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Articles 31 - 52 of 52
Full-Text Articles in Physical Sciences and Mathematics
Two-Center Double-Capture Interference In Fast H E²⁺+ H₂ Collisions, Deepankar S. Misra, Henning T. Schmidt, M. Gudmundsson, Daniel Fischer, Nicole Haag, Henrik A B Johansson, Anders Kallberg, B. Najjari, Peter Reinhed, Reinhold S. Schuch, Markus S. Schoffler, Ansgar Simonsson, Alexander B. Voitkiv, Henrik Cederquist
Two-Center Double-Capture Interference In Fast H E²⁺+ H₂ Collisions, Deepankar S. Misra, Henning T. Schmidt, M. Gudmundsson, Daniel Fischer, Nicole Haag, Henrik A B Johansson, Anders Kallberg, B. Najjari, Peter Reinhed, Reinhold S. Schuch, Markus S. Schoffler, Ansgar Simonsson, Alexander B. Voitkiv, Henrik Cederquist
Physics Faculty Research & Creative Works
We report the first observation of Young-type interference effects in a two-electron transfer process. These effects change strongly as the projectile velocity changes in fast (1.2 and 2.0 MeV) He2++H2 collisions as manifested in strong variations of the double-electron capture rates with the H2 orientation. This is consistent with fully quantum mechanical calculations, which ignore sequential electron transfer, and a simple projectile de Broglie wave picture assuming that two-electron transfer probabilities are higher in collisions where the projectile passes close to either one of the H2 nuclei.
Role Of Elastic Projectile-Electron Scattering In Double Ionization Of Helium By Fast Proton Impact, Michael Schulz, M. F. Ciappina, T. Kirchner, Daniel Fischer, R. Moshammer, J. D. Ullrich
Role Of Elastic Projectile-Electron Scattering In Double Ionization Of Helium By Fast Proton Impact, Michael Schulz, M. F. Ciappina, T. Kirchner, Daniel Fischer, R. Moshammer, J. D. Ullrich
Physics Faculty Research & Creative Works
We present a systematic study of atomic four-body fragmentation dynamics. To this end we have measured a variety of multiple differential double ionization cross sections for 6 MeV p+He collisions. The data are compared to a first-order calculation with correlated electrons and to a simulation representing a second-order process, with some experimental results seemingly in favor of the first, others in agreement with the second approach. This apparent conflict can be resolved by accounting for elastic scattering between the projectile and one electron already promoted to the continuum through electron-electron correlation in the first-order process.
Absorbing-State Phase Transitions On Percolating Lattices, Man Young Lee, Thomas Vojta
Absorbing-State Phase Transitions On Percolating Lattices, Man Young Lee, Thomas Vojta
Physics Faculty Research & Creative Works
We study nonequilibrium phase transitions of reaction-diffusion systems defined on randomly diluted lattices, focusing on the transition across the lattice percolation threshold. To develop a theory for this transition, we combine classical percolation theory with the properties of the supercritical nonequilibrium system on a finite-size cluster. In the case of the contact process, the interplay between geometric criticality due to percolation and dynamical fluctuations of the nonequilibrium system leads to a different universality class. The critical point is characterized by ultraslow activated dynamical scaling and accompanied by strong Griffiths singularities. To confirm the universality of this exotic scaling scenario we …
Binding Two-Loop Vacuum-Polarization Corrections To The Bound-Electron G Factor, Ulrich D. Jentschura
Binding Two-Loop Vacuum-Polarization Corrections To The Bound-Electron G Factor, Ulrich D. Jentschura
Physics Faculty Research & Creative Works
We commence the evaluation of the one- and two-loop binding corrections to the g factor for an electron in a hydrogenlike system of order alpha2(Zalpha)5 and consider diagrams with closed fermion loops. The one-loop vacuum-polarization correction is rederived and confirmed. For the two-loop vacuum-polarization correction, due to a specific gauge-invariant set of diagrams with closed fermion loops, we find a correction deltag=7.442(alpha/pi)2(Zalpha)5. Based on the numerical trend of the coefficients inferred from the gauge-invariant subset, we obtain a numerically large tentative estimate for the complete two-loop binding correction to the g factor (sum of self-energy and vacuum polarization).
Quantitative Rescattering Theory For Laser-Induced High-Energy Plateau Photoelectron Spectra, Zhangjin Chen, Anh-Thu Le, Toru Morishita, C. D. Lin
Quantitative Rescattering Theory For Laser-Induced High-Energy Plateau Photoelectron Spectra, Zhangjin Chen, Anh-Thu Le, Toru Morishita, C. D. Lin
Physics Faculty Research & Creative Works
A comprehensive quantitative rescattering (QRS) theory for describing the production of high-energy photoelectrons generated by intense laser pulses is presented. According to the QRS, the momentum distributions of these electrons can be expressed as the product of a returning electron wave packet with the elastic differential cross sections (DCS) between free electrons with the target ion. We show that the returning electron wave packets are determined mostly by the lasers only and can be obtained from the strong field approximation. The validity of the QRS model is carefully examined by checking against accurate results from the solution of the time-dependent …
Magnetic Ordering In The Spinel Compound Li[Mn₂₋ₓlix]O₄(X=0, 0.04), John Gaddy, Jagat Lamsal, Marcus Petrovic, Wouter Montfrooij, Alexander Schmets, Thomas Vojta
Magnetic Ordering In The Spinel Compound Li[Mn₂₋ₓlix]O₄(X=0, 0.04), John Gaddy, Jagat Lamsal, Marcus Petrovic, Wouter Montfrooij, Alexander Schmets, Thomas Vojta
Physics Faculty Research & Creative Works
The two B-site ions Mn3+ and Mn4+ in the stoichiometric spinel structure LiMn2O4 form a complex, columnar ordered pattern below the charge-ordering transition at room temperature. On further cooling to below 66 K, the system develops long-range antiferromagnetic order. In contrast, whereas lithium-substituted Li[Mn2−xLix]O4 also undergoes a charge-ordering transition around room temperature, it only displays frozen in short-range magnetic order below ~25-30 K. We investigate to what extent the columnar charge-order pattern observed in LiMn2O4 can account for the measured magnetic ordering patterns in both the pure and Li-substituted (x=0.04) compounds. We conclude that eightfold rings of Mn4+ ions form …
All-Sky Ligo Search For Periodic Gravitational Waves In The Early Fifth-Science-Run Data, Benjamin P. Abbott, Marco Cavaglia, For Full List Of Authors, See Publisher's Website.
All-Sky Ligo Search For Periodic Gravitational Waves In The Early Fifth-Science-Run Data, Benjamin P. Abbott, Marco Cavaglia, For Full List Of Authors, See Publisher's Website.
Physics Faculty Research & Creative Works
We report on an all-sky search with the LIGO detectors for periodic gravitational waves in the frequency range 50-1100Hz and with the frequency's time derivative in the range -5x10-9-0Hzs-1. Data from the first eight months of the fifth LIGO science run (S5) have been used in this search, which is based on a semicoherent method (PowerFlux) of summing strain power. Observing no evidence of periodic gravitational radiation, we report 95% confidence-level upper limits on radiation emitted by any unknown isolated rotating neutron stars within the search range. Strain limits below 10-24 are obtained over a …
Accurate Retrieval Of Target Structures And Laser Parameters Of Few-Cycle Pulses From Photoelectron Momentum Spectra, Samuel Micheau, Zhangjin Chen, Anh-Thu Le, J. Rauschenberger, M. F. Kling, C. D. Lin
Accurate Retrieval Of Target Structures And Laser Parameters Of Few-Cycle Pulses From Photoelectron Momentum Spectra, Samuel Micheau, Zhangjin Chen, Anh-Thu Le, J. Rauschenberger, M. F. Kling, C. D. Lin
Physics Faculty Research & Creative Works
We illustrate a new method of analyzing three-dimensional momentum images of high-energy photoelectrons generated by intense phase-stabilized few-cycle laser pulses. Using photoelectron momentum spectra that were obtained by velocity-map imaging of above-threshold ionization of xenon and argon targets, we show that the absolute carrier-envelope phase, the laser peak intensity, and pulse duration can be accurately determined simultaneously (with an error of a few percent). We also show that the target structure, in the form of electron-target ion elastic differential cross sections, can be retrieved over a range of energies. The latter offers the promise of using laser-generated electron spectra for …
Virtual Resonant States In Two-Photon Decay Processes: Lower-Order Terms, Subtractions, And Physical Interpretations, Ulrich D. Jentschura
Virtual Resonant States In Two-Photon Decay Processes: Lower-Order Terms, Subtractions, And Physical Interpretations, Ulrich D. Jentschura
Physics Faculty Research & Creative Works
We investigate the two-photon decay rate of a highly excited atomic state which can decay to bound states of lower energy via cascade processes. We show that a naïve treatment of the process, based on the introduction of phenomenological decay rates for the intermediate, resonant states, leads to lower-order terms which need to be subtracted in order to obtain the coherent two-photon correction to the decay rate. The sum of the lower-order terms is exactly equal to the one-photon decay rate of the initial state, provided the naïve two-photon decay rates are summed over all available two-photon channels. A quantum …
Recursive Algorithm For Arrays Of Generalized Bessel Functions: Numerical Access To Dirac-Volkov Solutions, Erik Lötstedt, Ulrich D. Jentschura
Recursive Algorithm For Arrays Of Generalized Bessel Functions: Numerical Access To Dirac-Volkov Solutions, Erik Lötstedt, Ulrich D. Jentschura
Physics Faculty Research & Creative Works
In the relativistic and the nonrelativistic theoretical treatment of moderate and high-power laser-matter interaction, the generalized Bessel function occurs naturally when a Schrödinger-Volkov and Dirac-Volkov solution is expanded into plane waves. For the evaluation of cross sections of quantum electrodynamic processes in a linearly polarized laser field, it is often necessary to evaluate large arrays of generalized Bessel functions, of arbitrary index but with fixed arguments. We show that the generalized Bessel function can be evaluated, in a numerically stable way, by utilizing a recurrence relation and a normalization condition only, without having to compute any initial value. We demonstrate …
Isotope Shifts In Dielectronic Recombination: From Stable To In-Flight-Produced Nuclei, Carsten Brandau, S. Kozhedub, Alfred K. Muller, Dietrich Bernhardt, Stefan Bohm, Fritz J. Bosch, Daniel Boutin, Fred John Currell, Christina Dimopoulou, Bernhard Franzke, Alexandre Gumberidze, Zoltan Harman, Ulrich D. Jentschura, Christoph H. Keitel, Heinz Jurgen Kluge, S. Kozhedub, Reiner Krucken, Yu A. Litvinov, Fritz Nolden, Brian E. O'Rourke, Regina Reuschl, Stefan Schippers, Vladimir M. Shabaev, Uwe Spillmann, Zbigniew Stachura
Isotope Shifts In Dielectronic Recombination: From Stable To In-Flight-Produced Nuclei, Carsten Brandau, S. Kozhedub, Alfred K. Muller, Dietrich Bernhardt, Stefan Bohm, Fritz J. Bosch, Daniel Boutin, Fred John Currell, Christina Dimopoulou, Bernhard Franzke, Alexandre Gumberidze, Zoltan Harman, Ulrich D. Jentschura, Christoph H. Keitel, Heinz Jurgen Kluge, S. Kozhedub, Reiner Krucken, Yu A. Litvinov, Fritz Nolden, Brian E. O'Rourke, Regina Reuschl, Stefan Schippers, Vladimir M. Shabaev, Uwe Spillmann, Zbigniew Stachura
Physics Faculty Research & Creative Works
The study of isotope shifts and hyperfine effects in dielectronic recombination (DR) resonance spectra strikes a conceptually new path for investigations of nuclear properties such as charge radius, spin, magnetic moment of nuclei or lifetimes of long-lived excited nuclear states. A series of DR experiments with heavy three-electron ions (Li-like) was performed at the heavy-ion storage ring ESR of the GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany. In a pilot experiment the two stable isotopes A=142 and A=150 of neodymium ANd57+ were investigated. From the displacement of DR resonances the isotope shifts δE142,150(2s - 2Pl/2) …
Quantitative Rescattering Theory For Nonsequential Double Ionization Of Atoms By Intense Laser Pulses, Samuel Micheau, Zhangjin Chen, Anh-Thu Le, C. D. Lin
Quantitative Rescattering Theory For Nonsequential Double Ionization Of Atoms By Intense Laser Pulses, Samuel Micheau, Zhangjin Chen, Anh-Thu Le, C. D. Lin
Physics Faculty Research & Creative Works
Laser-induced electron recollisions are fundamental to many strong field phenomena in atoms and molecules. Using the recently developed quantitative rescattering theory, we demonstrate that the nonsequential double ionization (NSDI) of atoms by lasers can be obtained quantitatively in terms of inelastic collisions of the target ions with the free returning electrons where the latter are explicitly given by a spectrum-characterized wave packet. Using argon atoms as target, we calculated the NSDI yield including contributions from direct (e,2e) electron-impact ionization and electron-impact excitation accompanied by subsequent field ionization. We further investigate the dependence of total NSDI on the carrier-envelope phase of …
Kinetic Energy Release Distributions For C⁺₂ Emission From Multiply Charged C₆₀ And C₇₀ Fullerenes, Henrik Cederquist, Nicole Haag, Zoltan Berenyi, Peter Reinhed, Daniel Fischer, M. Gudmundsson, Birgitta W. Johansson, Torsten Schmidt, Henning Zettergren
Kinetic Energy Release Distributions For C⁺₂ Emission From Multiply Charged C₆₀ And C₇₀ Fullerenes, Henrik Cederquist, Nicole Haag, Zoltan Berenyi, Peter Reinhed, Daniel Fischer, M. Gudmundsson, Birgitta W. Johansson, Torsten Schmidt, Henning Zettergren
Physics Faculty Research & Creative Works
We present asystematic study of experimental kinetic energy release distributions for the asymmetric fission processes Cq+60 C(iq-1<)+70+ C+2 and C q+70 C(q-1)+60+ C+ 2 for mother ions incharge states q 4-8 produced incollisions with slow highly charged ions. Somewhat to our surprise, we find that the KERD for asymmetric fission from Cq+60 are considerably wider and have larger most likely values than the Cq+70 distributions inthe corresponding charge states when q > 4.
Electron Angular Distributions In He Single Ionization Impact By H₂⁺ Ions At 1 Mev, Shaofeng Zhang, J. Suske, Daniel Fischer, K. U. Kuehnel, Siegbert Hagmann, Alexander B. Voitkiv, B. Najjari, Achim Krauss, Robert Moshammer, Joachim Hermann Ullrich, Xinwen Ma
Electron Angular Distributions In He Single Ionization Impact By H₂⁺ Ions At 1 Mev, Shaofeng Zhang, J. Suske, Daniel Fischer, K. U. Kuehnel, Siegbert Hagmann, Alexander B. Voitkiv, B. Najjari, Achim Krauss, Robert Moshammer, Joachim Hermann Ullrich, Xinwen Ma
Physics Faculty Research & Creative Works
For the first time we investigated in a kinematically complete experiment the ionization of helium in collisions with H2+-molecular ions at 1 MeV. Using two separate detectors, the orientation of the projectile H2+-molecular ions was determined at the instance of the collision. The electron angular distribution was measured by a "Reaction Microscope". The observed structures are found in agreement with theoretical calculations, indicating that the ionized electron of He shows a slight preferential emission direction parallel to the molecular axis.
Sequential And Direct Two-Photon Double Ionization Of D₂ At Flash, Y. H. Jiang, Artem Rudenko, Kai Uwe Kuhnel, Th. Ergler, S. Ludemann, Karl Zrost, Daniel Fischer, J. Perez-Torres, E. Plesiat, F. Martin, L. Foucar, J. Titze, Markus S. Schoffler, Reinhard Dorner, J. L. Sanz-Vicario, S. Dusterer, R. Treusch, Claus Dieter Schroter, Robert Moshammer, Joachim Hermann Ullrich
Sequential And Direct Two-Photon Double Ionization Of D₂ At Flash, Y. H. Jiang, Artem Rudenko, Kai Uwe Kuhnel, Th. Ergler, S. Ludemann, Karl Zrost, Daniel Fischer, J. Perez-Torres, E. Plesiat, F. Martin, L. Foucar, J. Titze, Markus S. Schoffler, Reinhard Dorner, J. L. Sanz-Vicario, S. Dusterer, R. Treusch, Claus Dieter Schroter, Robert Moshammer, Joachim Hermann Ullrich
Physics Faculty Research & Creative Works
Sequential and direct two-photon double ionization (DI) of D2 molecule is studied experimentally and theoretically at a photon energy of 38.8 eV. Experimental and theoretical kinetic energy releases of D++D+fragments, consisting of the contributions of sequential DI via the D2+(1sσg) state and direct DI via a virtual state, agree well with each other.
Coulomb-Field-Induced Conversion Of A High-Energy Photon Into A Pair Assisted By A Counterpropagating Laser Beam, Erik Lotstedt, Ulrich D. Jentschura, Christoph H. Keitel
Coulomb-Field-Induced Conversion Of A High-Energy Photon Into A Pair Assisted By A Counterpropagating Laser Beam, Erik Lotstedt, Ulrich D. Jentschura, Christoph H. Keitel
Physics Faculty Research & Creative Works
The laser-induced modification of a fundamental process of quantum electrodynamics, the conversion of a high-energy gamma photon in the Coulomb field of a nucleus into an electron-positron pair, is studied theoretically. Although the employed formalism allows for the general case where the gamma photon and laser photons cross at an arbitrary angle, we here focus on a theoretically interesting and numerically challenging setup, where the laser beam and gamma photon counterpropagate and impinge on a nucleus at rest. For a peak laser field smaller than the critical Schwinger field and gamma photon energy larger than the field-free threshold, the total …
The Search For Quantum Critical Scaling In A Classical System, Jagat Lamsal, John Gaddy, Marcus Petrovic, Wouter Montfrooij, Thomas Vojta
The Search For Quantum Critical Scaling In A Classical System, Jagat Lamsal, John Gaddy, Marcus Petrovic, Wouter Montfrooij, Thomas Vojta
Physics Faculty Research & Creative Works
Order-disorder phase transitions in magnetic metals that occur at zero temperature have been studied in great detail. Theorists have advanced scenarios for these quantum critical systems in which the unusual response can be seen to evolve from a competition between ordering and disordering tendencies, driven by quantum fluctuations. Unfortunately, there is a potential disconnect between the real systems that are being studied experimentally, and the idealized systems that theoretical scenarios are based upon. Here we discuss how disorder introduces a change in morphology from a three-dimensional system to a collection of magnetic clusters, and we present neutron scattering data on …
Unified Treatment Of Even And Odd Anharmonic Oscillators Of Arbitrary Degree, Ulrich D. Jentschura, Andrey Surzhykov, Jean Zinn-Justin
Unified Treatment Of Even And Odd Anharmonic Oscillators Of Arbitrary Degree, Ulrich D. Jentschura, Andrey Surzhykov, Jean Zinn-Justin
Physics Faculty Research & Creative Works
We present a unified treatment, including higher-order corrections, of anharmonic oscillators of arbitrary even and odd degree. Our approach is based on a dispersion relation which takes advantage of the [script P][script T] symmetry of odd potentials for imaginary coupling parameter, and of generalized quantization conditions which take into account instanton contributions. We find a number of explicit new results, including the general behavior of large-order perturbation theory for arbitrary levels of odd anharmonic oscillators, and subleading corrections to the decay width of excited states for odd potentials, which are numerically significant.
Emission Of Low-Energy Photons By Electrons At Electron-Positron And Electron-Ion Colliders With Dense Bunches, Ulrich D. Jentschura, G. L. Kotkin, V. G. Serbo
Emission Of Low-Energy Photons By Electrons At Electron-Positron And Electron-Ion Colliders With Dense Bunches, Ulrich D. Jentschura, G. L. Kotkin, V. G. Serbo
Physics Faculty Research & Creative Works
Usually, the emission of low-energy photons in electron-positron (or electron-ion) bunch collisions is calculated with the same approach as for synchrotron radiation (beamstrahlung). However, for soft photons (Eγ
Infinite-Randomness Critical Point In The Two-Dimensional Disordered Contact Process, Thomas Vojta, A. Farquhar, J. Mast
Infinite-Randomness Critical Point In The Two-Dimensional Disordered Contact Process, Thomas Vojta, A. Farquhar, J. Mast
Physics Faculty Research & Creative Works
We study the nonequilibrium phase transition in the two-dimensional contact process on a randomly diluted lattice by means of large-scale Monte Carlo simulations for times up to 1010 and system sizes up to 8000×8000 sites. Our data provide strong evidence for the transition being controlled by an exotic infinite-randomness critical point with activated (exponential) dynamical scaling. We calculate the critical exponents of the transition and find them to be universal, i.e., independent of disorder strength. The Griffiths region between the clean and the dirty critical points exhibits power-law dynamical scaling with continuously varying exponents. We discuss the generality of our …
Extensions Of Effective-Medium Theory Of Transport In Disordered Systems, V. M. Kenkre, Z. Kalay, Paul Ernest Parris
Extensions Of Effective-Medium Theory Of Transport In Disordered Systems, V. M. Kenkre, Z. Kalay, Paul Ernest Parris
Physics Faculty Research & Creative Works
The effective-medium theory of transport in disordered systems, whose basis is the replacement of spatial disorder by temporal memory, is extended in several practical directions. Restricting attention to a one-dimensional system with bond disorder for specificity, a transformation procedure is developed to deduce explicit expressions for the memory functions from given distribution functions characterizing the system disorder. It is shown how to use the memory functions in the Laplace domain forms in which they first appear, and in the time domain forms which are obtained via numerical inversion algorithms, to address time evolution of the system beyond the asymptotic domain …
Infinite-Randomness Quantum Critical Points Induced By Dissipation, Thomas Vojta, Chetan Kotabage, Jose A. Hoyos
Infinite-Randomness Quantum Critical Points Induced By Dissipation, Thomas Vojta, Chetan Kotabage, Jose A. Hoyos
Physics Faculty Research & Creative Works
We develop a strong-disorder renormalization group to study quantum phase transitions with continuous O(N) symmetry order parameters under the influence of both quenched disorder and dissipation. For Ohmic dissipation, as realized in Hertz's theory of the itinerant antiferromagnetic transition or in the superconductor-metal transition in nanowires, we find the transition to be governed by an exotic infinite-randomness fixed point in the same universality class as the (dissipationless) random transverse-field Ising model. We determine the critical behavior and calculate key observables at the transition and in the associated quantum Griffiths phase. We also briefly discuss the cases of super-Ohmic and sub-Ohmic …