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Full-Text Articles in Physical Sciences and Mathematics

Relativistic And Radiative Corrections To The Mollow Spectrum, Jorg Evers, Ulrich D. Jentschura, Christoph H. Keitel Dec 2004

Relativistic And Radiative Corrections To The Mollow Spectrum, Jorg Evers, Ulrich D. Jentschura, Christoph H. Keitel

Physics Faculty Research & Creative Works

The incoherent inelastic part of the resonance fluorescence spectrum of a laser-driven atom is known as the Mollow spectrum [B. R. Mollow, Phys. Rev. 188, 1969 (1969)]. Starting from this level of description, we discuss theoretical foundations of high-precision spectroscopy using the resonance fluorescence light of strongly laser-driven atoms. Specifically, we evaluate the leading relativistic and radiative corrections to the Mollow spectrum, up to the relative orders of ( Z α )2 and α ( Z α )2 , respectively, and Bloch-Siegert shifts as well as stimulated radiative corrections involving off-resonant virtual states. Complete results are provided for the hydrogen 1 S - 2 ...


Nucleation Rates Of Water And Heavy Water Using Equations Of State, Abdalla Obeidat, Jin-Song Li, Gerald Wilemski Nov 2004

Nucleation Rates Of Water And Heavy Water Using Equations Of State, Abdalla Obeidat, Jin-Song Li, Gerald Wilemski

Physics Faculty Research & Creative Works

The original formula of Gibbs for the reversible work of critical nucleus formation is evaluated in three approximate ways for ordinary and heavy water. The least approximate way employs an equation of state to evaluate the pressure difference between the new and old phases. This form of the theory yields a temperature dependence for the nucleation rate close to that observed experimentally. This is a substantial improvement over the most commonly used (and most approximate) form of classical theory.©2004 American Institute of Physics.


Two-Loop Bethe Logarithms For Higher Excited S Levels, Ulrich D. Jentschura Nov 2004

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

Physics Faculty Research & Creative Works

Processes mediated by two virtual low-energy photons contribute quite significantly to the energy of hydrogenic S states. The corresponding level shift is of the order of ( α / π )2 ( Z α )6 mec2 and may be ascribed to a two-loop generalization of the Bethe logarithm. For 1 S and 2 S states, the correction has recently been evaluated by Pachucki and Jentschura [Phys. Rev. Lett. 91, 113005 (2003)]. Here, we generalize the approach to higher excited S states, which in contrast to the 1 S and 2 S states can decay to P states via the electric-dipole ...


Nucleation Near The Spinodal: Limitations Of Mean Field Density Functional Theory, Gerald Wilemski, Jin-Song Li Oct 2004

Nucleation Near The Spinodal: Limitations Of Mean Field Density Functional Theory, Gerald Wilemski, Jin-Song Li

Physics Faculty Research & Creative Works

We investigate the diverging size of the critical nucleus near the spinodal using the gradient theory ~GT! of van der Waals and Cahn and Hilliard and mean field density functional theory ~MFDFT!. As is well known, GT predicts that at the spinodal the free energy barrier to nucleation vanishes while the radius of the critical fluctuation diverges. We show numerically that the scaling behavior found by Cahn and Hilliard for these quantities holds quantitatively for both GT and MFDFT. We also show that the excess number of molecules Dg satisfies Cahn-Hilliard scaling near the spinodal and is consistent with the ...


Fully Differential Three-Dimensional Angular Distributions Of Electrons Ionized In Ion-Atom Collisions, Michael Schulz, R. Moshammer, Daniel Fischer, Ahmad Hasan, N. V. Maydanyuk, J. D. Ullrich Oct 2004

Fully Differential Three-Dimensional Angular Distributions Of Electrons Ionized In Ion-Atom Collisions, Michael Schulz, R. Moshammer, Daniel Fischer, Ahmad Hasan, N. V. Maydanyuk, J. D. Ullrich

Physics Faculty Research & Creative Works

We compare experimental fully differential three-dimensional angular distributions of electrons ionized from He in collision with ionic projectiles covering a broad range of perturbations (0.065 to 4.4). Even at very small perturbations clear signatures of higher-order contributions are observable. At large perturbations, such contributions become even dominant, especially those involving the post-collision interaction between the outgoing projectile and the ionized electron. Our results show that single ionization is not nearly as well understood as was assumed previously.


Nonrelativistic Qed Approach To The Bound-Electron G Factor, Krzysztof Pachucki, Ulrich D. Jentschura, Vladimir A. Yerokhin Oct 2004

Nonrelativistic Qed Approach To The Bound-Electron G Factor, Krzysztof Pachucki, Ulrich D. Jentschura, Vladimir A. Yerokhin

Physics Faculty Research & Creative Works

Within a systematic approach based on nonrelativistic quantum electrodynamics, we derive the one-loop self-energy correction of order α ( Z α )4 to the bound-electron g factor. In combination with numerical data, this analytic result improves theoretical predictions for the self-energy correction for carbon and oxygen by an order of magnitude. Basing on one-loop calculations, we obtain the logarithmic two-loop contribution of order α2 ( Z α )4 ln [ ( Z α )- 2 ] and the dominant part of the corresponding constant term. The results obtained improve the accuracy of the theoretical predictions for the 1 S bound-electron g factor and influence the ...


Electronic Structure Properties And Bcs Superconductivity In ß-Pyrochlore Oxides: KoSS₂O₆, Rolando Saniz, Julia E. Medvedeva, Lin Hui Ye, Tatsuya Shishidou, Arthur J. Freeman Sep 2004

Electronic Structure Properties And Bcs Superconductivity In ß-Pyrochlore Oxides: KoSS₂O₆, Rolando Saniz, Julia E. Medvedeva, Lin Hui Ye, Tatsuya Shishidou, Arthur J. Freeman

Physics Faculty Research & Creative Works

We report a first-principles density-functional calculation of the electronic structure and properties of the recently discovered superconducting β-pyrochlore oxide KOs2O6. We find that the electronic structure near the Fermi energy EF is dominated by strongly hybridized Os 5d and O 2p states. A van Hove singularity very close to Ef leads to a relatively large density of states at EF, and the Fermi surface exhibits strong nesting along several directions. These features could provide the scattering processes leading to the observed anomalous temperature dependence of the resistivity and to the rather large specific-heat mass ...


Electron Loss From 1.4-Mev / U U4,6,10+ Ions Colliding With Ne, N₂, And Ar Targets, Robert D. Dubois, Antonio C. Santos, Th. Stohlker, F. Bosch, A. Brauning-Demian, A. Gumberidze, S. Hagmann, C. Kozhuharov, R. Mann, A. Orsic Muthig, U. Spillman, S. Tachenov, W. Bart, L. Dahl, B. Franzke, J. Glatz, L. Groning, S. Richter, D. Wilms, K. Ullmann, O. Jagutzki Sep 2004

Electron Loss From 1.4-Mev / U U4,6,10+ Ions Colliding With Ne, N₂, And Ar Targets, Robert D. Dubois, Antonio C. Santos, Th. Stohlker, F. Bosch, A. Brauning-Demian, A. Gumberidze, S. Hagmann, C. Kozhuharov, R. Mann, A. Orsic Muthig, U. Spillman, S. Tachenov, W. Bart, L. Dahl, B. Franzke, J. Glatz, L. Groning, S. Richter, D. Wilms, K. Ullmann, O. Jagutzki

Physics Faculty Research & Creative Works

Absolute, total, single- and multiple-electron-loss cross sections are measured for 1.4-MeV / u U4,6,10+ ions colliding with neon and argon atoms and nitrogen molecules. It is found that the cross sections all have the same dependence on the number of electrons lost and that multiplying the cross sections by the initial number of electrons in the 6s, 6p, and 5f shells yields good agreement between the different projectiles. By combining the present data with previous measurements made at the same velocity, it is shown that the scaled cross sections slowly decrease in magnitude for ...


Breakup Of H₂ In Singly Ionizing Collisions With Fast Protons: Channel-Selective Low-Energy Electron Spectra, Christina Dimopoulou, Robert Moshammer, Daniel Fischer, C. Hohr, Alexander Dorn, Pablo Daniel Fainstein, Jose R. Crespo Lopez-Urrutia, Claus Dieter Schroter, Holger Kollmus, Rido Mann, Siegbert Hagmann, Joachim Hermann Ullrich Sep 2004

Breakup Of H₂ In Singly Ionizing Collisions With Fast Protons: Channel-Selective Low-Energy Electron Spectra, Christina Dimopoulou, Robert Moshammer, Daniel Fischer, C. Hohr, Alexander Dorn, Pablo Daniel Fainstein, Jose R. Crespo Lopez-Urrutia, Claus Dieter Schroter, Holger Kollmus, Rido Mann, Siegbert Hagmann, Joachim Hermann Ullrich

Physics Faculty Research & Creative Works

The dissociation of H2 in singly ionizing collisions with fast protons was analyzed using channel-selective low-energy electron spectra. Dissociative and nondissociative single ionization of H2 by 6MeV proton impact was described in a kinematically by determining momentum vectors of electron and H+ fragment of H2+ target ion, respectively. The electron spectra exhibited role of autoionization of doubly and singly excited states of H2. The doubly and singly excited states of H2 involve coupling between electronic and nuclear motion of molecule.


Exotic Versus Conventional Scaling And Universality In A Disordered Bilayer Quantum Heisenberg Antiferromagnet, Rastko Sknepnek, Thomas Vojta, Matthias Vojta Aug 2004

Exotic Versus Conventional Scaling And Universality In A Disordered Bilayer Quantum Heisenberg Antiferromagnet, Rastko Sknepnek, Thomas Vojta, Matthias Vojta

Physics Faculty Research & Creative Works

We present Monte Carlo simulations of a two-dimensional bilayer quantum Heisenberg antiferromagnet with random dimer dilution. In contrast with exotic scaling scenarios found in other random quantum systems, the quantum phase transition in this system is characterized by a finite-disorder fixed point with power-law scaling. After accounting for corrections to scaling, with a leading irrelevant exponent of ω ≈ 0.48, we find universal critical exponents z = 1.310(6) and ν = 1.16(3). We discuss the consequences of these findings and suggest new experiments.


Broadening Of A Nonequilibrium Phase Transition By Extended Structural Defects, Thomas Vojta Aug 2004

Broadening Of A Nonequilibrium Phase Transition By Extended Structural Defects, Thomas Vojta

Physics Faculty Research & Creative Works

We study the effects of quenched extended impurities on nonequilibrium phase transitions in the directed percolation universality class. We show that these impurities have a dramatic effect: they completely destroy the sharp phase transition by smearing. This is caused by rare strongly coupled spatial regions which can undergo the phase transition independently from the bulk system. We use extremal statistics to determine the stationary state as well as the dynamics in the tail of the smeared transition, and we illustrate the results by computer simulations.


Approximately Self-Similar Critical Collapse In 2+1 Dimensions, Marco Cavaglia, Gerard Clement, Alessandro Fabbri Aug 2004

Approximately Self-Similar Critical Collapse In 2+1 Dimensions, Marco Cavaglia, Gerard Clement, Alessandro Fabbri

Physics Faculty Research & Creative Works

Critical collapse of a self-gravitating scalar field in a (2+1)-dimensional spacetime with negative cosmological constant seems to be dominated by a continuously self-similar solution of the field equations without cosmological constant. However, previous studies of linear perturbations in this background were inconclusive. We extend the continuously self-similar solutions to solutions of the field equations with negative cosmological constant, and analyze their linear perturbations. The extended solutions are characterized by a continuous parameter. A suitable choice of this parameter seems to improve the agreement with the numerical results. We also study the dynamics of the apparent horizon in the ...


Hopping Versus Bulk Conductivity In Transparent Oxides: 12cao - 7al₂O₃, Julia E. Medvedeva, Arthur J. Freeman Aug 2004

Hopping Versus Bulk Conductivity In Transparent Oxides: 12cao - 7al₂O₃, Julia E. Medvedeva, Arthur J. Freeman

Physics Faculty Research & Creative Works

First-principles calculations of the mayenite-based oxide, [Ca12Al14O32]2+(2e-), reveal the mechanism responsible for its high conductivity. A detailed comparison of the electronic and optical properties of this material with those of the recently discovered transparent conducting oxide, H-doped UV-activated Ca12Al14O33, allowed us to conclude that the enhanced conductivity in [Ca12Al14O32]2+(2e-) is achieved by elimination of the Coulomb blockade of the charge carriers. This results in a transition from variable range-hopping behavior with a Coulomb gap in H-doped UV-irradiated Ca12Al14 ...


Instantons In Quantum Mechanics And Resurgent Expansions, Ulrich D. Jentschura, Jean Zinn-Justin Aug 2004

Instantons In Quantum Mechanics And Resurgent Expansions, Ulrich D. Jentschura, Jean Zinn-Justin

Physics Faculty Research & Creative Works

Certain quantum mechanical potentials give rise to a vanishing perturbation series for at least one energy level (which as we here assume is the ground state), but the true ground-state energy is positive. We show here that in a typical case, the eigenvalue may be expressed in terms of a generalized perturbative expansion (resurgent expansion). Modified Bohr-Sommerfeld quantization conditions lead to generalized perturbative expansions which may be expressed in terms of nonanalytic factors of the form exp(-a/g), where a>0 is the instanton action, and power series in the coupling g, as well as logarithmic factors. The ground-state ...


Test Of The Pluvinage Wave Function For The Helium Ground State, S. Jones, Joseph H. Macek, Don H. Madison Aug 2004

Test Of The Pluvinage Wave Function For The Helium Ground State, S. Jones, Joseph H. Macek, Don H. Madison

Physics Faculty Research & Creative Works

The accuracy of the Pluvinage wave function for the ground state of helium is investigated by considering a number of different physical processes including double ionization by photoabsorption, Compton scattering, and electron impact. In the high-energy limit of these processes, the accuracy of the initial ground state can be ascertained without reference to the final double-continuum state. In this limit, we find that a Hylleraas description is superior to the Pluvinage one. For intermediate energies, final-state correlation becomes important, so we employ a 3C description of the final state (the 3C wave function is the double-continuum analog of the Pluvinage ...


Erratum: Test Of The Pluvinage Wave Function For The Helium Ground State (Physical Review A - Atomic, Molecular, And Optical Physics (2004) 70 (012712)), Darryl B. Jones, Joseph H. Macek, Don H. Madison Aug 2004

Erratum: Test Of The Pluvinage Wave Function For The Helium Ground State (Physical Review A - Atomic, Molecular, And Optical Physics (2004) 70 (012712)), Darryl B. Jones, Joseph H. Macek, Don H. Madison

Physics Faculty Research & Creative Works

No abstract provided.


Charge Transfer In Slow Collisions Of O⁸⁺ And Ar⁸⁺ Ions With H(1s) Below 2 Kev/Amu, Teck-Ghee Lee, M. Hesse, Anh-Thu Le, C. D. Lin Jul 2004

Charge Transfer In Slow Collisions Of O⁸⁺ And Ar⁸⁺ Ions With H(1s) Below 2 Kev/Amu, Teck-Ghee Lee, M. Hesse, Anh-Thu Le, C. D. Lin

Physics Faculty Research & Creative Works

We calculated the charge-transfer cross sections for O⁸⁺ + H collisions for energies from 1eV/amu to 2keV/amu, using the recently developed hyperspherical close-coupling method. In particular, the discrepancy for electron capture to the n = 6 states of O⁷⁺ from the previous theoretical calculations is further analyzed. Our results indicate that at low energies (below 100eV∕amu) electron capture to the n=6 manifold of O7+ becomes dominant. The present results are used to resolve the long-standing discrepancies from the different elaborate semiclassical calculations near 100eV/amu. We have also performed the semiclassical atomic orbital close-coupling calculations with straight-line trajectories ...


Electronic Structure And Light-Induced Conductivity Of A Transparent Refractory Oxide, Julia E. Medvedeva, Arthur J. Freeman, Mariana I. Bertoni, Thomas O. Mason Jul 2004

Electronic Structure And Light-Induced Conductivity Of A Transparent Refractory Oxide, Julia E. Medvedeva, Arthur J. Freeman, Mariana I. Bertoni, Thomas O. Mason

Physics Faculty Research & Creative Works

Combined first-principles and experimental investigations reveal the underlying mechanism responsible for a drastic change of the conductivity (by 10 orders of magnitude) following hydrogen annealing and UV irradiation in a transparent oxide, 12CaO · 7Al2O3, found by Hayashi et al. [Nature (London) 419, 462 (2002).] The charge transport associated with photoexcitation of an electron from H- occurs by electron hopping.We identify the atoms participating in the hops, determine the exact paths for the carrier migration, estimate the temperature behavior of the hopping transport, and predict a way to enhance the conductivity by specific doping.


Comparison Of Hyperspherical Versus Common-Reaction-Coordinate Close-Coupling Methods For Ion-Atom Collisions At Low Energies, Anh-Thu Le, C. D. Lin, L. F. Errea, L. Mendez, A. Riera, B. Pons Jun 2004

Comparison Of Hyperspherical Versus Common-Reaction-Coordinate Close-Coupling Methods For Ion-Atom Collisions At Low Energies, Anh-Thu Le, C. D. Lin, L. F. Errea, L. Mendez, A. Riera, B. Pons

Physics Faculty Research & Creative Works

We present detailed comparisons between the two quantal approaches--hyperspherical close-coupling and common-reaction-coordinate close-coupling methods--on an exemplary case of He²⁺ + H(1s) collisions at center-of-mass energy from 20eV up to 1.6keV. It is shown that the partial-wave charge-transfer cross sections from the two approaches agree very well at low energy below 200eV down to 30eV. This good agreement is a strong indication of the validity of both methods. The small difference at very low energies and the convergence with respect to the number of channels in both approaches at higher energies are also discussed.


New Limits On The Drift Of Fundamental Constants From Laboratory Measurements, Marc P. Fischer, Nikolai N. Kolachevsky, Marcus Zimmermann, Ronald Holzwarth, Th H. Udem, Theodor Wolfgang Hansch, Michel Abgrall, Jan Grunert, Ivan Maksimovic, Sebastien Bize, Harold Marion, Franck Pereira M Dos Santos, Pierre Lemonde, Giorgio Santarelli, Ph Laurent, Andre Clairon, Christophe Salomon, Martin K. Haas, Ulrich D. Jentschura, Christoph H. Keitel Jun 2004

New Limits On The Drift Of Fundamental Constants From Laboratory Measurements, Marc P. Fischer, Nikolai N. Kolachevsky, Marcus Zimmermann, Ronald Holzwarth, Th H. Udem, Theodor Wolfgang Hansch, Michel Abgrall, Jan Grunert, Ivan Maksimovic, Sebastien Bize, Harold Marion, Franck Pereira M Dos Santos, Pierre Lemonde, Giorgio Santarelli, Ph Laurent, Andre Clairon, Christophe Salomon, Martin K. Haas, Ulrich D. Jentschura, Christoph H. Keitel

Physics Faculty Research & Creative Works

We have remeasured the absolute 1S-2S transition frequency νH in atomic hydrogen. A comparison with the result of the previous measurement performed in 1999 sets a limit of (-29 ± 57) Hz for the drift of νH with respect to the ground state hyperfine splitting νCs in 133Cs. Combining this result with the recently published optical transition frequency in 199Hg+ against νCs and a microwave 87Rb and 133Cs clock comparison, we deduce separate limits on α˙ / α = (-0.9 &plusm; 2.9) x 10-15 yr-1 and the fractional time variation of the ...


Electron Self-Energy For Higher Excited S Levels, Ulrich D. Jentschura, Peter J. Mohr Jun 2004

Electron Self-Energy For Higher Excited S Levels, Ulrich D. Jentschura, Peter J. Mohr

Physics Faculty Research & Creative Works

A nonperturbative numerical evaluation of the one-photon electron self-energy for the 3S and 4S states with charge numbers Z=1 to 5 is described. The numerical results are in agreement with known terms in the expansion of the self-energy in powers of Zα.


Close-Coupling And Distorted-Wave Calculations For Electron-Impact Excitation Of The (5p⁵6p) States Of Xenon, K. Bartschat, Anand Dasgupta, Don H. Madison Jun 2004

Close-Coupling And Distorted-Wave Calculations For Electron-Impact Excitation Of The (5p⁵6p) States Of Xenon, K. Bartschat, Anand Dasgupta, Don H. Madison

Physics Faculty Research & Creative Works

We report on a series of calculations for electron-impact excitation of the (5p56p) states in xenon from the ground state (5p6)1S0 . As in previous calculations for other noble-gas targets, we find strong evidence of channel coupling for all incident energies considered (between threshold and 200 eV ). Although qualitative agreement with the experimental results of Fons and Lin [Phys. Rev. A 58, 4603 (1998)] is achieved, severe quantitative discrepancies of sometimes more than a factor of 2 remain.


Gravitational Energy Loss In High Energy Particle Collisions: Ultrarelativistic Plunge Into A Multidimensional Black Hole, Emanuele Berti, Marco Cavaglia, Leonardo Gualtieri Jun 2004

Gravitational Energy Loss In High Energy Particle Collisions: Ultrarelativistic Plunge Into A Multidimensional Black Hole, Emanuele Berti, Marco Cavaglia, Leonardo Gualtieri

Physics Faculty Research & Creative Works

We investigate the gravitational energy emission of an ultrarelativistic particle radially falling into a D-dimensional black hole. We numerically integrate the equations describing black hole gravitational perturbations and obtain the energy spectra, total energy, and angular distribution of the emitted gravitational radiation. The black hole quasinormal modes for scalar, vector, and tensor perturbations are computed in the WKB approximation. We discuss our results in the context of black hole production at the TeV scale.


Self-Energy Correction To The Two-Photon Decay Width In Hydrogenlike Atoms, Ulrich D. Jentschura May 2004

Self-Energy Correction To The Two-Photon Decay Width In Hydrogenlike Atoms, Ulrich D. Jentschura

Physics Faculty Research & Creative Works

We investigate the guage invariance of the leading logarithmic radiative correction to the two-photon decay width in hydrogenlike atoms, was investigated. The effective treatment of the correction using a Lamb-shift led to the equivalent results in both the length and velocity gages. The relevant radiative corrections were found to be related to the energies that entered into the propagator denominators, to the Hamiltonian, to the wave functions, and to the energy conservation condition, that holds between two photons. The results show that the dominant radiative correction to the 2S two-photon decay width is about -2.020 536(α/π)(Zα ...


Protonium Formation In The P̅-H Collision At Low Energies By A Diabatic Approach, M. Hesse, Anh-Thu Le, C. D. Lin May 2004

Protonium Formation In The P̅-H Collision At Low Energies By A Diabatic Approach, M. Hesse, Anh-Thu Le, C. D. Lin

Physics Faculty Research & Creative Works

We present a diabatization technique in combination with the recently developed hyperspherical close coupling (HSCC) method. In contrast to the strict diabatization, our simple diabatization procedure transforms only sharp avoided crossings in the adiabatic hyperspherical potential curves into real crossings. With this approach, the weak collision channels can be removed from the close-coupling calculations. This method is used to study the antiproton-hydrogen collision at low energies. In the case of a scaled down (anti)proton mass, we show that a 10-channel calculation is enough to obtain converged cross sections at low energies. The results also indicate that protonium formation occurs ...


Comment On "Role Of The Ground State In Electron-Atom Double Ionization" [1] (Multiple Letters), Jamal Berakdar, Stephenie J. Jones, Don H. Madison Apr 2004

Comment On "Role Of The Ground State In Electron-Atom Double Ionization" [1] (Multiple Letters), Jamal Berakdar, Stephenie J. Jones, Don H. Madison

Physics Faculty Research & Creative Works

No abstract provided.


Scaling Laws For Single And Multiple Electron Loss From Projectiles In Collisions With A Many-Electron Target, Antonio C. Santos, Robert D. Dubois Apr 2004

Scaling Laws For Single And Multiple Electron Loss From Projectiles In Collisions With A Many-Electron Target, Antonio C. Santos, Robert D. Dubois

Physics Faculty Research & Creative Works

Using measured cross sections, empirical scaling laws are extracted for projectile stripping induced by collisions with a many-electron target. by scaling both the cross sections and the impact velocities, it is shown that a single universal curve can be used to fit data for single and multiple electron loss from negative ions, neutral particles, and singly or multiply charged positive ions. The scaling applies to projectiles ranging from hydrogen to uranium and collision energies ranging from below keV∕u to hundreds of MeV∕u . At high energies, existing data are consistent with a v−1 impact velocity dependence for scaled ...


Doubly Differential Multiple Ionization Of Krypton By Positron And Electron Impact, Kay Dubois, Antonio C. Santos, Ahmad Hasan Mar 2004

Doubly Differential Multiple Ionization Of Krypton By Positron And Electron Impact, Kay Dubois, Antonio C. Santos, Ahmad Hasan

Physics Faculty Research & Creative Works

Measurements of doubly differential single and multiple ionization of krypton atoms have been performed for 750 eV positron and electron impact. Data were measured as a function of projectile energy-loss and scattering angle. For electrons, the energy-loss range was 0-85% of the initial projectile energy and scattering angles were between ±22°. Following the procedure adopted previously for argon, the electron impact data were placed on an absolute scale by normalizing to total ionization cross sections available in the literature. The present results for krypton show differences between positron and electron impact that are less pronounced than was found for argon ...


Order-Parameter Symmetry And Mode-Coupling Effects At Dirty Superconducting Quantum Phase Transitions, Rastko Sknepnek, Thomas Vojta, Rajesh Narayanan Jan 2004

Order-Parameter Symmetry And Mode-Coupling Effects At Dirty Superconducting Quantum Phase Transitions, Rastko Sknepnek, Thomas Vojta, Rajesh Narayanan

Physics Faculty Research & Creative Works

We derive an order-parameter field theory for a quantum phase transition between a disordered metal and an exotic (non- s -wave) superconductor. Mode coupling effects between the order parameter and other fermionic soft modes lead to an effective long-range interaction between the anomalous density fluctuations which is reflected in singularities in the free energy functional. However, this long-range interaction is not strong enough to suppress disorder fluctuations. The asymptotic critical region is characterized by run-away flow to large disorder. For weak coupling, this asymptotic region is very narrow. It is preempted by a wide crossover regime with mean-field critical behavior ...


Ultraviolet Photonic Crystal Laser, Alexey Yamilov, Hui Cao, Robert P. H. Chang, Xiaohua Wu, Xang Liu, Shuyou Li, Vinayak P. Dravid Jan 2004

Ultraviolet Photonic Crystal Laser, Alexey Yamilov, Hui Cao, Robert P. H. Chang, Xiaohua Wu, Xang Liu, Shuyou Li, Vinayak P. Dravid

Physics Faculty Research & Creative Works

We fabricated two-dimensional photonic crystal structures in zinc oxide films with focused-ion-beam etching. Lasing is realized in the near-ultraviolet frequency at room temperature under optical pumping. From the measurement of lasing frequency and spatial profile of the lasing modes, as well as the photonic band structure calculation, we conclude that lasing occurs in the strongly localized defect modes near the edges of photonic band gap. These defect modes originate from the structure disorder unintentionally introduced during the fabrication process. ©2004 American Institute of Physics