Electron-Impact Double Ionization of the H2 Molecule
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Pindzola, Michael S↗
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Numerical simulation of the hot-tail runaway electron production mechanism using CQL3D and comparison with Smith–Verwichte analytical model
Abstract The hot-tail mechanism of runaway electron (RE) production (Harvey et al 2000 Phys. Plasmas 7 4590) is the primary source of RE in the case of rapidly cooling tokamak plasma. Quantifying this mechanism is very important as it can provide most of the post-thermal-quench (TQ) current, or a seed current for the secondary source of RE through the avalanche mechanism. An analytic model which omits pitch-angle scattering is often used in literature for estimating the hot-tail RE density (Smith and Verwichte 2008 Phys. Plasmas 15 072502). In the present study, we use the CQL3D bounce-averaged Fokker–Planck code (Harvey and McCoy 1992 Proc. IAEA Technical Committee Meeting on Advances in Simulation and Modeling of Thermonuclear Plasmas p 527) to test the limits of validity of the model. In particular, we examine the cases of Z = 1 and Z = 18 ions, for sets of different initial temperature, density, electric field and the characteristic time of temperature decay. We show that for Z = 1 plasma, the ratio of RE density computed by CQL3D to that estimated from the model is within 0.6–6.0 in studied cases. For the Z = 18 case, this factor is systematically a much smaller number, typically 0.02–0.6. We suggest a simple correction to the model that narrows down the range of this ratio to 0.3–3.8 in all of the cases, including Z = 1 and Z = 18 plasmas.
Physics↗
Search for excited electrons and muons in root s=8 TeV proton-proton collisions with the ATLAS detector
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72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Electronic Structure, Phonon Dynamical Properties, and CO 2 Capture Capability of Na 2 - x M x Zr O 3 ( M = Li ,K): Density-Functional Calculations and Experimental Validations
The electronic structural and phonon properties of Na 2-α M α ZrO 3 (M ¼ Li,K, α = ¼ 0.0,0.5,1.0,1.5,2.0) are investigated by first-principles density-functional theory and phonon dynamics. The thermodynamic properties of CO 2 absorption and desorption in these materials are also analyzed. With increasing doping level α, the binding energies of Na 2-α Li α ZrO 3 are increased while the binding energies of Na 2-α K α ZrO 3 are decreased to destabilize the structures. The calculated band structures and density of states also show that, at the same doping level, the doping sites play a significant role in the electronic properties. The phonon dispersion results show that few soft modes are found in several doped configurations, which indicates that these structures are less stable than other configurations with different doping levels. From the calculated relationships among the chemical-potential change, the CO 2 pressure, and the temperature of the CO 2 capture reactions by Na 2-α M α ZrO 3 , and from thermogravimetric-analysis experimental measurements, the Li- and K-doped mixtures Na 2-α M α ZrO 3 have lower turnover temperatures (T t ) and higher CO 2 capture capacities, compared to pure Na 2 ZrO 3 . The Li-doped systems have a larger T t decrease than the K-doped systems. When increasing the Li-doping level α, the T t of the corresponding mixture Na 2-α Li α ZrO 3 decreases further to a low-temperature range. However, in the case of K-doped systems Na 2-α K α ZrO 3 , although doping K into Na 2 ZrO 3 initially shifts its T t to lower temperatures, further increases of the K-doping level α causes T t to increase. Therefore, doping Li into Na 2 ZrO 3 has a larger influence on its CO 2 capture performance than the K-doped Na 2 ZrO 3 . Compared with pure solidsM 2 ZrO 3 , after doping with other elements, these doped systems’ CO 2 capture performances are improved.
Duan, Yuhua↗
Electron-electron interactions and weak antilocalization in few-layer ZrTe 5 devices
Recently, a lot of efforts have been devoted to the transport properties of relatively thick ZrTe 5 crystals, focusing on their three-dimensional topological effects. ZrTe 5 in its 2D limit, on the other hand, was much less explored experimentally. Here we present detailed magnetotransport studies of few-layer ZrTe 5 devices, in which the coexistence of strong electron-electron interaction and weak anti-localization is observed. The coexistence of the two effects manifests itself in the temperature and magnetic field dependence of the resistance as well as in the universal conductance fluctuations of the few-layer devices. Both effects also show strong two dimensional characteristics. Finally, our results provide new insight into the highly intricate properties of topological material ZrTe 5 .
2-dimensional systems↗
Electronic structure and x-ray magnetic circular dichroism in YbAgCu4 and YbInCu4
X-ray absorption and magnetic circular dichroism spectra at the L-3 edge of Yb have been studied theoretically in the mixed-valent compounds YbAgCu4 and YbInCu4 using the fully relativistic Dirac linear muffin-tin orbital band structure method. The effect of the spin-orbit (SO) interaction and Coulomb repulsion U on the electronic structure of YbAgCu4 and YbInCu4 is examined in the frame of the local spin-density approximation (LSDA)+SO+U method. The core-hole effect in the final states as well as the effect of the electric quadrupole E-2 and magnetic dipole M-1 transitions have been investigated. The calculated results are compared with available experimental data.
Antonov, VN↗
Effect of electron correlation on the electronic structure and spin-lattice coupling of high- T c cuprates: Quantum Monte Carlo calculations
Electron correlation effects are particularly strong in high-temperature superconducting materials. Devising an accurate description of these materials has long been a challenge, with these strong correlation effects historically being considered impossible or impractical to simulate computationally. Using quantum Monte Carlo techniques, we have explicitly simulated electron correlations in several cuprate materials from first principles. These simulations accurately reproduce many important physical quantities of these materials, including the interaction-induced gap and superexchange coupling between copper spins, with no additional parameters beyond fundamental constants. We further investigate the dimensionless spin-lattice coupling parameter in the parent materials, showing that it varies dramatically, between 0.1 and 1.0, depending on the interlayer. Furthermore, this result indicates that the lattice and magnetic degrees of freedom are not independent in these systems, which may have ramifications for the origin of superconductivity.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Symmetry-dependent electron-electron interaction in coherent tunnel junctions resolved by measurements of zero-bias anomaly
We provide experimental evidence that zero bias anomaly in the differential resistance of magnetic tunnel junctions (MTJs) is due to electron-electron interaction (EEI). Magnon effect is excluded by measuring at low temperatures down to 0.2 K and with reduced AC measurement voltages down to 0.06 mV. The normalized change of conductance is proportional to ln (eV /k B T ), consistent with the Altshuler-Aronov theory of tunneling with EEI but inconsistent with magnetic impurity scattering. The slope of the ln (eV /k B T ) dependence is symmetry dependent, i.e., MTJs with symmetry filtering show di erent slopes for P and AP states, while those without symmetry filtering (amorphous barriers) have nearly the same slopes for P and AP.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Strongly coupled electronic, magnetic, and lattice degrees of freedom in LaCo[subscript 5] under pressure
Abstract not provided
Stillwell, Ryan L.↗
Raman scattering study of spin-density-wave-induced anisotropic electronic properties in A Fe 2 As 2 ( A = Ca , Eu)
We present a polarization-resolved and temperature-dependent Raman scattering study of AFe 2 As 2 (A = Ca, Eu). In the spin-density-wave phase, spectral weight redistribution is observed in the fully symmetric and nonsymmetric scattering channels at different energies. An anisotropic Raman response is observed in the fully symmetric channel in spontaneously detwinned CaFe 2 As 2 samples. We calculate the orbital-resolved electronic structures using a combination of density functional theory and dynamical mean field theory. We identify the electronic transitions corresponding to these two spectral features and find that the anisotropic Raman response originates from the lifted degeneracy of the d xz/yz orbitals in the broken-symmetry phase.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Disordered dimer state in electron-doped Sr 3 Ir 2 O 7
Spin excitations are explored in the electron-doped spin-orbit Mott insulator (Sr 1-x La x ) 3 Ir 2 O 7 . As this bilayer square lattice system is doped into the metallic regime, long-range antiferromagnetism vanishes, yet a spectrum of gapped spin excitation remains. Excitation lifetimes are strongly damped with increasing carrier concentration, and the energy-integrated spectral weight becomes nearly momentum independent as static spin order is suppressed. Local magnetic moments, absent in the parent system, grow in metallic samples and approach values consistent with one J=12 impurity per electron doped. Our combined data suggest that the magnetic spectra of metallic (Sr 1-x La x ) 3 Ir 2 O 7 are best described by excitations out of a disordered dimer state.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Electronic and magnetic properties of epitaxial SrRh O 3 films
The strong interplay of fundamental order parameters in complex oxides is known to give rise to exotic physical phenomena. The 4$d$ transition-metal oxide SrRh O 3 has generated much interest, but advances have been hindered by difficulties in preparing single-crystalline phases. Here we epitaxially stabilize high-quality single-crystalline SrRh O 3 films and investigate their structural, electronic, and magnetic properties. Lastly, we determine that their properties significantly differ from the paramagnetic metallic ground state that governs bulk samples and are strongly related to rotations of Rh O 6 octahedra.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Geometry and electronic structure of iridium adsorbed on graphene
We report investigation of the geometry and electronic structure of iridium atoms adsorbed onto graphene through a combined experimental and theoretical study. Ir atoms were deposited onto a flake of graphene on a Pt(111) surface and found to form clusters even at low temperatures. The areal density of the observed clusters on the graphene flake suggests the clusters are most likely pairs of Ir atoms. Theoretical ab initio density functional (DFT) calculations indicate that these Ir dimers are oriented horizontally, near neighboring "bridge" sites of the graphene lattice, as this configuration has the strongest adsorption energy of all high-symmetry configurations for the Ir dimer. A large peak in the local density of states (LDOS) at the Dirac point energy was measured via scanning tunneling spectroscopy, and this result is reproduced by a DFT calculation of the LDOS. The peak at the Dirac point energy is found to be from the Ir s and p states. Finally, the LDOS in the monomer case was also calculated, and is found to significantly differ from the experimentally determined data, further supporting the hypothesis of low-temperature clustering.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Electron capture decay of 58-min U-229(92) and levels in Pa-229(91)
Electron capture decay of U-229 is investigated by measuring the gamma-ray and conversion electron spectra of mass-separated and unseparated U-229 sources with high-resolution germanium and silicon detectors, respectively. Gamma-gamma coincidence measurements are also performed using germanium detectors. These studies provide level energies and level ordering in Pa-229. Single-particle assignments are given to these levels which are in agreement with the systematics in this region and also with theory. In a previous study, we report the observation of a 5/2(+/-) parity doublet in the Pa-229 ground state, which is a signature of octupole deformation. The present analysis of the data still shows a splitting of 60 +/- 50 eV, but with this large uncertainty the existence of the doublet is not certain.
Ahmad, I.↗
Target and beam-target spin asymmetries in exclusive π + and π - electroproduction with 1.6- to 5.7-GeV electrons
Beam-target double-spin asymmetries and target single-spin asymmetries in exclusive pi(+) and quasiexclusive pi(-) electroproduction were obtained from scattering of 1.6- to 5.7-GeV longitudinally polarized electrons from longitudinally polarized protons (for pi(+)) and deuterons (for pi(-)) using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. The kinematic range covered is 1.1 < W < 2.6 GeV and 0.05 < Q(2) < 5 GeV2, with good angular coverage in the forward hemisphere. The asymmetry results were divided into approximately 40 000 kinematic bins for pi(+) from free protons and 15 000 bins for pi(-) production from bound nucleons in the deuteron. The present results are found to be in reasonable agreement with fits to previous world data for W < 1.7 GeV and Q(2) < 0.5 GeV2, with discrepancies increasing at higher values of Q(2), especially for W > 1.5 GeV. Very large target-spin asymmetries are observed for W > 1.6 GeV. When combined with cross-section measurements, the present results can provide powerful constraints on nucleon resonance amplitudes at moderate and large values of Q(2), for resonances with masses as high as 2.3 GeV.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗