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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 OSTI2015

Exponentially decaying magnetic coupling in sputtered thin film FeNi/Cu/FeCo trilayers

Magnetic coupling in trilayer films of FeNi/Cu/FeCo deposited on Si/SiO{sub 2} substrates have been studied. While the thicknesses of the FeNi and FeCo layers were kept constant at 100 Å, the thickness of the Cu spacer was varied from 5 to 50 Å. Both hysteresis loop and ferromagnetic resonance results indicate that all films are ferromagnetically coupled. Micromagnetic simulations well reproduce the ferromagnetic resonance mode positions measured by experiments, enabling the extraction of the coupling constants. Films with a thin Cu spacer are found to be strongly coupled, with an effective coupling constant of 3 erg/cm{sup 2} for the sample with a 5 Å Cu spacer. The strong coupling strength is qualitatively understood within the framework of a combined effect of Ruderman-Kittel-Kasuya-Yosida and pinhole coupling, which is evidenced by transmission electron microscopy analysis. The magnetic coupling constant surprisingly decreases exponentially with increasing Cu spacer thickness, without showing an oscillatory thickness dependence. This is partially connected to the substantial interfacial roughness that washes away the oscillation. The results have implications on the design of multilayers for spintronic applications.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Thermodynamic properties of noninteracting quantum gases with spin-orbit coupling

In this brief report we study thermodynamic properties of noninteracting quantum gases with isotropic spin-orbit coupling. At high temperature, coefficients of virial expansion depend on both temperature T and spin-orbit coupling strength {kappa}. For strong coupling, virial expansion is applicable to the temperature region below the conventional degenerate temperature T{sub F}. At low temperature, specific heat is proportional to {radical}(T) in Bose gases and T in Fermi gases. Temperature dependence of the chemical potential of fermions shows a different behavior when the Fermi surface is above and below the Dirac point.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Strong Electronic Coupling of Molecular Sites to Graphitic Electrodes via Pyrazine Conjugation

Glassy carbon electrodes were functionalized with redox-active moieties by condensation of o-phenylenediamine derivatives with o-quinone sites native to graphitic carbon surfaces. Electrochemical and spectroscopic investigations establish that these graphite-conjugated catalysts (GCCs) exhibit strong electronic coupling to the electrode, leading to electron transfer (ET) behavior that diverges fundamentally from that of solution-phase or surface-tethered analogues. We find that (1) ET is not observed between the electrode and a redox-active GCC moiety regardless of applied potential. (2) ET is observed at GCCs only if the interfacial reaction is ion-coupled. (3) Even when ET is observed, the oxidation state of a transition metal GCC site remains unchanged. From these observations, we construct a mechanistic model for GCC sites in which ET behavior is identical to that of catalytically active metal surfaces rather than to that of molecules in solution. These results suggest that GCCs provide a versatile platform for bridging molecular and heterogeneous electrocatalysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Strong Electroosmotic Coupling Dominates Ion Conductance of 1.5 nm Diameter Carbon Nanotube Porins

Extreme confinement in nanometer sized channels can alter fluid and ion transport in significant ways, leading to significant water flow enhancement and unusual ion correlation effects. These effects are especially pronounced in carbon nanotube porins (CNTPs) that combine strong confinement in the inner lumen of carbon nanotubes with the high slip flow enhancement due to smooth hydrophobic pore walls. For this paper, we have studied ion transport and ion selectivity in 1.5 nm diameter CNTPs embedded in lipid membranes using single nanopore measurement setup. Our data show that CNTPs are weakly cation-selective at pH 7.5 and become non-selective at pH 3.0. Ion conductance of CNTPs exhibits an unusual 2/3 power law scaling with the ion concentration at both neutral and acidic pH values. Coupled Navier-Stokes and Poisson-Nernst-Planck (NS-PNP) simulations and atomistic Molecular Dynamics (MD) simulations reveal that this scaling originates from strong coupling between water and ion transport in these channels. These effects could result in development of a next generation of biomimetic membranes and carbon nanotube-based electroosmotic pumps.

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

Tip‐Enhanced Imaging and Control of Infrared Strong Light‐Matter Interaction

Optical antenna resonators enable control of light‐matter interactions on the nano‐scale via electron–photon hybrid states in strong coupling. Specifically, mid‐infrared (MIR) nano‐antennas coupled to saturable intersubband transitions in multi‐quantum‐well (MQW) semiconductor heterostructures allow for the coupling strength to be tuned through antenna resonance and field intensity. Here, in this study, tip‐enhanced nano‐scale variation of antenna‐MQW coupling across the antenna is demonstrated, with a spatially‐dependent coupling strength $g_{\textrm{aq}}$ varying from 73 (strong coupling) to 24 cm -1 (weak coupling). This behavior is modeled based on the spatially dependent local constructive and destructive interference between tip and antenna fields. Using a quantum‐mechanical density‐matrix model of the MQW system with its designed values of transition dipole moment, doping density, and population decay time, the picosecond IR pulse coupling to intersubband transitions and the associated tip induced strong‐field saturation effects are described. These results present a new regime of nonlinear IR light‐matter control based on the dynamic manipulation of quantum hybrid states on the nanoscale and in the infrared, with a perspective regarding extension to molecular vibrations.

Wang, Yueying↗
DOE OSTI2021

Dark matter detection, Standard Model parameters and Intermediate Scale Supersymmetry

The vanishing of the Higgs quartic coupling at a high energy scale may be explained by Intermediate Scale Supersymmetry, where supersymmetry breaks at (10 9 -10 12 ) GeV. The possible range of supersymmetry breaking scales can be narrowed down by precise measurements of the top quark mass and the strong coupling constant. On the other hand, nuclear recoil experiments can probe Higgsino or sneutrino dark matter up to a mass of 1012 GeV. We derive the correlation between the dark matter mass and precision measurements of standard model parameters, including supersymmetric threshold corrections. The dark matter mass is bounded from above as a function of the top quark mass and the strong coupling constant. The top quark mass and the strong coupling constant are bounded from above and below respectively for a given dark matter mass. We also discuss how the observed dark matter abundance can be explained by freeze-out or freeze-in during a matter-dominated era after inflation, with the inflaton condensate being dissipated by thermal effects.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Selective isomer emission via funneling of exciton polaritons

Polaritons in organic systems has shown the potential to modify chemical properties and to mediate long-range energy transfer between individual chromophores, among other capabilities. Here, we demonstrate that strong coupling and formation of organic exciton-polaritons can be used to selectively tune the isomer emission of organic molecules. By taking advantage of their delocalized and hybrid character, polaritons emerging in the strong coupling regime open a new relaxation pathway that allows for an efficient funneling of the excitation between the molecular isomers. We implement this by strong coupling to trans-DCS (E-4-dimethylamino-4'cyanostilbene)molecules, which present two isomers in different amounts when immersed in a polymer matrix. Thanks to this new relaxation pathway, the photoexcitation that is first shared by the common polaritonic mode is then selectively funneled to the excited states of one of the isomers, recognizing pure emission from the isomeric states that do not contribute to emission under normal conditions.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

Electronic structure and electron-phonon coupling in TiH$_2$

Calculations using first principles methods and strong coupling theory are carried out to understand the electronic structure and superconductivity in cubic and tetragonal TiH$_2$. A large electronic density of states at the Fermi level in the cubic phase arises from Ti-$t_{2g}$ states and leads to a structural instability against tetragonal distortion at low temperatures. However, constraining the in-plane lattice constants diminishes the energy gain associated with the tetragonal distortion, allowing the cubic phase to be stable at low temperatures. Furthermore, calculated phonon dispersions show decoupled acoustic and optic modes arising from Ti and H vibrations, respectively and frequencies of optic modes to be rather high. The cubic phase has a large electron-phonon coupling parameter $\lambda$ and critical temperature of several K. Contribution of the hydrogen sublattice to $\lambda$ is found to be small in this material, which we understand from strong coupling theory to be due to the small H-$s$ DOS at the Fermi level and high energy of hydrogen modes at the tetrahedral sites.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Superconducting phase diagram of H 3 S under high magnetic fields

The discovery of superconductivity at 260 K in hydrogen-rich compounds like LaH 10 re-invigorated the quest for room temperature superconductivity. Here, we report the temperature dependence of the upper critical fields μ 0 H c2 (T) of superconducting H 3 S under a record-high combination of applied pressures up to 160 GPa and fields up to 65 T. We find that H c2 (T) displays a linear dependence on temperature over an extended range as found in multigap or in strongly-coupled superconductors, thus deviating from conventional Werthamer, Helfand, and Hohenberg (WHH) formalism. The best fit of H c2 (T) to the WHH formalism yields negligible values for the Maki parameter α and the spin–orbit scattering constant λ SO . However, H c2 (T) is well-described by a model based on strong coupling superconductivity with a coupling constant λ ~ 2. We conclude that H 3 S behaves as a strong-coupled orbital-limited superconductor over the entire range of temperatures and fields used for our measurements.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2016

Coupling of Charged Particles Via Coulombic Interactions: Numerical Simulations and Resultant Kappa-Like Velocity Space Distribution Functions

A parametric study is performed using the electrostatic simulations of Randol and Christian (2014) in which the number density, n, and initial thermal speed, theta, are varied. The range of parameters covers an extremely broad plasma regime, all the way from the very weak coupling of space plasmas to the very strong coupling of solid plasmas. The first result is that simulations at the same Lambda(sub D), where Lambda(sub D) is the plasma coupling parameter, but at different combinations of n and theta, behave exactly the same. As a function of Lambda(sub D), the form of p(v), the velocity distribution function of v, the magnitude of v, the velocity vector, is studied. For intermediate to high D, heating is observed in p(v) that obeys conservation of energy, and a suprathermal tail is formed, with a spectral index that depends on Lambda(sub D). For strong coupling (Lambda(sub D) much > 1), the form of the tail is v5, consistent with the findings of Randol and Christian (2014). For weak coupling (Lambda(sub D much <1), no acceleration or heating occurs, as there is no free energy. The dependence on N, the number of particles in the simulation, is also explored. There is a subtle dependence in the index of the tail, such that v5 appears to be the N approaches infinity limit.

Randol, Brent M.↗
DOE OSTI2016

Ultralow-frequency collective compression mode and strong interlayer coupling in multilayer black phosphorus

The recent renaissance of black phosphorus (BP) as a two-dimensional (2D) layered material has generated tremendous interest, but its unique structural characters underlying many of its outstanding properties still need elucidation. Here we report Raman measurements that reveal an ultralow-frequency collective compression mode (CCM) in BP, which is unprecedented among similar 2D layered materials. This novel CCM indicates an unusually strong interlayer coupling, and this result is quantitatively supported by a phonon frequency analysis and first-principles calculations. Moreover, the CCM and another branch of low-frequency Raman modes shift sensitively with changing number of layers, allowing an accurate determination of the thickness up to tens of atomic layers, which is considerably higher than previously achieved by using high-frequency Raman modes. Lastly, these findings offer fundamental insights and practical tools for further exploration of BP as a highly promising new 2D semiconductor.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Discovery of a layered multiferroic compound Cu 1-x Mn 1+y SiTe 3 with strong magnetoelectric coupling

Multiferroic materials host both ferroelectricity and magnetism, offering potential for magnetic memory and spin transistor applications. Here, we report a multiferroic chalcogenide semiconductor Cu 1-x Mn 1+y SiTe 3 (0.04 ≤ x ≤ 0.26; 0.03 ≤ y ≤ 0.15), which crystallizes in a polar monoclinic structure (Pm space group). It exhibits a canted antiferromagnetic state below 35 kelvin, with magnetic hysteresis and remanent magnetization under 15 kelvin. We demonstrate multiferroicity and strong magnetoelectric coupling through magnetodielectric and magnetocurrent measurements. At 10 kelvin, the magnetically induced electric polarization reaches ~0.8 microcoulombs per square centimeter, comparable to the highest value in oxide multiferroics. We also observe possible room-temperature ferroelectricity. Given that multiferroicity is very rare among transition metal chalcogenides, our finding sets up a unique materials platform for designing multiferroic chalcogenides.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Self-assembly of nanocrystals into strongly electronically coupled all-inorganic supercrystals

Colloidal nanocrystals of metals, semiconductors, and other functional materials can self-assemble into long-range ordered crystalline and quasicrystalline phases, but insulating organic surface ligands prevent the development of collective electronic states in ordered nanocrystal assemblies. We reversibly self-assembled colloidal nanocrystals of gold, platinum, nickel, lead sulfide, and lead selenide with conductive inorganic ligands into supercrystals exhibiting optical and electronic properties consistent with strong electronic coupling between the constituent nanocrystals. The phase behavior of charge-stabilized nanocrystals can be rationalized and navigated with phase diagrams computed for particles interacting through short-range attractive potentials. By finely tuning interparticle interactions, the assembly was directed either through one-step nucleation or nonclassical two-step nucleation pathways. In the latter case, the nucleation was preceded by the formation of two metastable colloidal fluids.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Fermion masses through four-fermion condensates

Fermion masses can be generated through four-fermion condensates when symmetries prevent fermion bilinear condensates from forming. This less explored mechanism of fermion mass generation is responsible for making four reduced staggered lattice fermions massive at strong couplings in a lattice model with a local four-fermion coupling. The model has a massless fermion phase at weak couplings and a massive fermion phase at strong couplings. In particular there is no spontaneous symmetry breaking of any lattice symmetries in both these phases. Recently it was discovered that in three space-time dimensions there is a direct second order phase transition between the two phases. Here we study the same model in four space-time dimensions and find results consistent with the existence of a narrow intermediate phase with fermion bilinear condensates, that separates the two asymptotic phases by continuous phase transitions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Ultrafast 25-fs relaxation in highly excited states of methyl azide mediated by strong nonadiabatic coupling

Significance Highly excited states of neutral molecules behave qualitatively differently than the lower excited states that are commonly studied in photochemistry. Such states are involved in ionospheric and astrochemical phenomena, as well as in detonation processes. However, highly excited states are poorly understood due to experimental and theoretical challenges in probing their complex dynamics. Here, we apply vacuum-UV femtosecond laser sources and an imaging photoelectron–photoion coincidence spectrometer to directly probe the surprisingly fast 25-fs reaction pathway of the energetic molecule methyl azide. Combined with advanced calculations, we conclude that the electronic relaxation is driven by strong nonadiabatic coupling and that population transfer occurs along a seam well above the minimum energy conical intersection.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Universal molecular-confined synthesis of interconnected porous metal oxides-N-C frameworks for electrocatalytic water splitting

The rational synthesis of high performance electrocatalysts at low cost for water splitting (hydrogen and oxygen evolution reaction, HER and OER) is highly desirable but remains a key challenge. Herein, we report a versatile molecular-confining route to construct strongly coupled metal oxides-N-C frameworks with interconnected configuration. By simply chelating various transition metal ions with ethylenediaminetetraacetic acid disodium salt (EDTA) in agarose hydrogel and subsequent carbonization, the high specific surface area porous N-C frameworks with strongly coupled metal oxides (e.g., manganese, iron, cobalt, nickel and their mixed oxides) can be prepared as advanced nonprecious water splitting electrocatalysts. For instance, the resulting Co 3 O 4 -N-C frameworks with the high surface area of 153 m 2 g -1 , and the moderate nitrogen content of 1.23%, require an overpotential of 324 mV to afford a current density of 10 mA cm -2 in 0.1 M KOH for OER, superior to commercial RuO 2 catalysts. Density functional theory (DFT) calculations reveal that the strong coupling between N-C and Co 3 O 4 tunes the local electronic structure of Co for high-valence active sites and assures optimal adsorption energies of OER intermediates. Moreover, Co 2 P-N-C electrocatalysts derived from Co 3 O 4 -N-C also exhibit excellent HER performance under 1.0 M KOH with a low overpotential of 139 mV to reach 10 mA cm -2 , a small Tafel slope of 45 mV dec -1 and impressive stability, underscoring the versatility of our synthetic strategy.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Quantum Field Theory of Nematic Transitions in Spin-Orbit-Coupled Spin-1 Polar Bosons

We theoretically study an ultracold gas of spin-1 polar bosons in a one-dimensional continuum, which are subject to linear and quadratic Zeeman fields and a Raman induced spin orbit coupling. Concentrating on the regime in which the background fields can be treated perturbatively, we analytically solve the model in its low-energy sector; i.e., we characterize the relevant phases and the quantum phase transitions between them. Depending on the sign of the effective quadratic Zeeman field ε, two superfluid phases with distinct nematic order appear. In addition, we uncover a spin-disordered superfluid phase at strong coupling. We employ a combination of renormalization group calculations and duality transformations to access the nature of the phase transitions. At ε=0, a line of spin-charge separated pairs of Luttinger liquids divides the two nematic phases, and the transition to the spin-disordered state at strong coupling is of the Berezinskii-Kosterlitz-Thouless type. In contrast, at ε≠0, the quantum critical theory separating nematic and strong coupling spin-disordered phases contains a Luttinger liquid in the charge sector that is coupled to a Majorana fermion in the spin sector (i.e., the critical theory at finite ε maps to a quantum critical Ising model that is coupled to the charge Luttinger liquid). Because of an emergent Lorentz symmetry, both have the same logarithmically diverging velocity. We discuss the experimental signatures of our findings that are relevant to ongoing experiments in ultracold atomic gases of 23 Na.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2013

Circuit QED in a double quantum dot system

Strong coupling peculiar feature is demonstrated in a coupled qubit-resonator system consisting of a GaAs double quantum dot and a coplanar waveguide resonator. Qubit-resonator coupling strength (g and the decoherence rate Γ are directly derived from the experiment, assuring a strong coupling condition (g/Γ ≈ 2)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗