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Physics Faculty Research & Creative Works

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Articles 871 - 900 of 1762

Full-Text Articles in Physical Sciences and Mathematics

(E,2e) Measurements On Xenon: Reexamination Of The Fine-Structure Effect, Radmila Panajotovic, Julian C A Lower, Erich Weigold, A. Prideaux, Don H. Madison May 2006

(E,2e) Measurements On Xenon: Reexamination Of The Fine-Structure Effect, Radmila Panajotovic, Julian C A Lower, Erich Weigold, A. Prideaux, Don H. Madison

Physics Faculty Research & Creative Works

The process of electron scattering from heavy target atoms is of considerable interest due to the enhanced role of relativistic effects and distortion of the electron trajectories resulting from the large value of nuclear charge. Here we present (e,2e) ionization measurements and distorted-wave Born approximation calculations for the scattering of spin-polarized electrons from xenon atoms in which the fine-structure levels of the residual ion are resolved. Comparison of measurements performed using a high-sensitivity toroidal analyzer spectrometer with the predictions of sophisticated calculations provide an improved understanding of the ionization dynamics of heavy target atoms and the treatment of electron exchange …

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Benchmarking High-Field Few-Electron Correlation And Qed Contributions In Hg⁷⁵⁺ To Hg⁷⁸⁺ Ions. I. Experiment, Antonio J. Gonzalez, Jose R. Crespo Lopez-Urrutia, Jean Pierre Braun, Gunter Brenner, Hjalmar Bruhns, Alain Lapierre, Vladimir Sergeyevich Mironov, R. Soria Orts, Hiroyuki Tawara, Michael Trinczek, Joachim Hermann Ullrich, Anton N. Artemyev, Zoltan Harman, Ulrich D. Jentschura, Christoph H. Keitel, James H. Scofield, I. I. Tupitsyn May 2006

Benchmarking High-Field Few-Electron Correlation And Qed Contributions In Hg⁷⁵⁺ To Hg⁷⁸⁺ Ions. I. Experiment, Antonio J. Gonzalez, Jose R. Crespo Lopez-Urrutia, Jean Pierre Braun, Gunter Brenner, Hjalmar Bruhns, Alain Lapierre, Vladimir Sergeyevich Mironov, R. Soria Orts, Hiroyuki Tawara, Michael Trinczek, Joachim Hermann Ullrich, Anton N. Artemyev, Zoltan Harman, Ulrich D. Jentschura, Christoph H. Keitel, James H. Scofield, I. I. Tupitsyn

Physics Faculty Research & Creative Works

The photorecombination of highly charged few-electron mercury ions Hg75+ to Hg78+ has been explored with the Heidelberg electron beam ion trap. By monitoring the emitted x rays (65-76 keV) and scanning the electron beam energy (45-54 keV) over the KLL dielectronic recombination (DR) region, the energies of state-selected DR resonances were determined to within ±4 eV (relative) and ±14 eV (absolute). At this level of experimental accuracy, it becomes possible to make a detailed comparison to various theoretical approaches and methods, all of which include quantum electrodynamic (QED) effects and finite nuclear size contributions (for a 1s electron, …

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Two-Photon Excitation Dynamics In Bound Two-Body Coulomb Systems Including Ac Stark Shift And Ionization, Martin K. Haas, Ulrich D. Jentschura, Christoph H. Keitel, Nikolai N. Kolachevsky, Maximilian Herrmann, Peter Fendel, Marc P. Fischer, Th H. Udem, Ronald Holzwarth, Theodor Wolfgang Hansch, Marlan O. Scully, Girish S. Agarwal May 2006

Two-Photon Excitation Dynamics In Bound Two-Body Coulomb Systems Including Ac Stark Shift And Ionization, Martin K. Haas, Ulrich D. Jentschura, Christoph H. Keitel, Nikolai N. Kolachevsky, Maximilian Herrmann, Peter Fendel, Marc P. Fischer, Th H. Udem, Ronald Holzwarth, Theodor Wolfgang Hansch, Marlan O. Scully, Girish S. Agarwal

Physics Faculty Research & Creative Works

One of the dominant systematic effects that shift resonance lines in high-precision measurements of two-photon transitions is the dynamic (ac) Stark shift. For suitable laser frequencies, the ac Stark shift acquires an imaginary part which corresponds to the rate of resonant one-photon ionization of electrons into a continuum state. At the current level of spectroscopic accuracy, the underlying time-dependent quantum dynamics governing the atomic two-photon excitation process must be well understood, and related considerations are the subject of the present paper. In order to illustrate the basic mechanisms in the transient regime, we investigate an analytically solvable model scenario for …

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Benchmarking High-Field Few-Electron Correlation And Qed Contributions In Hg⁷⁵⁺ To Hg⁷⁸⁺ Ions. Ii. Theory, Zoltan Harman, I. I. Tupitsyn, Anton N. Artemyev, Ulrich D. Jentschura, Christoph H. Keitel, Jose R. Crespo Lopez-Urrutia, Antonio J. Gonzalez, Hiroyuki Tawara, Joachim Hermann Ullrich May 2006

Benchmarking High-Field Few-Electron Correlation And Qed Contributions In Hg⁷⁵⁺ To Hg⁷⁸⁺ Ions. Ii. Theory, Zoltan Harman, I. I. Tupitsyn, Anton N. Artemyev, Ulrich D. Jentschura, Christoph H. Keitel, Jose R. Crespo Lopez-Urrutia, Antonio J. Gonzalez, Hiroyuki Tawara, Joachim Hermann Ullrich

Physics Faculty Research & Creative Works

Theoretical resonance energies for KLL dielectronic recombination into He-, Li-, Be-, and B-like Hg ions are calculated by various means and discussed in detail. We apply the multiconfiguration Dirac-Fock and the configuration interaction Dirac-Fock-Sturmian methods, and quantum electrodynamic many-body theory. The different contributions such as relativistic electron interaction, quantum electrodynamic contributions, and finite nuclear size and mass corrections are calculated and their respective theoretical uncertainties are estimated. Our final results are compared to experimental data from the preceding paper. The comparison of theoretical values with the experimental energies shows a good overall agreement for most transitions and illustrates the significance …

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Evidence Of Two-Center Interference In High-Order Harmonic Generation From Co₂, Anh-Thu Le, Xiao-Min Tong, C. D. Lin Apr 2006

Evidence Of Two-Center Interference In High-Order Harmonic Generation From Co₂, Anh-Thu Le, Xiao-Min Tong, C. D. Lin

Physics Faculty Research & Creative Works

Two recent pump-probe experiments on the high-order harmonic generation (HHG) from partially aligned CO₂ molecules have shown that the HHG yields versus the ionization rates as functions of the pump-probe delay time exhibit inverted modulation. The inversion has been attributed to the quantum interference in the recombination process from the two oxygen centers. Using the Lewenstein model to calculate HHG from fixed CO₂ molecules and taking into account the partial alignment of the molecules versus the time delay, we interpret that the inversion is due to the degree of overlap between the partially aligned molecules and the angular dependence of …

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Modeling Study Of The Dip-Hump Feature In Bi₂ Sr₂ Cacu₂ O8+Δ Tunneling Spectroscopy, Pierom Romano, Lutfi Ozyuzer, Zikri M. Yusof, Cihan Kurter, John F. Zasadzinski Mar 2006

Modeling Study Of The Dip-Hump Feature In Bi₂ Sr₂ Cacu₂ O8+Δ Tunneling Spectroscopy, Pierom Romano, Lutfi Ozyuzer, Zikri M. Yusof, Cihan Kurter, John F. Zasadzinski

Physics Faculty Research & Creative Works

The tunneling spectra of high-temperature superconductors on Bi2 Sr2 CaCu2 O8+δ (Bi-2212) reproducibly show a high-bias structure in the form of a dip-hump at voltages higher than the gap voltage. Of central concern is whether this feature originates from the normal state background or is intrinsic to the superconducting mechanism. We address this issue by generating a set of model conductance curves-a "normal state" conductance that takes into account effects such as the band structure and a possible pseudogap, and a pure superconducting state conductance. When combined, the result shows that the dip-hump feature present in …

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Radiative Electron Capture Into High- Z Few-Electron Ions: Alignment Of The Excited Ionic States, Andrey S. Surzhykov, Ulrich D. Jentschura, Th H. Stohlker, Stephan Fritzsche Mar 2006

Radiative Electron Capture Into High- Z Few-Electron Ions: Alignment Of The Excited Ionic States, Andrey S. Surzhykov, Ulrich D. Jentschura, Th H. Stohlker, Stephan Fritzsche

Physics Faculty Research & Creative Works

We lay out a unified formalism for the description of radiative electron capture into excited states of heavy, few-electron ions and their subsequent decay, including a full account of many-electron effects and higher-order multipoles of the radiation field. In particular, the density-matrix theory is applied to explore the magnetic sublevel population of the residual ions, as described in terms of alignment parameters. For the electron capture into the initially hydrogenlike U91+ and lithiumlike U89+ uranium projectiles, the alignment parameters are calculated, within the multiconfiguration Dirac-Fock approach, as a function of the collision energy and for different ionic states. …

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X-Ray Emission Cross Sections Following Charge Exchange By Multiply Charged Ions Of Astrophysical Interest, Sebastian Otranto, Ronald E. Olson, P. Beiersdorfer Feb 2006

X-Ray Emission Cross Sections Following Charge Exchange By Multiply Charged Ions Of Astrophysical Interest, Sebastian Otranto, Ronald E. Olson, P. Beiersdorfer

Physics Faculty Research & Creative Works

State selective nl-electron capture cross sections are presented for highly charged ions with Z=6-10 colliding with atoms and molecules. The energy range investigated was from 1 eV/amu(v=0.006 a.u.)to 100 keV/amu(v=2.0 a.u.). The energy dependence of the l-level populations is investigated. The K shell x-ray emission cross sections are determined by using the calculated state-selective electron capture results as input and then applying hydrogenic branching and cascading values for the photon emission. A major shift in the line emission from being almost solely Lyman-alpha transitions at the highest collisions energies to strong high-n to 1s transitions at the lowest energies is …

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Erratum: Black Hole Particle Emission In Higher-Dimensional Spacetimes (Physical Review Letters (2006) 96 (071301)), Vitor Cardoso, Marco Cavaglia, Leonardo Gualtieri Feb 2006

Erratum: Black Hole Particle Emission In Higher-Dimensional Spacetimes (Physical Review Letters (2006) 96 (071301)), Vitor Cardoso, Marco Cavaglia, Leonardo Gualtieri

Physics Faculty Research & Creative Works

No abstract provided.

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Black Hole Particle Emission In Higher-Dimensional Spacetimes, Vitor Cardoso, Marco Cavaglia, Leonardo Gualtieri Feb 2006

Black Hole Particle Emission In Higher-Dimensional Spacetimes, Vitor Cardoso, Marco Cavaglia, Leonardo Gualtieri

Physics Faculty Research & Creative Works

In models with extra dimensions, a black hole evaporates both in the bulk and on the visible brane, where standard model fields live. The exact emissivities of each particle species are needed to determine how the black hole decay proceeds. We compute and discuss the absorption cross sections, the relative emissivities, and the total power output of all known fields in the evaporation phase. Graviton emissivity is highly enhanced as the spacetime dimensionality increases. Therefore, a black hole loses a significant fraction of its mass in the bulk. This result has important consequences for the phenomenology of black holes in …

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Simulations Of Black Hole Air Showers In Cosmic Ray Detectors, Eun-Joo Ahn, Marco Cavaglia Feb 2006

Simulations Of Black Hole Air Showers In Cosmic Ray Detectors, Eun-Joo Ahn, Marco Cavaglia

Physics Faculty Research & Creative Works

We present a comprehensive study of TeV black hole events in Earth's atmosphere originated by cosmic rays of very high energy. An advanced fortran Monte Carlo code is developed and used to simulate black hole extensive air showers from ultrahigh-energy neutrino-nucleon interactions. We investigate the characteristics of these events, compare the black hole air showers to standard model air showers, and test different theoretical and phenomenological models of black hole formation and evolution. The main features of black hole air showers are found to be independent of the model considered. No significant differences between models are likely to be observed …

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Ƒ-Electron Correlations In Nonmagnetic Ce Studied By Means Of Spin-Resolved Resonant Photoemission, S. W. Yu, Takashi Komesu, B. W. Chung, Simon A. Morton, James G. Tobin, George Daniel Waddill Feb 2006

Ƒ-Electron Correlations In Nonmagnetic Ce Studied By Means Of Spin-Resolved Resonant Photoemission, S. W. Yu, Takashi Komesu, B. W. Chung, Simon A. Morton, James G. Tobin, George Daniel Waddill

Physics Faculty Research & Creative Works

We have studied the spin-spin coupling between two f electrons of nonmagnetic Ce by means of spin-resolved resonant photoemission using circularly polarized synchrotron radiation. The two f electrons participating in the 3d5/2-->4f resonance process are coupled in a singlet while the coupling is veiled in the 3d3/2-->4f process due to an additional Coster-Kronig decay channel. The identical singlet coupling is observed in the 4d-->4f resonance process. Based on the Ce measurements, it is argued that spin-resolved resonant photoemission is one approach to study the correlation effects, particularly in the form of spin, in the rare earths.

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Kinetic Correlation In Photo-Double-Ionization Processes: The He-Isoelectronic Sequence, Sebastian Otranto, C. R. Garibotti Jan 2006

Kinetic Correlation In Photo-Double-Ionization Processes: The He-Isoelectronic Sequence, Sebastian Otranto, C. R. Garibotti

Physics Faculty Research & Creative Works

Analytical models proposed to represent the two-electron continuum are revisited. Main results obtained with these models are summarized. Recent studies of the photo-double-ionization (PDI) of the He-isoelectronic sequence by means of the recently introduced SC3 model are shown and compared with the results predicted by classical and semi-classical Wannier approaches. By fitting the triply differential cross sections (TDCSs) with the usual dipolar Gaussian form we find that the width has a power dependence on excess energy with exponent 0.25 in the near threshold region and departs from this law with increasing energy

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Self-Optimization Of Optical Confinement In An Ultraviolet Photonic Crystal Slab Laser, Alexey Yamilov, X. Wu, X. Liu, Hui Cao, Robert P. H. Chang Jan 2006

Self-Optimization Of Optical Confinement In An Ultraviolet Photonic Crystal Slab Laser, Alexey Yamilov, X. Wu, X. Liu, Hui Cao, Robert P. H. Chang

Physics Faculty Research & Creative Works

We studied numerically and experimentally the effects of structural disorder on the performance of ultraviolet photonic crystal slab lasers. Optical gain selectively amplifies the high-quality modes of the passive system. For these modes, the in-plane and out-of-plane leakage rates may be automatically balanced in the presence of disorder. The spontaneous optimization of in-plane and out-of-plane confinement of light in a photonic crystal slab may lead to a reduction of the lasing threshold.

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Theoretical Treatment Of Electron-Impact Ionization Of Molecules, Junfang Gao, Jerry Peacher, Don H. Madison Jan 2006

Theoretical Treatment Of Electron-Impact Ionization Of Molecules, Junfang Gao, Jerry Peacher, Don H. Madison

Physics Faculty Research & Creative Works

There is currently no reliable theory for calculating the fully differential cross section (FDCS) for low energy electron-impact ionization of molecules. All of the existing experimental FDCS data represent averages over all molecular orientations and this can be an important theoretical complication for calculations that are computer intensive. We have found that using an averaged molecular orbital is an accurate approximation for ionization of ground states. In this paper, we will describe the approximation, discuss its expected range of validity and show some FDCS results using the approximation for ionization of H2 and N2

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Adiabatic-Nonadiabatic Transition In The Diffusive Hamiltonian Dynamics Of A Classical Holstein Polaron, Alex A. Silvius, Paul Ernest Parris, Stephan De Bièvre Jan 2006

Adiabatic-Nonadiabatic Transition In The Diffusive Hamiltonian Dynamics Of A Classical Holstein Polaron, Alex A. Silvius, Paul Ernest Parris, Stephan De Bièvre

Physics Faculty Research & Creative Works

We study the Hamiltonian dynamics of a free particle injected onto a chain containing a periodic array of harmonic oscillators in thermal equilibrium. The particle interacts locally with each oscillator, with an interaction that is linear in the oscillator coordinate and independent of the particle's position when it is within a finite interaction range. At long times the particle exhibits diffusive motion, with an ensemble averaged mean-squared displacement that is linear in time. The diffusion constant at high temperatures follows a power law D~T 5/2 for all parameter values studied. At low temperatures particle transport changes to a hopping process …

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Unexpected Higher-Order Effects In Charged Particle Impact Ionization At High Energies, M. Foster, Jerry Peacher, Michael Schulz, Don H. Madison, Zhangjin Chen, H. R. J. Walters Jan 2006

Unexpected Higher-Order Effects In Charged Particle Impact Ionization At High Energies, M. Foster, Jerry Peacher, Michael Schulz, Don H. Madison, Zhangjin Chen, H. R. J. Walters

Physics Faculty Research & Creative Works

Most of the experimental and theoretical studies of electron-impact ionization of atoms, referred to as (e, 2e), have concentrated on the scattering plane. The assumption has been that all the important physical effects will be observable in the scattering plane. However, very recently it has been shown that, for C6+-helium ionization, experiment and theory are in nice agreement in the scattering plane and in very bad agreement out of the scattering plane. This lack of agreement between experiment and theory has been explained in terms of higher-order scattering effects between the projectile and target ion. We have examined electron-impact ionization …

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Percolation Transition And Dissipation In Quantum Ising Magnets, Jose A. Hoyos, Thomas Vojta Jan 2006

Percolation Transition And Dissipation In Quantum Ising Magnets, Jose A. Hoyos, Thomas Vojta

Physics Faculty Research & Creative Works

We study the effects of dissipation on a randomly diluted transverse-field Ising magnet close to the percolation threshold. For weak transverse fields, a percolation quantum phase transition separates a superparamagnetic cluster phase from an inhomogeneously ordered ferromagnetic phase. The properties of this transition are dominated by large frozen and slowly fluctuating percolation clusters. This leads to a discontinuous magnetization-field curve and exotic hysteresis phenomena as well as highly singular behavior of magnetic susceptibility and specific heat. We compare our results to the smeared transition in generic dissipative random quantum Ising magnets. We also discuss the relation to metallic quantum magnets …

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Random Lasing In Weakly Scattering Systems, X. Wu, W. Fang, Alexey Yamilov, A. A. Asatryan, L. C. Botten, Andrey A. Chabanov, Hui Cao Jan 2006

Random Lasing In Weakly Scattering Systems, X. Wu, W. Fang, Alexey Yamilov, A. A. Asatryan, L. C. Botten, Andrey A. Chabanov, Hui Cao

Physics Faculty Research & Creative Works

We present detailed experimental and numerical studies of random lasing in weakly scattering systems. The interference of scattered light, which is weak in the passive systems, is greatly enhanced in the presence of high gain, providing coherent and resonant feedback for lasing. The lasing modes are confined in the vicinity of the pumped volume due to absorption of emitted light outside it. In the ballistic regime where the size of the gain volume is less than the scattering mean free path, lasing oscillation occurs along the direction in which the gain volume is most extended, producing directional laser output. The …

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Ultraviolet Lasing In High-Order Bands Of Three-Dimensional Zno Photonic Crystals, Michael Scharrer, Alexey Yamilov, Xiaohua Wu, Hui Cao, Robert P. H. Chang Jan 2006

Ultraviolet Lasing In High-Order Bands Of Three-Dimensional Zno Photonic Crystals, Michael Scharrer, Alexey Yamilov, Xiaohua Wu, Hui Cao, Robert P. H. Chang

Physics Faculty Research & Creative Works

UV lasing in three-dimensional ZnO photonic crystals is demonstrated at room temperature. The photonic crystals are inverse opals with high refractive index contrast that simultaneously confine light and provide optical gain. Highly directional lasing with tunable wavelength is obtained by optical pumping. Comparison of the experimental results to the calculated band structure shows that lasing occurs in high-order bands with abnormally low group velocity. This demonstrates that the high-order band structure of three-dimensional photonic crystals can be used to effectively confine light and enhance emission. Our findings may also impact other applications of photonic crystal devices. ©2006 American Institute of …

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Experimental And Theoretical (E,2e) Ionization Cross Sections For A Hydrogen Target At 75.3 Ev Incident Energy In A Coplanar Asymmetric Geometry, Junfang Gao, Don H. Madison, Jerry Peacher, Andrew James Murray, Martyn J. Hussey Jan 2006

Experimental And Theoretical (E,2e) Ionization Cross Sections For A Hydrogen Target At 75.3 Ev Incident Energy In A Coplanar Asymmetric Geometry, Junfang Gao, Don H. Madison, Jerry Peacher, Andrew James Murray, Martyn J. Hussey

Physics Faculty Research & Creative Works

Very recently it was shown that the molecular three-body distorted wave (M3DW) approach gives good agreement with the shape of the experimental data for electron-impact ionization of H2 in a coplanar symmetric geometry, providing the incident electrons have an energy of 35 eV or greater. One of the weaknesses of these studies was that only the shape of the cross section could be compared to experiment, since there was no absolute or relative normalization of the data. Here we report a joint experimental/theoretical study of electron-impact ionization of H2 in a coplanar asymmetric geometry where the energy of …

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Ionization Of Atoms With Spin Polarized Electrons, J. Lower, S. Bellm, R. Panajotovic, E. Weigold, A. Prideaux, Z. Stegen, Don H. Madison, Colm T. Whelan, B. Lohmann Jan 2006

Ionization Of Atoms With Spin Polarized Electrons, J. Lower, S. Bellm, R. Panajotovic, E. Weigold, A. Prideaux, Z. Stegen, Don H. Madison, Colm T. Whelan, B. Lohmann

Physics Faculty Research & Creative Works

The most detailed insight into the process of electron impact-induced ionization of atomic species is provided by measurements in which both kinematical and quantum mechanical variables are determined. Here we describe recent (e,2e) experimental and theoretical studies involving the ionization of xenon and argon by spin-polarized electrons in which the fine-structure levels of the ion are energetically resolved. Such investigations shed light on the mechanisms driving the ionization reaction and the role of exchange and relativistic processes.

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Kinematically Complete Experiment On Single Ionization In 75-Kev P+He Collisions, Michael Schulz, Ahmad Hasan, N. V. Maydanyuk, M. Foster, B. Tooke, Don H. Madison Jan 2006

Kinematically Complete Experiment On Single Ionization In 75-Kev P+He Collisions, Michael Schulz, Ahmad Hasan, N. V. Maydanyuk, M. Foster, B. Tooke, Don H. Madison

Physics Faculty Research & Creative Works

We have measured and calculated fully differential single-ionization cross sections for the complete three-dimensional space in 75 keV p+He collisions. Several signatures of the projectile-residual-target-ion interaction, some of which are not observable for fast projectiles and for electron impact, are revealed. Some of these features are qualitatively reproduced by our calculations if this interaction is accounted for. However, overall the agreement between theory and experiment is not very good. Thus, our understanding of effects caused by the projectile-residual-target-ion interaction appears to be rather incomplete.

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Magnetically Mediated Transparent Conductors: In₂O₃ Doped With Mo, Julia E. Medvedeva Jan 2006

Magnetically Mediated Transparent Conductors: In₂O₃ Doped With Mo, Julia E. Medvedeva

Physics Faculty Research & Creative Works

First-principles band structure investigations of the electronic, optical, and magnetic properties of Mo-doped In2O3 reveal the vital role of magnetic interactions in determining both the electrical conductivity and the Burstein-Moss shift which governs optical absorption. We demonstrate the advantages of the transition metal doping which results in smaller effective mass, larger fundamental band gap, and better overall optical transmission in the visible as compared to commercial Sn-doped In2O3. Similar behavior is expected upon doping with other transition metals opening up an avenue for the family of efficient transparent conductors mediated by magnetic interactions.

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Photoionization Broadening Of The 1s-2s Transition In A Beam Of Atomic Hydrogen, Nikolai N. Kolachevsky, Martin K. Haas, Ulrich D. Jentschura, Maximilian Herrmann, Peter Fendel, Marc P. Fischer, Ronald Holzwarth, Th H. Udem, Christoph H. Keitel, Theodor Wolfgang Hansch Jan 2006

Photoionization Broadening Of The 1s-2s Transition In A Beam Of Atomic Hydrogen, Nikolai N. Kolachevsky, Martin K. Haas, Ulrich D. Jentschura, Maximilian Herrmann, Peter Fendel, Marc P. Fischer, Ronald Holzwarth, Th H. Udem, Christoph H. Keitel, Theodor Wolfgang Hansch

Physics Faculty Research & Creative Works

We consider the excitation dynamics of the two-photon 1S - 2S transition in a beam of atomic hydrogen by 243 nm laser radiation. Specifically, we study the impact of ionization damping on the transition line shape, caused by the possibility of ionization of the 2S level by the same laser field. Using a Monte Carlo simulation, we calculate the line shape of the 1S - 2S transition for the experimental geometry used in the two latest absolute frequency measurements [M. Niering, Phys. Rev. Lett. 84, 5496 (2000) and M. Fischer, Phys. Rev. Lett. 92, 230802 (2004)]. The calculated line shift …

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Spin Excitations In Fluctuating Stripe Phases Of Doped Cuprate Superconductors, Matthias Vojta, Thomas Vojta, Ribhu K. Kaul Jan 2006

Spin Excitations In Fluctuating Stripe Phases Of Doped Cuprate Superconductors, Matthias Vojta, Thomas Vojta, Ribhu K. Kaul

Physics Faculty Research & Creative Works

Using a phenomenological lattice model of coupled spin and charge modes, we determine the spin susceptibility in the presence of fluctuating stripe charge order. We assume the charge fluctuations to be slow compared to those of the spins, and combine Monte Carlo simulations for the charge order parameter with exact diagonalization of the spin sector. Our calculations unify the spin dynamics of both static and fluctuating stripe phases and support the notion of a universal spin excitation spectrum in doped cuprate superconductors.

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Theoretical Description Of Two- And Three-Particle Interactions In Single Ionization Of Helium By Ion Impact, M. F. Ciappina, W. R. Cravero, Michael Schulz, R. Moshammer, J. D. Ullrich Jan 2006

Theoretical Description Of Two- And Three-Particle Interactions In Single Ionization Of Helium By Ion Impact, M. F. Ciappina, W. R. Cravero, Michael Schulz, R. Moshammer, J. D. Ullrich

Physics Faculty Research & Creative Works

In this work we calculate doubly differential cross sections (DDCS) for single ionization of helium by highly charged ion impact. We study the importance of two-particle interactions in these processes by considering the cross sections as a function of all two-particle subsystems momenta. Experimental DDCSs were obtained recently from kinematically complete experiments on single ionization of He by 100 MeV/amu C6+ and 3.6 MeV/amu Au24,53+ impact. Furthermore, we evaluated the importance of three-particle interactions by plotting the squared momenta of all three collision fragments simultaneously in a Dalitz plot. Using the first Born and distorted-wave approximations for fully differential cross …

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Effect Of Amplification On Conductance Distribution Of A Disordered Waveguide, Alexey Yamilov, Hui Cao Jan 2006

Effect Of Amplification On Conductance Distribution Of A Disordered Waveguide, Alexey Yamilov, Hui Cao

Physics Faculty Research & Creative Works

Introduction of optical gain in a disordered system results in enhanced fluctuations [F(2)=var(g-tilde)/2] of the dimensionless conductance g-tilde, similar to the effect of Anderson localization in a passive medium. Using numerical simulations we demonstrate that, despite such qualitative similarity, the whole distribution of the conductance of amplifying random media is drastically different from that of a passive system with the same value of F(2).

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Initial-State Correlation Effects In Low-Energy Proton Impact Ionization, M. Foster, Jerry Peacher, Ahmad Hasan, Michael Schulz, Don H. Madison Jan 2006

Initial-State Correlation Effects In Low-Energy Proton Impact Ionization, M. Foster, Jerry Peacher, Ahmad Hasan, Michael Schulz, Don H. Madison

Physics Faculty Research & Creative Works

In this paper, we will report on fully differential cross sections (FDCS) for single ionization of helium by 75 keV proton impact for fixed ejected electron energies and different momentum transfers. These measurements show major discrepancies in the absolute magnitude between experiment and the theoretical, 3DW (three-distorted-wave) model. The 3DW model treats the collision as a three-body process (projectile, ion, ejected electron), and for the scattering plane it has accurately predicted the FDCS for higher energy C6+ impact ionization of helium. The lack of agreement between the 3DW model and experiment for low energy collisions suggests that a three-body …

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Slow Dynamics At The Smeared Phase Transition Of Randomly Layered Magnets, Shellie Huether, Ryan Kinney, Thomas Vojta Jan 2006

Slow Dynamics At The Smeared Phase Transition Of Randomly Layered Magnets, Shellie Huether, Ryan Kinney, Thomas Vojta

Physics Faculty Research & Creative Works

We investigate a model for randomly layered magnets, viz., a three-dimensional Ising model with planar defects. The magnetic phase transition in this system is smeared because static long-range order can develop on isolated rare spatial regions. Here, we report large-scale kinetic Monte Carlo simulations of the dynamical behavior close to the smeared phase transition, which we characterize by the spin (time) autocorrelation function. In the paramagnetic phase, its behavior is dominated by Griffiths effects similar to those in magnets with point defects. In the tail region of the smeared transition the dynamics is even slower: the autocorrelation function decays like …

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