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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 1,387 records · Page 77

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DOE OSTI2021

Prediction of double-Weyl points in the iron-based superconductor CaKFe 4 As 4

Employing a combination of symmetry analysis, low-energy modeling, and ab initio simulations, we predict the presence of magnetic-field-induced Weyl points close to the Fermi level in CaKFe 4 As 4 . Depending on the relative strengths of the magnetic field and of the spin-orbit coupling, the Weyl fermions can carry a topological charge of ±1 or ±2, making CaKFe 4 As 4 a rare realization of a double-Weyl semimetal. Here, we further predict experimental manifestations of these Weyl points, both in bulk properties, such as the anomalous Hall effect, and in surface properties, such as the emergence of prominent Fermi arcs. Because CaKFe 4 As 4 displays unconventional fully gapped superconductivity below 30 K, our findings open a route to investigate the interplay between superconductivity and Weyl fermions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2022

Anomalous Hall effect at the Lifshitz transition in ZrTe 5

Zirconium pentatelluride ZrTe 5 is a topological semimetal. The presence of a temperature-induced Lifshitz transition, in which the Fermi level goes from the conduction band to the valence band with increasing temperature, provides unique opportunities to study the interplay between Fermi-surface topology, dynamics of Dirac fermions, and Berry curvature in one system. Here we present a combined experimental and theoretical study and show that a low-energy model can be used to understand the complicated Hall response and large anomalous Hall effect observed in ZrTe 5 over a wide range of temperature and magnetic field. We found that the anomalous Hall contribution dominates the Hall response in a narrow temperature window around the Lifshitz transition, away from which the orbital contribution dominates. Moreover, our results indicate that a topological phase transition coexists with the Lifshitz transition. To conclude, our model provides a unifying framework to understand the Hall effect in semimetals with large Zeeman splitting and nontrivial topology.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2023

Uniaxial stress study of spin and charge stripes in La1.875Ba0.125CuO4 by 139La NMR and 63Cu NQR

We study the response of spin and charge order in single crystals of La1.875Ba0.125CuO4 to uniaxial stress, through 139La nuclear magnetic resonance (NMR) and 63Cu nuclear quadrupole resonance (NQR), respectively. In unstressed La1.875Ba0.125CuO4, the low-temperature tetragonal structure onsets below TLTT = 57 K, while the charge order and the spin order transition temperatures are TCO = 54 K and TSO = 37 K, respectively. We find that uniaxial stress along the [110] lattice direction strongly suppresses TCO and TSO, but has little effect on TLTT. In other words, under stress along [110] a large splitting (≈ 21 K) opens between TCO and TLTT, showing that these transitions are not tightly linked. On the other hand, stress along [100] causes a slight suppression of TLTT but has essentially no effect on TCO and TSO. Magnetic field H along [110] stabilizes the spin order: the suppression of TSO under stress along [110] is slower under H ∥ [110] than H ∥ [001]. We develop a Landau free energy model and interpret our findings as an interplay of symmetry breaking terms driven by the orientation of spins.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2016

Tritium calibration of the LUX dark matter experiment

Here, we present measurements of the electron-recoil (ER) response of the LUX dark matter detector based upon 170,000 highly pure and spatially uniform tritium decays. We reconstruct the tritium energy spectrum using the combined energy model and find good agreement with expectations. We report the average charge and light yields of ER events in liquid xenon at 180 and 105 V/cm and compare the results to the NEST model. We also measure the mean charge recombination fraction and its fluctuations, and we investigate the location and width of the LUX ER band. These results provide input to a reanalysis of the LUX run 3 weakly interacting massive particle search.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Electrodynamics on Fermi Cyclides in Nodal Line Semimetals

We study the frequency-dependent conductivity of nodal line semimetals (NLSMs), focusing on the effects of carrier density and energy dispersion on the nodal line. Here, we find that the low-frequency conductivity has a rich spectral structure which can be understood using scaling rules derived from the geometry of their Dupin cyclide Fermi surfaces. We identify different frequency regimes, find scaling rules for the optical conductivity in each, and demonstrate them with numerical calculations of the inter- and intraband contributions to the optical conductivity using a low-energy model for a generic NLSM.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2019

Nonreciprocal Directional Dichroism Induced by the Quantum Metric Dipole

We identify the quantum metric dipole as the geometric origin of the nonreciprocal directional dichroism which describes the change in the refractive index upon reversing the light propagation direction. Specifically, we find that the static limit of the nonreciprocal directional dichroism corresponds to a quadrupolar transport current from the quantum metric dipole, in response to a quadrupolar electric field. Moreover, at a finite frequency, we demonstrate that the steepest slope of the averaged quantum metric dipole gives rise to a peak in the differential refractive index between counterpropagating lights. Lastly, we illustrate both features in a low-energy model.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2020

Flat Bands and Chiral Optical Response of Moiré Insulators

Here, we present a low-energy model describing the reconstruction of the electronic spectrum in twisted bilayers of honeycomb crystals with broken sublattice symmetry. The resulting moiré patterns are classified into two families with different symmetry. In both cases, flat bands appear at relatively large angles without any magic-angle condition. Transitions between them give rise to sharp resonances in the optical absorption spectrum at frequencies well below the gap of the monolayer. Owing to their chiral symmetry, twisted bilayers display circular dichroism, that is, different absorption of left and right circularly polarized light. This optical activity is a nonlocal property determined by the stacking. In hexagonal boron nitride, sensitivity to the stacking leads to strikingly different circular dichroism in the two types of moirés. Our calculations exemplify how subtle properties of the electronic wave functions, encoded in current correlations between the layers, control physical observables of moiré materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2016

Phantom of the Hartle–Hawking instanton: Connecting inflation with dark energy

If the Hartle–Hawking wave function is the correct boundary condition of our universe, the history of our universe will be well approximated by an instanton. Although this instanton should be classicalized at infinity, as long as we are observing a process of each history, we may detect a non-classicalized part of field combinations. When we apply it to a dark energy model, this non-classicalized part of fields can be well embedded to a quintessence and a phantom model, i.e., a quintom model. Because of the property of complexified instantons, the phantomness will be naturally free from a big rip singularity. This phantomness does not cause perturbative instabilities, as it is an effect emergent from the entire wave function. Lastly, our work may thus provide a theoretical basis for the quintom models, whose equation of state can cross the cosmological constant boundary phenomenologically.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2018

Interacting dark energy: possible explanation for 21-cm absorption at cosmic dawn

In this paper, a recent observation points to an excess in the expected 21-cm brightness temperature from cosmic dawn. In this paper, we present an alternative explanation of this phenomenon, an interaction in the dark sector. Interacting dark energy models have been extensively studied recently and there is a whole variety of such in the literature. Here we particularize to a specific model in order to make explicit the effect of an interaction.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2019

Dark energy induced anisotropy in cosmic expansion

In order to understand the nature of the accelerating expansion of the late-time universe, it is important to experimentally determine whether dark energy is a cosmological constant or dynamical in nature. If dark energy already exists prior to inflation, which is a reasonable assumption, then one expects that a dynamical dark energy would leave some footprint in the anisotropy of the late-time accelerated expansion. To demonstrate the viability of this notion, we invoke the quintessence field with the exponential potential as one of the simplest dynamical dark energy models allowed by observations. We investigate the effects of its quantum fluctuations (the physical origin of the perturbation being isocurvature) generated during inflation and having fully positive correlation with the primordial curvature perturbations, and estimate the anisotropy of the cosmic expansion so induced. We show that the primordial amplitude of quantum fluctuations of quintessence field δΦ P can be related to the tensor-to-scalar ratio r, and we calculate the perturbed luminosity distance to first order and the associated luminosity distance power spectrum, which is an estimator of anisotropy of late-time accelerated expansion. We find that the gravitational potential at large scales and late times is less decayed in QCDM compared to that in ΛCDM so that the smaller the redshift and multipole, the more relative deficit of power in QCDM. In conclusion, our results of luminosity distance power spectrum also show the similar conclusions of suppression as that of the previous investigation regarding the effect of quantum fluctuations of quintessence field on the CMB temperature anisotropies.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2018

NREL/OpenStudio

OpenStudio is a cross-platform collection of software tools to support whole building energy modeling using EnergyPlus and advanced daylight analysis using Radiance. This disclosure includes two OpenStudio measures: (1) data center prototype models, and (2) occupant schedule generator. The data center models cover two sizes (small computer server rooms, stand-alone large data centers) and two IT load densities (average and high).

Li, Han↗

DOE OSTI2016

OpenStudio® Server [SWR-07-40]

OpenStudio® Server is a web application and distributed computing tool, which is the backbone of the OpenStudio Analysis Framework (OSAF). It is intended to make parametric analysis of building energy models accessible to architects, engineers, and designers via the OpenStudio PAT GUI or the OpenStudio Analysis Gem. OpenStudio Server analyses are defined by PAT projects or OSA's. Each analysis may include many OpenStudio simulations, as determined by project configuration.

Long, Nicholas↗

DOE OSTI2019

Ladybug Tools IN2 Measures

Ladybug Tools IN2 Measures is a collection of OpenStudio® measures, file formats, scripts, and related tools for integrating Ladybug Tools with energy modeling via OpenStudio.

Macumber, Daniel↗

DOE OSTI2019

AERCalc v1.2.10

AERCalc is a software tool for evaluating the energy performance of window attachments (e.g., shading systems, attached window panels, etc.). All the annual energy modeling is performed by the EnergyPlus OS engine. The program incorporates a user-friendly GUI.

Mitchell, Robin↗

DOE OSTI2019

skyline

skyline is a header-only C++ library for the direct solution of linear algebraic equations that are stored in skyline format. It is intended for medium-sized sparse problems with moderate bandwidth. This solution approach has historically been used for pressure network solvers and in some finite element codes. It was developed to replace legacy solver code included in the EnergyPlus building energy modeling software package, but is not limited to use by EnergyPlus.

DeGraw, Jason↗

DOE OSTI2017

ACME Priority Metrics (A-PRIME)

A-PRIME, is a collection of scripts designed to provide Accelerated Climate Model for Energy (ACME) model developers and analysts with a variety of analysis of the model needed to determine if the model is producing the desired results, depending on the goals of the simulation. The software is csh scripts based at the top level to enable scientist to provide the input parameters. Within the scripts, the csh scripts calls code to perform the postprocessing of the raw data analysis and create plots for visual assessment.

Evans, KatherineJ.↗

DOE OSTI2021

Charging-management And Infrastructure-planning (cmip) Model

CMIP model explores various charging infrastructure network designs to serve a free-floating car-sharing fleet and determine the charging downtime experienced by the fleet for each design. Development of the CMIP model had two major steps: (1) describing modeling assumptions and (2) developing an integer program (IP) that jointly optimizes decisions about locations to install DC fast chargers and EV-to-charger assignments. The CMIP model integrates an EV charging model, EV energy consumption model, and heterogeneous, real-world vehicle use data with an integer programming optimization model to identify optimal location of new charging stations and calculate vehicle downtime for charging. The CMIP model can be applied to understand: (a) the reduction of EV fleet downtime if an additional fast-charging station is added to the current infrastructure and (b) to what extent total vehicle downtime would be sensitive to additional charging infrastructure.

Roni, MohammadS↗

DOE OSTI2023

EMF Biomass Data Interpreter [SWR-23-06]

EMF Biomass Data Interpreter was developed for the transportation team of the Energy Modeling Forum (EMF) 37: Deep Decarbonization and High Electrification Scenarios for North America project. It parses results from different modeling groups to show how biomass might be employed under electrification.

Wachs, Elizabeth↗