparable to that of the (La 1-y Pr y ) 0.625 Ca 0.375 MnO 3 (LPCMO) alloy. Finally, we conjecture the phenomenon originates in a disorder-related length scale: Large charge-ordered clusters as in LPCMO can only nucleate when Pr-rich regions reach a critical size related to n*.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Valley-Coherent Quantum Anomalous Hall State in AB-Stacked MoTe 2 / W S e 2 Bilayers

Moiré materials provide fertile ground for the correlated and topological quantum phenomena. Among them, the quantum anomalous Hall (QAH) effect, in which the Hall resistance is quantized even under zero magnetic field, is a direct manifestation of the intrinsic topological properties of a material and an appealing attribute for low-power electronics applications. The QAH effect has been observed in both graphene and transition metal dichalcogenide (TMD) moiré materials. It is thought to arise from the interaction-driven valley polarization of the narrow moiré bands. Here, we show that the newly discovered QAH state in AB-stacked MoTe 2 / W S e 2 moiré bilayers is not valley polarized but valley coherent. The layer- and helicity-resolved optical spectroscopy measurement reveals that the QAH ground state possesses spontaneous spin (valley) polarization aligned (antialigned) in two TMD layers. In addition, saturation of the out-of-plane spin polarization in both layers occurs only under high magnetic fields, supporting a canted spin texture. Our results call for a new mechanism for the QAH effect and highlight the potential of TMD moiré materials with strong electronic correlations and spin-orbit interactions for exotic topological states. Published by the American Physical Society 2024

2-dimensional systems↗
NASA NTRS1987

Design and test of a mechanically pumped two-phase thermal control flight experiment

A flight experiment of a mechanically pumped two-phase ammonia thermal control system, incorporating a number of new component designs, has been assembled and tested in a 1-g environment. Additional microgravity tests are planned on the Space Shuttle when Shuttle flights are resumed. The primary purpose of this experiment is to evaluate the operation of a mechanically pumped two-phase ammonia system, with emphasis on determining the performance of an evaporative Two-Phase Mounting Plate. The experiment also evaluates the performance of other specially designed components, such as the two-phase reservoir for temperature control, condensing radiator/heat sink, spiral tube boiler, and pressure drop experiment. The 1-g tests have shown that start-up of the two-phase experiment is easily accomplished with only a partial fill of ammonia. The experiment maintained a constant mounting plate temperature without flow rate controls over a very wide range of heat loads, flow rates, inlet flow conditions and exit qualities. The tests also showed the successful operation of the mounting plate in the heat sharing condensing mode.

Grote, M. G.↗
NASA NTRS1994

Constraints on chondrule and CAI origins from vapor-liquid-solid experiments

It has been widely accepted that evaporation played an important role in the formation of chondritic constituents and elemental and isotopic fractionation in the solar nebula. Although many workers consider that evaporation is just the opposite of condensation, it is true only when the process is in equilibrium. When the process is not in equilibrium, e.g., local evaporation, where generated gas moves away from the residual solids, the fractionation path is quite different from the opposite of condensation of the gas with the solar system elemental abundances. The degree of elemental, particularly isotopic, fractionation is strongly dependent on the evaporation rate of the element when evaporation takes place from solid materials. The phase relations and the rate of evaporation of chondrite-forming minerals give constraints on partial pressure of the dust components, total pressure of the nebular gas, and heating rate of the materials.

Nagahara, H.↗
DOE OSTI2021

Gauging anomalous unitary operators

Boundary theories of static bulk topological phases of matter are obstructed in the sense that they cannot be realized on their own as isolated systems. The obstruction can be quantified/characterized by quantum anomalies, in particular when there is a global symmetry. Similarly, topological Floquet evolutions can realize obstructed unitary operators at their boundaries. In this paper, we discuss the characterization of such obstructions by using quantum anomalies. As a particular example, here we discuss time-reversal symmetric boundary unitary operators in one and two spatial dimensions, where the anomaly emerges as we gauge the so-called Kubo-Martin-Schwinger (KMS) symmetry. We also discuss mixed anomalies between particle number conserving U(1) symmetry and discrete symmetries, such as C and CP, for unitary operators in odd spatial dimensions that can be realized at the boundaries of topological Floquet systems in even spatial dimensions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1987

A flash spectrum of Cl I, C I, N I, and Ni II absorption in 31 Cygni: A direct observation of the reversing layer

In the process of surveying IUE observations of the zeta Aurigae binary system 31 Cygni for evidence of a shock, the presence of narrow low temperature lines Cl I, C I, N I, and Ni II has been discovered. These lines cannot be due to the local interstellar medium, since they appear only in one of the 16 high resolution, short wavelength observations made of this system. The phase of their appearance is theta = 0.017, approximately two months after egress of the blue dwarf component from eclipse behind the cool supergiant. Such lines might be produced by the shining of the hot dwarf companion's continuum through the edge of the supergiant's reversing layer or through a condensation in the supergiant atmosphere. If the former is the case, then the height of the reversing layer may be estimated from this observation. The radial velocities and equivalent widths of ten of these lines have been measured and the former is found to be -8.2 +/- 0.5 km/sec, precisely equal to the radial velocity of the system center of mass. This places a strict upper limit on the rotational velocity of the supergiant: V sub rot less than 2 km/s to better than 3 sigma.

Ahmad, Imad A.↗
DOE OSTI2021

Iterated projected position algorithm for constructing exponentially localized generalized Wannier functions for periodic and nonperiodic insulators in two dimensions and higher

Localized bases play an important role in understanding electronic structure. In periodic insulators, a natural choice of localized basis is given by the Wannier functions which depend on a choice of unitary transform known as a gauge transformation. Over the past few decades, there have been many works that have focused on optimizing the choice of the gauge so that the corresponding Wannier functions are maximally localized or reflect some symmetry of the underlying system. In this work, we consider fully nonperiodic materials where the usual Wannier functions are not well defined and gauge optimization is impractical. To tackle the problem of calculating exponentially localized generalized Wannier functions in both periodic and nonperiodic systems, we discuss the ‘iterated projected position (IPP)” algorithm. Here, the IPP algorithm is based on matrix diagonalization and therefore unlike optimization-based approaches, it does not require initialization and cannot get stuck at a local minimum. Furthermore, the IPP algorithm is guaranteed by a rigorous analysis to produce exponentially localized functions under certain mild assumptions. We numerically demonstrate that the IPP algorithm can be used to calculate exponentially localized bases for the Haldane model, the Kane-Mele model (in both Z 2 invariant even and Z 2 invariant odd phases), and the p x + ip y model on a quasicrystal lattice.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Nonperturbative study of bulk photovoltaic effect enhanced by an optically induced phase transition

Solid systems with strong correlations and interactions under light illumination have the potential for exhibiting interesting bulk photovoltaic behavior in the non-perturbative regime, which has remained largely unexplored in the past theoretical studies. We investigate the bulk photovoltaic response of a perovskite manganite with strongly coupled electron-spin-lattice dynamics, using real-time simulations performed with a tight-binding model. The transient changes in the band structure and the photoinduced phase transitions, emerging from spin and phonon dynamics, result in a nonlinear current versus intensity behavior beyond the perturbative limit. The current rises sharply across a photoinduced magnetic phase transition, which later saturates at higher light intensities due to excited phonon and spin modes. The predicted peak photoresponsivity is orders of magnitude higher than other known ferroelectric oxides such as BiFeO$_3$. We disentangle phonon-and spin-assisted components to the ballistic photocurrent, showing that they are comparable in magnitude. Our results illustrate a promising alternative way for controlling and optimizing the bulk photovoltaic response through the photoinduced phase transitions in strongly-correlated systems.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2024

Experimentation on Finned-Tube Microchannel Heat Exchanger Incorporating Phase Change Material and R-410A

Integrating latent heat thermal energy storage, particularly phase change materials (PCM), in building heating, ventilation, air conditioning, and refrigeration (HVAC&R) systems, offers substantial benefits for peak load shifting and energy efficiency. While numerous studies explore PCM-embedded heat exchangers (PCM-HX) using single-phase heat transfer fluids, there needs to be more investigation regarding PCM-HX utilizing two-phase refrigerant flow. This gap is even more pronounced for microchannel heat exchanger (MCHX) configurations. In this study, an MCHX-based PCM-HX was built and tested to analyze and evaluate the performance of a PCM-HX operating with a two-phase refrigerant as the working fluid. A commercially available MCHX condenser unit was embedded with 2.6 kg of RT35 PCM and tested using R-410A as the working fluid, using an in-house test loop to control the refrigerant inlet conditions precisely. Thin and minimally invasive T-type thermocouples traced the temperature evolution along MCHX channels and tube banks. Additional larger T-type thermocouple probes at the refrigerant inlet and outlet measured the average power of the PCM-HX during condensing tests, ranging from 0.7 kW to 1.6 kW based on mass flow rates varying from 3.5 g/s to 8 g/s. This experimental study on MCHX-based PCM-HX with a two-phase refrigerant has the potential to offer practical design guidelines for the direct integration of PCM-TES in HVAC&R systems without the use of a secondary loop, while caution is advised to avoid a substantial increase in the refrigerant charge amount.

42 ENGINEERING↗
DOE OSTI2023

Global quantum phase diagram and non-Abelian chiral spin liquid in a spin- 3 2 square-lattice antiferromagnet

Since strong quantum fluctuations are essential for the emergence of quantum spin liquids, there have been extensive exploration and identification of spin liquid candidates in spin-$\frac{1}{2}$ systems, while such activities are rare in higher spin systems. Here we report an example of non-Abelian chiral spin liquid emerging in a spin-$\frac{3}{2}$ Heisenberg model on a square lattice. By tuning Heisenberg exchange interaction and scalar chirality interaction, we map out a quantum phase diagram enclosing three conventional magnetic orders and a chiral spin liquid based on density-matrix renormalization group studies. The nature of the spin liquid is identified as a long-sought bosonic version of the Read-Rezayi state that supports non-Abelian Fibonacci anyonic statistics, identified by the ground state entanglement spectrum. Significantly, we establish that the non-Abelian chiral spin liquid emerges through the enlarged local degrees of freedom and enhanced quantum fluctuations near the classical phase boundaries of competing magnetic orders. Finally, our numerical discovery of an exotic quantum spin liquid in a spin-$\frac{3}{2}$ system suggests a route for discovering fractionalized quantum phases in frustrated higher spin magnetic compounds.

2-dimensional systems↗