Search NASA⌕ Search

SEARCH · Search NASA

Results for “ELECTRON-ELECTRON INTERACTIONS”

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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Quantum Oscillations at Integer and Fractional Landau Level Indices in Single-Crystalline ZrTe 5

A three-dimensional (3D) Dirac semimetal (DS) is an analogue of graphene, but with linear energy dispersion in all (three) momentum directions. 3D DSs have been a fertile playground in discovering novel quantum particles, for example Weyl fermions, in solid state systems. Many 3D DSs were theoretically predicted and experimentally confirmed. Here, we report here the results in exfoliated ZrTe 5 thin flakes from the studies of aberration-corrected scanning transmission electron microscopy and low temperature magneto-transport measurements. We observed several unique results. First, a π Berry phase was obtained from the Landau fan diagram of the Shubnikov-de Haas oscillations in the longitudinal conductivity σ xx . Second, the longitudinal resistivity ρ xx shows a linear magnetic field dependence in the quantum limit regime. Most surprisingly, quantum oscillations were also observed at fractional Landau level indices N = 5/3 and 7/5, demonstrating strong electron-electron interaction effects in ZrTe 5 .

36 MATERIALS SCIENCE↗
DOE OSTI2011

E6 Gamma Decay

Rare electric hexacontatetrapole (E6) transitions are studied in the full (f{sub 7/2},f{sub 5/2},p{sub 3/2},p{sub 1/2}) shell-model basis. Comparison of theory to the results from the gamma decay in {sup 53}Fe and from inelastic electron scattering on {sup 52}Cr provides unique and interesting tests of the valence wavefunctions, the models used for energy density functionals and into the origin of effective charge.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Radiative Double Electron Capture Observed During O{sup 8+}+C Collisions At 38 Mev

Radiative double electron capture (RDEC) is a one-step process during which two free (or quasifree) target electrons are captured into bound states of the projectile, e.g., into an empty K-shell, and the energy excess is released as a single photon. This process can be considered as a time inverse of double photoionization. As photon interacts with one electron only, RDEC is due to electron-electron interaction. Moreover, RDEC is investigated during bare ion-atom collisions and, unlike double photoionization, it does not have background from spectator electrons. Thus, RDEC may be the simplest, clean tool for exploration of the electron-electron interaction in the presence of electromagnetic fields generated during ion-atom collisions. Recently, an experiment dedicated to the RDEC process with 38 MeV O{sup 8+} ions colliding with a carbon foil was conducted at Western Michigan University using the tandem Van de Graaff accelerator. This experiment confirmed that the observation of such process is possible and allowed for estimation of the RDEC cross section of 3.2(1.9) b, which is significantly greater than the theoretically predicted value of 0.15 b.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2011

Experimental Results in DIS, SIDIS and DES from Jefferson Lab

Jefferson Lab's electron accelerator in its present incarnation, with a maximum beam energy slightly above 6 GeV, has already enabled a large number of experiments expanding our knowledge of nucleon and nuclear structure (especially in Deep Inelastic Scattering--DIS--at moderately high x, and in the resonance region). Several pioneering experiments have yielded first results on Deeply Virtual Compton Scattering (DVCS) and other Deep Exclusive Processes (DES), and the exploration of the rich landscape of transverse momentum-dependent (TMD) structure functions using Semi-Inclusive electron scattering (SIDIS) has begun. With the upgrade of CEBAF to 12 GeV now underway, a significantly larger kinematic space will become available. The 12 GeV program taking shape will complete a detailed mapping of inclusive, TMD and generalized distribution functions for quarks, antiquarks and gluons in the valence region and beyond.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

The identification of a solvated electron pair in the gaseous clusters of Na{sup -}(H{sub 2}O){sub n} and Li{sup -}(H{sub 2}O){sub n}

By first principles calculations, we explore the possibility that Na{sup -}(H{sub 2}O){sub n} and Li{sup -}(H{sub 2}O){sub n} clusters, which have been measured previously by photoelectron experiments, could serve as gas-phase molecular models for the solvation of two electrons. Such models would capture the electron-electron interaction in a solution environment, which is missed in the well-known anionic water clusters (H{sub 2}O){sub n}{sup -}. Our results show that by n= 10, the two loosely bound s electrons in Li{sup -}(H{sub 2}O){sub n} are indeed detached from lithium, and they could exist in either the singlet (spin-paring) or the triplet (spin-coupling) state. In contrast, the two electrons would prefer to stay on the sodium atom in Na{sup -}(H{sub 2}O){sub n} and on the surface of the cluster. The formation of a solvated electron pair and the variation in solvation structures make these two cluster series interesting subjects for further experimental investigation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Self-Induced Oscillation for Electron-Hole Pair Confined in Quantum Dot

We study the time-dependent (TD) phenomena of the electron-hole or electron-electron pair confined in the square quantum dot (SQD) system by computationally solving TD Schroedinger equation under the unrestricted Hartree-Fock (UHF) approach. A typical vacillation is found both in the electron and hole when the charged pair is strongly confined in the SQD while the charged particles have initially the same orbital symmetry. The FFT analysis elucidates that the transition matrix element due to the coulomb interaction involves the eigen frequency {omega} being equal to the excitation energy when the resonative vacillation appears. Thus, Coulomb potential has a potential to cause the self-induced ''Rabi'' oscillation when the charged-particle pair is confined only in the QD.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

Femtosecond laser interactions with semiconductor and dielectric materials

Electronic excitation-relaxation processes induced by ultra-short laser pulses are studied numerically for semiconductors and dielectric materials (Si, quartz). A detailed kinetic approach is used in the calculations accounting for electron-photon-phonon, electron-phonon and electron-electron scatterings. In addition, both laser field ionization ranging from multi-photon to tunneling one, and electron impact (avalanche) ionization processes are included in the model. Based on the performed calculations we study the relaxation time as a function of laser parameters. It is shown that this time depends on the density of the created free carriers, which in turn is a nonlinear function of laser intensity. In addition, a simple damage criterion is proposed based on the mean electron energy density rather than on critical free electron density. This criterion gives a reasonable agreement with the available experimental data practically without adjustable parameters. Furthermore, the performed modeling provides energy absorbed in the target, conditions for damage of dielectric materials, as well as conditions for surface plasmon excitation and for periodic surface structure formation on the surface of semiconductor materials.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Layer-by-layer shuttered molecular-beam epitaxial growth of superconducting Sr{sub 1-x}La{sub x}CuO{sub 2} thin films

Superconducting Sr{sub 1-x}La{sub x}CuO{sub 2} thin films have been grown on GdScO{sub 3} substrates by reflection high-energy electron diffraction calibrated layer-by-layer molecular-beam epitaxy. X-ray diffraction analysis has confirmed the infinite layer structure after an in situ vacuum annealing step. In situ photoemission spectroscopy indicates that the vacuum annealing step employed immediately after film growth to achieve superconducting films results in oxygen loss from the films. The superconducting critical temperature depends on the La content x, with the highest value obtained for x{approx}0.10. Resistivity as a function of temperature {rho}(T) curves of optimally doped samples show a T{sup 2} temperature dependence characteristic of a scattering process where electron-electron interactions dominate.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Role of electron-electron interference in ultrafast time-resolved imaging of electronic wavepackets

Ultrafast time-resolved x-ray scattering is an emerging approach to image the dynamical evolution of the electronic charge distribution during complex chemical and biological processes in real-space and real-time. Recently, the differences between semiclassical and quantum-electrodynamical (QED) theory of light-matter interaction for scattering of ultrashort x-ray pulses from the electronic wavepacket were formally demonstrated and visually illustrated by scattering patterns calculated for an electronic wavepacket in atomic hydrogen [G. Dixit, O. Vendrell, and R. Santra, Proc. Natl. Acad. Sci. U.S.A. 109, 11636 (2012)]. In this work, we present a detailed analysis of time-resolved x-ray scattering from a sample containing a mixture of non-stationary and stationary electrons within both the theories. In a many-electron system, the role of scattering interference between a non-stationary and several stationary electrons to the total scattering signal is investigated. In general, QED and semiclassical theory provide different results for the contribution from the scattering interference, which depends on the energy resolution of the detector and the x-ray pulse duration. The present findings are demonstrated by means of a numerical example of x-ray time-resolved imaging for an electronic wavepacket in helium. It is shown that the time-dependent scattering interference vanishes within semiclassical theory and the corresponding patterns are dominated by the scattering contribution from the time-independent interference, whereas the time-dependent scattering interference contribution do not vanish in the QED theory and the patterns are dominated by the scattering contribution from the non-stationary electron scattering.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Electron correlation dynamics in atoms and molecules

In this paper, we present quantum dynamical calculations on electron correlation dynamics in atoms and molecules using explicitly time-dependent ab initio configuration interaction theory. The goals are (i) to show that in which cases it is possible to switch off the electronic correlation by ultrashort laser pulses, and (ii) to understand the temporal evolution and the time scale on which it reappears. We characterize the appearance of correlation through electron-electron scattering when starting from an uncorrelated state, and we identify pathways for the preparation of a Hartree-Fock state from the correlated, true ground state. Exemplary results for noble gases, alkaline earth elements, and selected molecules are provided. For Mg we show that the uncorrelated state can be prepared using a shaped ultrashort laser pulse.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2013

Two-dimensional weak anti-localization in Bi{sub 2}Te{sub 3} thin film grown on Si(111)-(7 Multiplication-Sign 7) surface by molecular beam epitaxy

We report on low temperature transport studies of Bi{sub 2}Te{sub 3} topological insulator thin films grown on Si(111)-(7 Multiplication-Sign 7) surface by molecular beam epitaxy. A sharp increase in the magnetoresistance with magnetic field at low temperature indicates the existence of weak anti-localization. The measured weak anti-localization effect agrees well with the Hikami-Larkin-Nagaoka model, and the extracted phase coherence length shows a power-law dependence with temperature indicating the existence of a two-dimensional system. An insulating ground state has also been observed at low temperature showing a logarithmic divergence of the resistance that appears to be the influence of electron-electron interaction in a two-dimensional system.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Impurity effects on polaron-exciton formation in conjugated polymers

Combining the one-dimensional tight-binding Su-Schrieffer-Heeger model and the extended Hubbard model, the collision of two oppositely charged polarons is investigated under the influence of impurity effects using a non-adiabatic evolution method. Results show that electron-electron interactions have direct influence on the charge distribution coupled to the polaron-exciton lattice defect. Additionally, the presence of an impurity in the collisional process reduces the critical electric field for the polaron-exciton formation. In the small electric field regime, the impurity effects open three channels and are of fundamental importance to favor the polaron-exciton creation. The results indicate that the scattering between polarons in the presence of impurities can throw a new light on the description of electroluminescence in conjugated polymer systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Precision electroweak studies using parity violation in electron scattering

The nature of new neutral-current interactions can be revealed at the low-energy precision frontier, where studies of parity-violation in electron scattering will complement the energy-frontier studies at the LHC. Measurements of the parity-violating observable A{sub PV} - the cross-section asymmetry in the scattering of longitudinally polarized electrons from an unpolarized target - are sensitive to possible contact interactions from new physics at multi-TeV mass scales. The 12 GeV upgrade at JLab and a new, high-intensity beam at Mainz offer opportunities for significant improvements in measurements of electron-electron and electron-quark parity-violating interactions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

Universal conductance fluctuations in electrolyte-gated SrTiO{sub 3} nanostructures

We report low-temperature magnetoconductance measurements of a patterned two-dimensional electron system at the surface of strontium titanate, gated by an ionic liquid electrolyte. We observe universal conductance fluctuations, a signature of phase-coherent transport in mesoscopic devices. From the universal conductance fluctuations, we extract an electron dephasing rate linear in temperature, characteristic of electron-electron interaction in a disordered conductor. The dephasing rate has a temperature-independent offset, which could possibly be explained by the presence of unscreened local magnetic moments in the sample.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2013

Measurements of aperture and beam lifetime using movable beam scrapers in Indus-2 electron storage ring

In this paper, the measurements of vertical and horizontal aperture which are available for stable beam motion in Indus-2 at beam energy 2.5 GeV using movable beam scrapers are presented. These beam scrapers are installed in one of the long straight sections in the ring. With the movement of beam scrapers towards the beam centre, the beam lifetime is measured. The beam lifetime data obtained from the movement of vertical and horizontal beam scrapers are analyzed. The contribution of beam loss due to beam-gas scattering (vacuum lifetime) and electron-electron scattering within a beam bunch (Touschek lifetime) is separated from the measured beam lifetime at different positions of the beam scrapers. Vertical and horizontal beam sizes at scrapers location are estimated from the scraper movement towards the beam centre in quantum lifetime limit and their values closely agree with measured value obtained using X-ray diagnostic beamline.

43 PARTICLE ACCELERATORS↗
DOE OSTI2013

Magnetic edge states in Aharonov-Bohm graphene quantum rings

The effect of electron-electron interaction on the electronic structure of Aharonov-Bohm (AB) graphene quantum rings (GQRs) is explored theoretically using the single-band tight-binding Hamiltonian and the mean-field Hubbard model. The electronic states and magnetic properties of hexagonal, triangular, and circular GQRs with different sizes and zigzag edge terminations are studied. The results show that, although the AB oscillations in the all types of nanoring are affected by the interaction, the spin splitting in the AB oscillations strongly depends on the geometry and the size of graphene nanorings. We found that the total spin of hexagonal and circular rings is zero and therefore, no spin splitting can be observed in the AB oscillations. However, the non-zero magnetization of the triangular rings breaks the degeneracy between spin-up and spin-down electrons, which produces spin-polarized AB oscillations.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Interacting spins and holes in zigzag edge nanographene

We have investigated charge and spin gap properties of zigzag edge graphene nanoribbons (ZGNRs) modeled within Hubbard Hamiltonian with onsite electron-electron interaction using semi-empirical many-body configuration interaction (CI) method. The charge gap behavior resembles the mean-field results, showing minima near Dirac point. We have observed unprecedented gap-less spin excitations over the flat band region. Moreover, doping the ZGNRs with holes reduces both the charge and spin gaps, inducing metallic and magnetic behavior, which can be exploited to fabricate spintronic devices.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Microwave studies of weak localization and antilocalization in epitaxial graphene

A microwave detection method was applied to study weak localization and antilocalization in epitaxial graphene sheets grown on both polarities of SiC substrates. Both coherence and scattering length values were obtained. The scattering lengths were found to be smaller for graphene grown on C-face of SiC. The decoherence rate was found to depend linearly on temperature, showing the electron-electron scattering mechanism.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗