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Physics Faculty Research & Creative Works

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Full-Text Articles in Physical Sciences and Mathematics

Screened-Exchange Determination Of The Electronic Properties Of Monoclinic, Tetragonal And Cubic Zirconia, Julia E. Medvedeva, C. B. Geller, D. M. Rishel, Arthur J. Freeman Jan 2007

Screened-Exchange Determination Of The Electronic Properties Of Monoclinic, Tetragonal And Cubic Zirconia, Julia E. Medvedeva, C. B. Geller, D. M. Rishel, Arthur J. Freeman

Physics Faculty Research & Creative Works

First-principles electronic band structure investigations of monoclinic, tetragonal, and cubic ZrO2 reveal the highly anisotropic nature of the conduction and valence band topologies in the monoclinic phase with electron and hole effective masses differing by over an order of magnitude in perpendicular directions. The planes of relatively high implied electron and hole mobilities intersect along a single crystallographic direction, making this the only direction readily available for exciton motion. Conversely, in the tetragonal and cubic phases, charge carrier effective masses are more isotropic and exciton motion is less restricted. These findings may explain recent experimental observations suggesting that exciton production …

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Spatial Distribution And Magnetism In Poly-Cr-Doped Gan From First Principles, X. Y. Cui, Julia E. Medvedeva, B. Delley, C. Stampfl, Arthur J. Freeman Jan 2007

Spatial Distribution And Magnetism In Poly-Cr-Doped Gan From First Principles, X. Y. Cui, Julia E. Medvedeva, B. Delley, C. Stampfl, Arthur J. Freeman

Physics Faculty Research & Creative Works

Large scale density-functional theory calculations have been performed to understand the spatial distribution and magnetic coupling of Cr-doped GaN, in which exhaustive structural and magnetic configurations have been investigated by doping of up to five Cr atoms in large supercells. Our results provide direct evidence that the distribution of the doped magnetic ions is neither homogeneous nor random as widely assumed previously. Rather, under both Ga-rich and N-rich growth conditions, the Cr atoms have a strong tendency to form substitutional, embedded clusters with short-range magnetic interactions maintaining the wurtzite structure. Significantly, while the ferromagnetic state is favored for pair doping, …

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Photon Angular Distribution And Nuclear-State Alignment In Nuclear Excitation By Electron Capture, Adriana Palffy, Zoltan Harman, Andrey S. Surzhykov, Ulrich D. Jentschura Jan 2007

Photon Angular Distribution And Nuclear-State Alignment In Nuclear Excitation By Electron Capture, Adriana Palffy, Zoltan Harman, Andrey S. Surzhykov, Ulrich D. Jentschura

Physics Faculty Research & Creative Works

The alignment of nuclear states resonantly formed in nuclear excitation by electron capture (NEEC) is studied by means of a density matrix technique. The vibrational excitations of the nucleus are described by a collective model and the electrons are treated in a relativistic framework. Formulas for the angular distribution of photons emitted in the nuclear relaxation are derived. We present numerical results for alignment parameters and photon angular distributions for a number of heavy elements in the case of E2 nuclear transitions. Our results are intended to help future experimental attempts to discern NEEC from radiative recombination, which is the …

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Evidence Of Dynamical Spin Shielding In Ce From Spin-Resolved Photoelectron Spectroscopy, James G. Tobin, S. W. Yu, Takashi Komesu, B. W. Chung, Simon A. Morton, George Daniel Waddill Jan 2007

Evidence Of Dynamical Spin Shielding In Ce From Spin-Resolved Photoelectron Spectroscopy, James G. Tobin, S. W. Yu, Takashi Komesu, B. W. Chung, Simon A. Morton, George Daniel Waddill

Physics Faculty Research & Creative Works

Using Fano effect measurements upon polycrystalline Ce, we have observed a phase reversal between the spectral structure at the Fermi edge and the other 4f derived feature near a binding energy of 2 eV. The Fano effect is the observation of spin polarized photoelectron emission from nonmagnetic materials, under chirally selective excitation, such as circularly polarized photons. The observation of phase reversal between the two peaks is a direct experimental proof of Kondo shielding in Ce, confirming the predictions of Gunnarsson and Shoenhammer, albeit with a small modification.

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Effects Of Dissipation On A Quantum Critical Point With Disorder, Jose A. Hoyos, Chetan Kotabage, Thomas Vojta Jan 2007

Effects Of Dissipation On A Quantum Critical Point With Disorder, Jose A. Hoyos, Chetan Kotabage, Thomas Vojta

Physics Faculty Research & Creative Works

We study the effects of dissipation on a disordered quantum phase transition with O(N) order-parameter symmetry by applying a strong-disorder renormalization group to the Landau-Ginzburg-Wilson field theory of the problem. We find that Ohmic dissipation results in a nonperturbative infinite-randomness critical point with unconventional activated dynamical scaling while super-Ohmic damping leads to conventional behavior. We discuss applications to the superconductor-metal transition in nanowires and to the Hertz theory of the itinerant antiferromagnetic transition.

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Local Defect In A Magnet With Long-Range Interactions, Jose A. Hoyos, Thomas Vojta Jan 2007

Local Defect In A Magnet With Long-Range Interactions, Jose A. Hoyos, Thomas Vojta

Physics Faculty Research & Creative Works

We investigate a single defect coupling to the square of the order parameter in a nearly critical magnet with long-range spatial interactions of the form r−(d+sigma), focusing on magnetic droplets nucleated at the defect while the bulk system is in the paramagnetic phase. To determine the static droplet profile, we solve a Landau-Ginzburg-Wilson action in the saddle-point approximation. Because of the long-range interaction, the droplet develops a power-law tail which is energetically unfavorable. However, as long as sigma>0, the tail contribution to the droplet free energy is subleading in the limit of large droplets; and the free energy becomes …

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Angular Distributions From Photoionization Of H₂⁺, J. Colgan, O. Al-Hagan, Jerry Peacher, Don H. Madison, M. S. Pindzola, M. Foster Jan 2007

Angular Distributions From Photoionization Of H₂⁺, J. Colgan, O. Al-Hagan, Jerry Peacher, Don H. Madison, M. S. Pindzola, M. Foster

Physics Faculty Research & Creative Works

A study is made of the differential cross sections arising from the photoionization of H2+. Previous studies indicated surprising differences in the shapes of the angular distributions calculated from exterior complex scaling and 2C methods. To further explore these differences, we have calculated the angular distributions from the photoionization of H2+ using an independent two-body Coulomb function (2C) method and a distorted wave approach. As a final test, we also present calculations using a time-dependent technique. Our results confirm the discrepancies found previously and we present possible reasons for these differences.

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Differential Double Capture Cross Sections In P+He Collisions, Michael Schulz, T. Vajnai, J. A. Brand Jan 2007

Differential Double Capture Cross Sections In P+He Collisions, Michael Schulz, T. Vajnai, J. A. Brand

Physics Faculty Research & Creative Works

We have measured differential double capture cross sections for 15 to 150 keV p+He collisions. We also analyzed differential double to single capture ratios, where we find pronounced peak structures. An explanation of these structures probably requires a quantum-mechanical description of elastic scattering between the projectile and the target nucleus. Strong final-state correlations have a large effect on the magnitude of the double capture cross sections

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Effects Of The Final-State Electron-Ion Interactions On The Fully Differential Cross Sections For Heavy-Particle-Impact Ionization Of Helium, Don H. Madison, Jerry Peacher, M. Foster, K. Bartschat, H. P. Saha, Allison L. Harris Jan 2007

Effects Of The Final-State Electron-Ion Interactions On The Fully Differential Cross Sections For Heavy-Particle-Impact Ionization Of Helium, Don H. Madison, Jerry Peacher, M. Foster, K. Bartschat, H. P. Saha, Allison L. Harris

Physics Faculty Research & Creative Works

Three-dimensional fully differential cross sections for heavy-particle-impact ionization of helium are examined. Previously, the three-body distorted-wave (3DW) model has achieved good agreement with experiment in the scattering plane for small momentum transfers, but poor agreement for large momentum transfers. Poor agreement was also observed outside the scattering plane for all momentum transfers. In particular, the 3DW calculations predicted cross sections that were too small both perpendicular to the scattering plane and for large momentum transfers. The important unanswered question concerns the physical effects that cause the significant disagreement between experiment and theory. In previous works, the role of the projectile-ion …

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Evaluation Of Laser-Assisted Bremsstrahlung With Dirac-Volkov Propagators, Erik Lotstedt, Ulrich D. Jentschura, Christoph H. Keitel Jan 2007

Evaluation Of Laser-Assisted Bremsstrahlung With Dirac-Volkov Propagators, Erik Lotstedt, Ulrich D. Jentschura, Christoph H. Keitel

Physics Faculty Research & Creative Works

We study spontaneous bremsstrahlung emission in a highly intense laser field. In this regime the interaction with the laser field has to be treated nonperturbatively by using the relativistic formalism including Dirac-Volkov propagators, while the interaction with the Coulomb field and the bremsstrahlung radiation can be treated in first-order perturbation theory. For the intermediate electron state a fully laser-dressed propagator is used, including radiative corrections to avoid singularities on the mass shell. We find that the use of the Dirac-Volkov propagator is crucial to obtain correct numerical results. The cross section of the process is evaluated for laser intensities of …

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Erratum: Evaluation Of Laser-Assisted Bremsstrahlung With Dirac-Volkov Propagators (Physical Review Letters (2007) 98 (043002)), Erik Lotstedt, Ulrich D. Jentschura, Christoph H. Keitel Jan 2007

Erratum: Evaluation Of Laser-Assisted Bremsstrahlung With Dirac-Volkov Propagators (Physical Review Letters (2007) 98 (043002)), Erik Lotstedt, Ulrich D. Jentschura, Christoph H. Keitel

Physics Faculty Research & Creative Works

No abstract provided.

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Reconciliation Of Measured Fully Differential Single Ionization Data With The First Born Approximation Convoluted With Elastic Scattering, Michael Schulz, M. Dürr, B. Najjari, R. Moshammer, J. D. Ullrich Jan 2007

Reconciliation Of Measured Fully Differential Single Ionization Data With The First Born Approximation Convoluted With Elastic Scattering, Michael Schulz, M. Dürr, B. Najjari, R. Moshammer, J. D. Ullrich

Physics Faculty Research & Creative Works

An analysis of experimental fully differential data for single ionization in 100 MeV/amu C6++He collisions is reported. We present a convolution of the first Born approximation with elastic scattering by using an event generator technique. Furthermore, the calculation is convoluted with all known experimental resolutions. Our analysis shows that elastic scattering is a viable explanation for surprising structures observed in the fully differential cross sections outside the scattering plane. Furthermore, it may even explain discrepancies in the “recoil peak” frequently observed for both ion and electron impact.

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Quantum-Theory Based Event Generator For The Analysis Of Kinematically Complete Experiments, M. Dürr, B. Najjari, Michael Schulz, A. Dorn, R. Moshammer, J. Ullrich Jan 2007

Quantum-Theory Based Event Generator For The Analysis Of Kinematically Complete Experiments, M. Dürr, B. Najjari, Michael Schulz, A. Dorn, R. Moshammer, J. Ullrich

Physics Faculty Research & Creative Works

The 'reaction microscope', an electron-ion coincidence momentum imaging spectrometer, represents a unique technique to measure multiply differential ionization cross sections for ionic projectiles. Observed discrepancies with theory for singly ionizing collision of 3.6 MeV/u Au53+ and 100 MeV/u C6+ ions severely challenge theoretical models. We present a method based on event-generators, which allows to consistently incorporate instrumental effects into theory. The result of the convolution procedure suggests, that the observed discrepancies are not a result of the experimental resolution, but are of true physical nature.

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Averaging Of The Electron Effective Mass In Multicomponent Transparent Conducting Oxides, Julia E. Medvedeva Jan 2007

Averaging Of The Electron Effective Mass In Multicomponent Transparent Conducting Oxides, Julia E. Medvedeva

Physics Faculty Research & Creative Works

We find that layered materials composed of various oxides of cations with s2 electronic configuration, XY2O4, X = in or Sc, Y = Ga, Zn, Al, Cd and/or Mg, exhibit isotropic electron effective mass which can be obtained via averaging over those of the corresponding single-cation oxide constituents. This effect is due to a hybrid nature of the conduction band formed from the s-states of all cations and the oxygen p-states. Moreover, the observed insensitivity of the electron effective mass to the oxygen coordination and to the distortions in the cation-oxygen chains suggests that a …

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Normal Transport At Positive Temperatures In Classical Hamiltonian Open Systems, P. Lafitte, Paul Ernest Parris, Stephan De Bièvre Jan 2007

Normal Transport At Positive Temperatures In Classical Hamiltonian Open Systems, P. Lafitte, Paul Ernest Parris, Stephan De Bièvre

Physics Faculty Research & Creative Works

We study the transport properties of classical Hamiltonian models describing the motion of an unconfined particle coupled to vibrational degrees of freedom in thermal equilibrium at zero or positive temperature. We identify and discuss conditions under which, in such systems, the particle has a well-defined diffusion constant and mobility. We will in particular point out some marked differences with the situation where the particle is confined and described with a Caldeira-Leggett model. We will more specifically report on results obtained in a classical version of the Holstein molecular crystal model, speculate on their relevance in the corresponding quantum system and …

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An Investigation Of Thundersnow And Deep Snow Accumulations, Christina Crowe, Patrick Market, Brian Pettergrew, Chris Melick, Josef Podzimek Dec 2006

An Investigation Of Thundersnow And Deep Snow Accumulations, Christina Crowe, Patrick Market, Brian Pettergrew, Chris Melick, Josef Podzimek

Physics Faculty Research & Creative Works

A comparison of 30 years of hourly surface weather observations (1960-1991) from first-order stations and 24-hour snowfall data from climate network stations over the upper Midwestern United States reveals an indirect association between the relatively rare occurrence of thundersnow (< 1 event yr-1 in this dataset) and the accumulation of significant 24-hour snowfall (> 15 cm) in 19 of 22 cases identified. Although no direct relationship is found between the location of thundersnow and the deepest 24-hour snow totals, significant snow accumulations frequently occurred in proximity (< 1° latitude) to thundersnow events. the presence of thundersnow tended to indicate a parent extratropical cyclone capable of producing significant snowfall totals; should thundersnow be anticipated, the operational meteorologist can have much greater confidence in forecasting deeper snow totals. Copyright 2006 by the American Geophysical Union.

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Two-Loop Bethe Logarithms For Non- S Levels, Ulrich D. Jentschura Dec 2006

Two-Loop Bethe Logarithms For Non- S Levels, Ulrich D. Jentschura

Physics Faculty Research & Creative Works

Two-loop Bethe logarithms are calculated for excited P and D states in hydrogenlike systems, and estimates are presented for all states with higher angular momenta. These results complete our knowledge of the P and D energy levels in hydrogen at the order of α8 mec2, where me is the electron mass and c is the speed of light, and scale as Z6, where Z is the nuclear charge number. Our analytic and numerical calculations are consistent with the complete absence of logarithmic terms of order (απ)2 (Zα)6 ln [(Zα)-2] …

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Differential Electron Emission For Single And Multiple Ionization Of Argon By 500 Ev Positrons, Jared M. Gavin, Robert D. Dubois, O. G. De Lucio Dec 2006

Differential Electron Emission For Single And Multiple Ionization Of Argon By 500 Ev Positrons, Jared M. Gavin, Robert D. Dubois, O. G. De Lucio

Physics Faculty Research & Creative Works

Triply differential electron emission cross sections are measured for single ionization of argon by 500 eV positrons. Data are presented for coincidences between projectiles scattered into angles of 3° and electrons with emission energies less than 10 eV that are observed between 45 and 135° along the beam direction. For interpretation, these are compared to cosine squared representations of the binary and recoil lobes which are convoluted over experimental parameters. Singly differential electron emission data for double and triple ionization by positrons are also presented.

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Facile Syntheses Of Monodisperse Ultrasmall Au Clusters, Massimo F. Bertino, Zhong Ming Sun, Rui Zhang, Lai Sheng Wang Nov 2006

Facile Syntheses Of Monodisperse Ultrasmall Au Clusters, Massimo F. Bertino, Zhong Ming Sun, Rui Zhang, Lai Sheng Wang

Physics Faculty Research & Creative Works

During our effort to synthesize the tetrahedral Au20 cluster, we found a facile synthetic route to prepare monodisperse suspensions of ultrasmall Au clusters AuN (N < 12) using diphosphine ligands. in our monophasic and single-pot synthesis, an Au precursor ClAu(I)PPh3 (Ph = phenyl) and a bidentate phosphine ligand P(Ph)2(CH 2) M (Ph)2 are dissolved in an organic solvent. Au(I) is reduced slowly by a borane-tert-butylamine complex to form Au clusters coordinated by the diphosphine ligand. the Au clusters are characterized by both high-resolution mass spectrometry and UV-vis absorption spectroscopy. We found that the mean cluster size obtained depends on the chain length M of the ligand. in particular, a single monodispersed Au11 cluster is obtained with the P(Ph)2(CH2)3P(Ph)2 ligand, whereas P(Ph)2(CH2) MP (Ph)2 ligands with M = 5 and 6 yield Au10 and Au8 clusters. the simplicity of our synthetic method makes it suitable for large-scale production of nearly monodisperse ultrasmall Au clusters. It is suggested that diphosphines provide a set of flexible ligands to allow size-controlled synthesis of Au nanoparticles. © 2006 American Chemical Society.

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Quantum Dot Potentials: Symanzik Scaling, Resurgent Expansions, And Quantum Dynamics, Andrey S. Surzhykov, Michael Lubasch, Jean Zinn-Justin, Ulrich D. Jentschura Nov 2006

Quantum Dot Potentials: Symanzik Scaling, Resurgent Expansions, And Quantum Dynamics, Andrey S. Surzhykov, Michael Lubasch, Jean Zinn-Justin, Ulrich D. Jentschura

Physics Faculty Research & Creative Works

This article is concerned with a special class of the "double-well- like" potentials that occur naturally in the analysis of finite quantum systems. Special attention is paid, in particular, to the so-called Fokker-Planck potential, which has a particular property: the perturbation series for the ground-state energy vanishes to all orders in the coupling parameter, but the actual ground-state energy is positive and dominated by instanton configurations of the form exp (-a g), where a is the instanton action. The instanton effects are most naturally taken into account within the modified Bohr-Sommerfeld quantization conditions whose expansion leads to the generalized perturbative …

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Analysis Of Two-Dimensional Photoelectron Momentum Spectra And The Effect Of The Long-Range Coulomb Potential In Single Ionization Of Atoms By Intense Lasers, Zhangjin Chen, Toru Morishita, Anh-Thu Le, M. Wickenhauser, X. M. Tong, C. D. Lin Nov 2006

Analysis Of Two-Dimensional Photoelectron Momentum Spectra And The Effect Of The Long-Range Coulomb Potential In Single Ionization Of Atoms By Intense Lasers, Zhangjin Chen, Toru Morishita, Anh-Thu Le, M. Wickenhauser, X. M. Tong, C. D. Lin

Physics Faculty Research & Creative Works

Two-dimensional (2D) electron momentum distributions and energy spectra for multiphoton ionization of atoms by intense laser pulses, calculated by solving the time-dependent Schrödinger equation (TDSE) for different wavelengths and intensities, are compared to those predicted by the strong-field approximation (SFA). It is shown that the momentum spectra at low energies between the TDSE and SFA are quite different and the differences arise largely from the absence of a long-range Coulomb interaction in the SFA. We further found that the low-energy 2D momentum spectra from the TDSE exhibit ubiquitous fanlike features where the number of stripes is due to a single …

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K Α₁ Radiation From Heavy, Heliumlike Ions Produced In Relativistic Collisions, Andrey S. Surzhykov, Ulrich D. Jentschura, Th H. Stohlker, Stephan Fritzsche Nov 2006

K Α₁ Radiation From Heavy, Heliumlike Ions Produced In Relativistic Collisions, Andrey S. Surzhykov, Ulrich D. Jentschura, Th H. Stohlker, Stephan Fritzsche

Physics Faculty Research & Creative Works

Bound-state transitions in few-electron, heavy ions following radiative electron capture are studied within the framework of the density matrix theory and the multiconfiguration Dirac-Fock approach. Special attention is paid to the K α1 (1 s1/2 2 p3/2 1.3PJ=1,2→1s21/2 1SJ=0) radiative decay of heliumlike uranium U90+ projectiles. This decay has recently been observed at the GSI facility in Darmstadt, giving rise to a surprisingly isotropic angular distribution, which is inconsistent with previous experiments and calculations based on a "one-particle" model. We show that the unexpected isotropy essentially results from …

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Multiple Scattering Mechanisms In Simultaneous Projectile-Electron And Target-Electron Ejection In H⁻ + He Collisions, Michael Schulz, T. Ferger, Daniel Fischer, R. Moshammer, J. D. Ullrich Oct 2006

Multiple Scattering Mechanisms In Simultaneous Projectile-Electron And Target-Electron Ejection In H⁻ + He Collisions, Michael Schulz, T. Ferger, Daniel Fischer, R. Moshammer, J. D. Ullrich

Physics Faculty Research & Creative Works

We studied simultaneous electron ejection from both collision partners in 200-keV H-+He collisions in a kinematically complete experiment by measuring the fully momentum-analyzed recoil ions and both active electrons in coincidence. The data were analyzed in terms of Dalitz spectra, in which the momentum exchange between three particles is plotted simultaneously in a single spectrum. We found that the energy transfer occurs predominantly between the active electrons, but most of the momentum is exchanged in elastic scattering between the cores of the collision partners.

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Gravitational Diffraction Radiation, Vitor Cardoso, Marco Cavaglia, Mario Pimenta Oct 2006

Gravitational Diffraction Radiation, Vitor Cardoso, Marco Cavaglia, Mario Pimenta

Physics Faculty Research & Creative Works

We show that if the visible universe is a membrane embedded in a higher-dimensional space, particles in uniform motion radiate gravitational waves because of spacetime lumpiness. This phenomenon is analogous to the electromagnetic diffraction radiation of a charge moving near to a metallic grating. In the gravitational case, the role of the metallic grating is played by the inhomogeneities of the extra-dimensional space, such as a hidden brane. We derive a general formula for gravitational diffraction radiation and apply it to a higher-dimensional scenario with flat compact extra dimensions. Gravitational diffraction radiation may carry away a significant portion of the …

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Volumes Of Critical Bubbles From The Nucleation Theorem, Gerald Wilemski Sep 2006

Volumes Of Critical Bubbles From The Nucleation Theorem, Gerald Wilemski

Physics Faculty Research & Creative Works

A corollary of the nucleation theorem due to Kashchiev [Nucleation: Basic Theory with Applications (Butterworth-Heinemann, Oxford, 2000)] allows the volume V* of a critical bubble to be determined from nucleation rate measurements. The original derivation was limited to one-component, ideal gas bubbles with a vapor density much smaller than that of the ambient liquid. Here, an exact result is found for multicomponent, nonideal gas bubbles. Provided a weak density inequality holds, this result reduces to Kashchiev's simple form which thus has a much broader range of applicability than originally expected. Limited applications to droplets are also mentioned, and the utility …

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Exploring Relativistic Many-Body Recoil Effects In Highly Charged Ions, R. Soria Orts, Zoltan Harman, Jose R. Crespo Lopez-Urrutia, Anton N. Artemyev, Hjalmar Bruhns, Antonio J. Gonzalez, Ulrich D. Jentschura, Christoph H. Keitel, Alain Lapierre, Vladimir Sergeyevich Mironov, Vladimir M. Shabaev, Hiroyuki Tawara, I. I. Tupitsyn, Joachim Hermann Ullrich, Andrey V. Volotka Sep 2006

Exploring Relativistic Many-Body Recoil Effects In Highly Charged Ions, R. Soria Orts, Zoltan Harman, Jose R. Crespo Lopez-Urrutia, Anton N. Artemyev, Hjalmar Bruhns, Antonio J. Gonzalez, Ulrich D. Jentschura, Christoph H. Keitel, Alain Lapierre, Vladimir Sergeyevich Mironov, Vladimir M. Shabaev, Hiroyuki Tawara, I. I. Tupitsyn, Joachim Hermann Ullrich, Andrey V. Volotka

Physics Faculty Research & Creative Works

The relativistic recoil effect has been the object of experimental investigations using highly charged ions at the Heidelberg electron beam ion trap. Its scaling with the nuclear charge Z boosts its contribution to a measurable level in the magnetic-dipole (M1) transitions of B- and Be-like Ar ions. The isotope shifts of 36Ar versus 40Ar have been detected with sub-ppm accuracy, and the recoil effect contribution was extracted from the 1s22s22p 2P1/2-2P3/2 transition in Ar13+ and the 1s22s2p 3P1-3P2 transition …

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Hyperspherical Close-Coupling Calculations For Electron-Capture Cross Sections In Low-Energy Ne¹⁰⁺ +H (1s) Collisions, P. Barragan, Anh-Thu Le, C. D. Lin Jul 2006

Hyperspherical Close-Coupling Calculations For Electron-Capture Cross Sections In Low-Energy Ne¹⁰⁺ +H (1s) Collisions, P. Barragan, Anh-Thu Le, C. D. Lin

Physics Faculty Research & Creative Works

We present total and partial electron-capture cross sections for Ne¹⁰⁺ +H (1s) collisions at energies from 0.01 eV to 1 keV using the hyperspherical close-coupling method. Good agreements with the previous calculations by the classical-trajectory Monte-Carlo method are found for total capture cross section, but not for partial cross sections, especially below about 200 eV/amu. We found that the total cross section is mainly due to the population of n=7 channels and only at energies above 50 eV/amu n = 5,6 channels begin to contribute to the total cross section.

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Polarization-Operator Approach To Electron-Positron Pair Production In Combined Laser And Coulomb Fields, A. I. Milstein, Carsten Muller, Karen Z. Hatsagortsyan, Ulrich D. Jentschura, Christoph H. Keitel Jun 2006

Polarization-Operator Approach To Electron-Positron Pair Production In Combined Laser And Coulomb Fields, A. I. Milstein, Carsten Muller, Karen Z. Hatsagortsyan, Ulrich D. Jentschura, Christoph H. Keitel

Physics Faculty Research & Creative Works

The optical theorem is applied to the process of electron-positron pair creation in the superposition of a nuclear Coulomb and a strong laser field. We derive representations for the total production rate as twofold integrals, both for circular laser polarization and for the general case of elliptic polarization. Our approach allows us to obtain, by analytical means, the asymptotic behavior of the pair creation rate for various limits of interest. In particular, we consider pair production by two-photon absorption and show that, close to the energetic threshold of this process, the rate obeys a power law in the laser frequency …

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Young-Type Interference In (E, 2e) Ionization Of H₂, D. S. Milne-Brownlie, Matthew S. Foster, Junfang Gao, B. Lohmann, Don H. Madison Jun 2006

Young-Type Interference In (E, 2e) Ionization Of H₂, D. S. Milne-Brownlie, Matthew S. Foster, Junfang Gao, B. Lohmann, Don H. Madison

Physics Faculty Research & Creative Works

We have investigated the electron impact single ionization of the hydrogen molecule, with fully determined kinematics. The experimental and theoretical results are compared with He ionization under the same conditions. The results indicate that the ejected electron angular distribution for H2 is modified due to Young-type interference between ionization amplitudes for scattering from the two centers in the hydrogen molecule. The observable result is a suppression of the backward scattering (recoil) peak compared with the binary peak.

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Quantum Electrodynamic Corrections To The Hyperfine Structure Of Excited S States, Ulrich D. Jentschura, Vladimir A. Yerokhin Jun 2006

Quantum Electrodynamic Corrections To The Hyperfine Structure Of Excited S States, Ulrich D. Jentschura, Vladimir A. Yerokhin

Physics Faculty Research & Creative Works

State-dependent quantum electrodynamic corrections are evaluated for the hyperfine splitting of nS states for arbitrary principal quantum number n. The calculations comprise both the self-energy and the vacuum-polarization correction of order α(Zα) 2 EF and the recoil correction of order (Zα)2 (m/M) EF. Higher-order corrections are summarized and partly reevaluated as well. Accurate predictions for hydrogen hyperfine splitting intervals of nS states with n=2,...,8 are presented. The results obtained are important due to steady progress in hydrogen spectroscopy for transitions involving highly excited S states.

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