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Results for “Methods in superconductivity”

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 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Sensitivity analysis of static resistance of slender beam under bending

The paper deals with statical and sensitivity analyses of resistance of simply supported I-beams under bending. The resistance was solved by geometrically nonlinear finite element method in the programme Ansys. The beams are modelled with initial geometrical imperfections following the first eigenmode of buckling. Imperfections were, together with geometrical characteristics of cross section, and material characteristics of steel, considered as random quantities. The method Latin Hypercube Sampling was applied to evaluate statistical and sensitivity resistance analyses.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Crystal Growth and Structural Characterization of a Thiocyanato-Bridged Copper(I/II) Mixed-Valence Coordination Polymer

A new mixed-valence coordination polymer [Cu{sub 3}(SCN){sub 4}(DMSO){sub 2}]{sub n} (SCN{sup –} = thiocyanato and DMSO = dimethyl sulfoxide) was prepared and characterized by single crystal X-ray diffraction method. The in situ formation of thiocyanate during the synthesis induces reduction of a part of Cu(II) to Cu(I). The three-dimensional structure of the binuclear thiocyanato bridged compound provided an example of pseudohalide materials containing two different environments for both copper centers.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Refining T c Prediction in Hydrides via Symbolic‐Regression‐Enhanced Electron‐Localization‐Function‐Based Descriptors

Hydrogen‐based materials are able to possess extremely high superconducting critical temperatures, T c s , due to hydrogen's low atomic mass and strong electron–phonon interaction. Recently, a descriptor based on the Electron Localization Function (ELF) has enabled the rapid estimation of the T c of hydrogen‐containing compounds from electronic networking properties, but its applicability has been limited by the small size and homogeneity of the training dataset used. Herein, the model is re‐examined, compiling a publicly available combined dataset of 244 binary and ternary hydride superconductors. The analysis shows that though ELF‐based networking remains a valuable descriptor, its predictive power declines with increasing compositional complexity. However, by introducing the molecularity index, defined as the highest value of the ELF at which two hydrogen atoms connect, and applying symbolic regression, the accuracy of the predictions can be substantially enhanced. These results establish a more robust framework for assessing superconductivity in hydride materials, facilitating accelerated screening of novel candidates through integration with crystal structure prediction methods or high‐throughput searches.

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

Mitigating coherent loss in superconducting circuits using molecular self-assembled monolayers

In planar superconducting circuits, decoherence due to materials imperfections, especially two-level-system (TLS) defects at different interfaces, is a primary hurdle for advancing quantum computing and sensing applications. Traditional methods for mitigating TLS loss, such as etching oxide layers at metal and substrate interfaces, have proven to be inadequate due to the persistent challenge of oxide regrowth. In this work, we introduce a novel approach that employs molecular self-assembled monolayers (SAMs) to chemically bind at different interfaces of superconducting circuits. This technique is specifically tested here on coplanar waveguide (CPW) resonators, in which this method not only impedes oxide regrowth after surface etching but can also tailors the dielectric properties at different resonators interfaces. The deployment of SAMs results in a consistent improvement in the measured quality factors across multiple resonators, surpassing those with only oxide-etched resonators. The efficiency of our approach is supported by microwave measurements of multiple devices conducted at millikelvin temperatures and correlated with detailed X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) characterizations of SAM-passivated resonators. The compatibility of SAMs materials with the established fabrication techniques offers a promising route to improve the performance of superconducting quantum devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Structural, Spectroscopic, Antimicrobial Activity and DFT Studies on 4-Methyl-N-(4-methylphenylsulfonyl)-N-phenylbenzenesulfonamide

This study reports the structural characterization of a disulfonimide derivative, 4-methyl-N-(4-methylphenylsulfonyl)-N-phenylbenzenesulfonamide (MPBSA), using spectroscopic and quantum chemical methods. The molecule was characterized with FT-IR, {sup 1}H {sup 13}C NMR and UV-Vis spectroscopies. Quantum chemical calculations of molecular geometry, vibrational wavenumbers and gauge including atomic orbital (GIAO) {sup 1}H and {sup 13}C-NMR chemical shifts of the compound were carried out by using density functional method (DFT) at B3LYP/6−311++G(d,p) level of theory. Electronic absorption spectra of the compound have been computed using the time-dependent density functional theory (TD-DFT) method at the same level. A satisfactory consistency between the experimental and theoretical findings was obtained. The antimicrobial activity screening of the compound was performed on some bacteria and fungus species using microdilution method. The results showed that the title molecule have noteworthy antibacterial and antifungal activities.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Stationary quasi-breathers in monatomic FCC metals

The characteristics of quasi-breathers in monatomic fcc metals are investigated by the molecular dynamics method. The standard deviations of the frequencies of atoms constituting a breather from the fundamental frequency of oscillations are calculated. It is shown that the quasi-breather lifetime in the models under investigation depends on the initial excitation conditions as well as on the metal type.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Superconductivity in the Li-B-C system at 100 GPa

Layer Li-B-C compounds have been shown to have feasible superconductivity. Using the adaptive genetic algorithm, we predict the structures of the Li-B-C system at 100 GPa. Here we identify several low-enthalpy metallic phases with stoichiometries of Li B 2 C, Li B 3 C, Li 2 BC 2 , Li 3 B 2 C 3 , Li 3 BC, and Li 5 BC. Using a fast screening method of electron-phonon interaction, we find that Li B 3 C is a promising candidate for superconductivity. The consecutive calculations using the full Brillouin zone confirm the existence of the strong electron-phonon coupling (EPC) in this system. The anharmonic B-C phonon modes near the zone center provide the major contribution to the EPC. The EPC constant is 1.40, and the estimated critical temperature is 22 K. In this paper, we indicate that superconductivity can also happen without a layered structural motif in the Li-B-C system. We also demonstrate an effective strategy for crystal structure prediction of superconducting materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Numerical and experimental study of Lamb wave propagation in a two-dimensional acoustic black hole

The propagation of laser-generated Lamb waves in a two-dimensional acoustic black-hole structure was studied numerically and experimentally. The geometrical acoustic theory has been applied to calculate the beam trajectories in the region of the acoustic black hole. The finite element method was also used to study the time evolution of propagating waves. An optical system based on the laser-Doppler vibration method was assembled. The effect of the focusing wave and the reduction in wave speed of the acoustic black hole has been validated.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

A nanoemitter based on a superconducting material

The coherence of an electron beam is crucial for the performance of electron microscopy, coherent diffractive imaging, holography, and many other advanced instrumentation methods that rely on the phase coherence of electron waves. Here we present a reliable method for preparing a niobium nanoemitter, which is thermally and chemically stable. The tip apex is a (100) facet with a lateral dimension of ∼1 nm, surrounded by four (310) facets. Adsorption of one monolayer of noble gas, particularly Xe, onto the nanoemitter greatly enhances the emission current and current stability. This electron source will probably possess both spatial and temporal coherence if the emitter is cooled below the superconducting temperature.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

First Results of ELM Triggering With a Multichamber Lithium Granule Injector Into EAST Discharges

A critical challenge facing the basic long-pulse H-mode for ITER is to control edge-localized modes (ELMs). A new method using a multichamber lithium (Li) granule injector (LGI) for ELM triggering experiments has been developed in Experimental Advanced Superconducting Tokamak (EAST). First experimental results of the control of ELMs are obtained in EAST with a tungsten divertor. It is found that the injector has good capacities, i.e., allowing good flexibilities in granule size selection, injection rate, and injection velocity. In conclusion, LGI has successfully triggered ELMs during the H-mode. These results indicate the LGI would be a promising method to control ELMs in long-pulse steady-state tokamaks.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Magnon interactions in the quantum paramagnetic phase of CoNb 2 O 6

In this work, we study effects of magnon interactions in the excitation spectrum of CoNb 2 O 6 in the quantum paramagnetic phase in transverse field, where the 1/S spin-wave theory exhibits unphysical divergences at the critical field. We propose a self-consistent Hartree-Fock approach that eliminates such unphysical singularities while preserving the integrity of the singular threshold phenomena of magnon decay and spectrum renormalization that are present in both theory and experiment. With the microscopic parameters adopted from previous studies, this method yields a close quantitative agreement with the available experimental data for CoNb 2 O 6 in the relevant regime. Furthermore, insights into the general structure of the spin-anisotropic model of CoNb 2 O 6 and related zigzag chain materials are also provided and a discussion of the effects of additional longitudinal field on the spectrum is given.

1-dimensional spin chains↗
DOE OSTI2018

Study of the Structural, Electronic, Magnetic, and Optical Properties of Mn{sub 2}ZrGa Full-Heusler Alloy: First-Principles Calculations

In this work, the structural, electronic, magnetic, and optical properties of Mn{sub 2}ZrGa full-Heusler alloy were investigated by using density functional theory (DFT) calculations. It is found that the spin-up states have a metallic character, but the spin-down bands have a pseudo-gap at the Fermi level. The total spin magnetic moment of Mn{sub 2}ZrGa (per formula unit) is 3.00 µ{sub B} at an equilibrium lattice parameter of 6.15 Å. The calculations show that Mn{sub 2}ZrGa is a ferrimagnetic with 81% spin polarization at equilibrium lattice parameter. The effect of lattice parameter distortion on the magnetic properties and spin polarization is also studied. It is found that the total magnetic moment preserves its value for a lattice parameter range of 5.96–6.30 Å. The decreasing of the lattice parameter leads to improvement of spin polarization. The real and imaginary parts of dielectric function and hence the optical properties including energy absorption spectrum, reflectivity, and optical conductivity are also calculated. The value of plasma frequency for spin-up and down electrons is located at 1.78 and 0.74 eV, respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Theoretical Investigation of Half-Metallic Ferromagnetism in Sodium-Based Fluoro-perovskite NaXF{sub 3} (X = V, Co)

We report on the structural, mechanical, magneto-electronic and thermodynamic properties of cubic sodium based fluoro-perovskite NaXF3 (X = V, Co) through density functional theory (DFT). The generalized gradient approximation of Perdew, Burke, and Ernzerh (GGA-PBE) and the Tran-Blaha modified Becke-Johnson potential (TB-mBJ) are used for modeling exchange-correlation effects. The calculated lattice parameters agree well with the experimental measurements. Elastic properties show that these compounds are mechanically stable. The results of spin-polarized band structure show a half metallic behavior of NaVF{sub 3} and NaCoF{sub 3}. The magnetic study shows that the nature of these compounds is ferromagnetic and the integer value of the total magnetic moment confirms the half metallicity for both materials. The thermodynamic characters are also investigated through quasi-harmonic approximation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Ab Initio Investigation on Electronic, Magnetic, Mechanical, and Thermodynamic Properties of AMO{sub 3} (A = Eu, M = Ga, In) Perovskites

The structural, electronic, magnetic, elastic, and thermodynamic properties of cubic AMO{sub 3} perovskites (A = Eu, M = Ga, In) have been successfully studied within density functional theory using full-potential linearized augmented plane wave (FP-LAPW). The structural study reveals that both the compounds are stable in ferromagnetic states. The GGA + U calculated spin-polarized electronic band and density of states present the half-metallic nature of both the compounds. The magnetic moments calculated with different approximations were found to be approximately 6 μ{sub B} for EuGaO{sub 3} and approximately 7 μ{sub B} for EuInO{sub 3}. From elastic calculation, the three independent elastic constants (C{sub 11}, C{sub 12}, C{sub 44}) have been acquired to yield the mechanical properties like Young modulus (Y ), shear modulus (G), Poisson ratio (ν), and anisotropic factor (A). The calculated values of B/G show that both the compounds are ductile in nature. The thermodynamic study was also accomplished by exploring the thermodynamic parameters like specific heat, heat capacity, thermal expansion, Grüneisen parameter, Debye temperature, etc. within the temperature range 0 to 900 K and pressure range 0 to 50 GPa.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Theoretical Investigations of Properties of New Half-Heusler Compounds NiFeZ (Z = Si, Ge)

The half-Heusler alloys NiFeZ (Z = Si, Ge) are investigated theoretically in the general framework of Density Functional Theory (DFT). We have calculated structural, mechanical, elastic, electronic, magnetic, and optical properties using WIEN2k simulation package. To incorporate the electronic exchange-correlation energy we have used the GGA+U approximation. Both the compounds are found structurally stable, however, elastic properties show that NiFeSi is ductile while NiFeGe is brittle. Electronically, the compounds are found to be half-metals with small band gaps in the spin-down channels whereas spin-up channels are conducting. The total magnetic moments for both the compounds are ≈ 2μ{sub B}. Optical properties including dielectric function, refractive index, extinction coefficient, reflectivity, conductivity, and absorption coefficient are also calculated and analyzed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Study of Effect of Bended Graphene on Its Magnetoresistance and Spin Filtration

Density functional theory (DFT) is used to investigate the spin-dependent quantum transport through bended graphene. Bending results in reduced bandgap in graphene and affects the spin transport by increasing current in parallel configuration (PC) resulting in an increase in magnetoresistance (MR). In antiparallel configuration (APC), bending limits the spin-down current, which results in higher magnetoresistance at all biases. In bended graphene, the magnetoresistance obtained is higher than the MR obtained in pristine and twisted graphene-based structure. High spin filtration for PC and APC is observed in the case of bended graphene as compared with pristine and twisted graphene. However, pristine graphene gives better spin filtration compared with twisted graphene at low voltages.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Origin of the Magnetism in Undoped and Mn-Doped In{sub 2}O{sub 3}: A First-Principles Study

The magnetism of undoped and Mn-doped In{sub 2}O{sub 3} has been investigated by employing density functional calculations. For undoped In{sub 2}O{sub 3}, a neutral In vacancy in In{sub 2}O{sub 3} leads to the formation of a net moment of 3 μ{sub B}, which originates from the strong spin polarization of 2p orbitals of O atoms. While, Mn-doped In{sub 2}O{sub 3} system shows robust ferromagnetism which can be attributed to the p-d hybridization between Mn and their neighboring O atoms. In addition, because two O atoms between the two Mn atoms are removed, the ground state of the system have a transformation from the ferromagnetic to the antiferromagnetic state, which further demonstrates that the ferromagnetism is mediated through the p-d interaction.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Enhanced Magnetoresistance in In-Plane Monolayer MoS{sub 2} with CrO{sub 2} Electrodes

Magnetoresistance of monolayer MoS{sub 2} is reported to increase when used in in-plane configuration with CrO{sub 2} half-metal ferromagnet (HMF) electrodes. Density functional theory (DFT)- and non-equilibrium Green’s function (NEGF)-based simulations show that high magnetoresistance (MR) values of ∼860% can be achieved in in-plane monolayer MoS{sub 2} with CrO{sub 2} electrodes, which is much higher than the MR value of ∼300% for nine-layer and the MR value of ∼70% for single-layer out-of-plane MoS{sub 2} reported in Dolui et al., Phys. Rev. B 90(R), 041401 (2014) past by other researchers. High spin-injection efficiency ∼100% is also obtained at high bias voltages. High MR and perfect spin filtration suggests the importance of this configuration in spintronics applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗