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Physics Faculty Research & Creative Works

1999

Articles 1 - 14 of 14

Full-Text Articles in Physical Sciences and Mathematics

Initial State Dependence Of Low-Energy Electron Emission In Fast Ion Atom Collisions, Robert Moshammer, Pablo Daniel Fainstein, Michael Schulz, Wayne M. Schmitt, Holger Kollmus, Rido Mann, Siegbert Hagmann, Joachim Hermann Ullrich Dec 1999

Initial State Dependence Of Low-Energy Electron Emission In Fast Ion Atom Collisions, Robert Moshammer, Pablo Daniel Fainstein, Michael Schulz, Wayne M. Schmitt, Holger Kollmus, Rido Mann, Siegbert Hagmann, Joachim Hermann Ullrich

Physics Faculty Research & Creative Works

Single and multiple ionization of neon and argon atoms by 3.6 MeV/u Au53+ impact has been explored in kinematically complete experiments. Doubly differential cross sections for low-energy electron emission have been obtained for a defined charge state of the recoiling target ion and the receding projectile. Observed target specific structures in the electron continuum are attributable to the nodal structure of the initial bound state momentum distribution. The experimental data are in excellent accord with continuum-distorted-wave eikonal-initial-state single ionization calculations if multiple ionization is considered appropriately.


Laser-Induced Stabilization Of Autoionizing States, Heider N. Ereifej, J. Greg Story Nov 1999

Laser-Induced Stabilization Of Autoionizing States, Heider N. Ereifej, J. Greg Story

Physics Faculty Research & Creative Works

Stabilization of autoionizing states of barium by laser-induced, stimulated emission of light is demonstrated. Relative to purely flourescent stabilization, the data clearly show an enhancement of the stabilization process for laser pulses short compared to the flourescent lifetime of the autoionizing states. Shakeup spectra in which the principal quantum number of both electrons changes during the stimulated emission process are also clearly demonstrated.


Doppler Shift Anisotropy In Small Angle Neutron Scattering, Barbara Ellen Wyslouzil, Gerald Wilemski, Janice L. Cheung, Reinhard Strey, John G. Barker Oct 1999

Doppler Shift Anisotropy In Small Angle Neutron Scattering, Barbara Ellen Wyslouzil, Gerald Wilemski, Janice L. Cheung, Reinhard Strey, John G. Barker

Physics Faculty Research & Creative Works

The two-dimensional patterns in our small angle neutron scattering (SANS) experiments from rapidly moving aerosols are anisotropic. To test the kinematic theory of two-body scattering that describes the anisotropy, we conducted SANS experiments using a constant source of D2O aerosol with droplets moving at ~440 m/s, and varied the neutron velocity from 267 to 800 m/s. The theoretically predicted anisotropy of the laboratory scattering intensities agrees well with the experimental results. Based on an analysis of the scattering intensity in the Guinier region, we also determined the particle velocity. The results are in very good agreement ...


Critical Behavior Of Disordered Quantum Magnets: The Relevance Of Rare Regions, Rajesh S. Narayanan, Thomas Vojta, Dietrich Belitz, Theodore R. Kirkpatrick Oct 1999

Critical Behavior Of Disordered Quantum Magnets: The Relevance Of Rare Regions, Rajesh S. Narayanan, Thomas Vojta, Dietrich Belitz, Theodore R. Kirkpatrick

Physics Faculty Research & Creative Works

The effects of quenched disorder on the critical properties of itinerant quantum antiferromagnets and ferromagnets are considered. Particular attention is paid to locally ordered spatial regions that are formed in the presence of quenched disorder even when the bulk system is still in the paramagnetic phase. These rare regions or local moments are reflected in the existence of spatially inhomogeneous saddle points of the Landau-Ginzburg-Wilson functional. We derive an effective theory that takes into account small fluctuations around all of these saddle points. The resulting free energy functional contains a new term in addition to those obtained within the conventional ...


Investigation Of Resonant Photoemission In Gd With X-Ray Linear Dichroism, Shubhra R. Mishra, Thomas K. Cummins, George Daniel Waddill, W. J. Gammon, Gerrit V. Van Der Laan, Kyle W. Goodman, James G. Tobin Jul 1999

Investigation Of Resonant Photoemission In Gd With X-Ray Linear Dichroism, Shubhra R. Mishra, Thomas K. Cummins, George Daniel Waddill, W. J. Gammon, Gerrit V. Van Der Laan, Kyle W. Goodman, James G. Tobin

Physics Faculty Research & Creative Works

The constructive summing of direct and indirect channels above the absorption threshold of a core level can cause a massive increase in the emission cross section, leading to a phenomenon called "resonant photoemission." Using novel magnetic linear dichroism in angular distribution photoelectron spectroscopy experiments and theoretical simulations, we have probed the nature of the resonant photoemission process in Gd metal. It now appears that temporal matching as well as energy matching is a requirement for true resonant photoemission.


Influence Of Rare Regions On Magnetic Quantum Phase Transitions, Rajesh S. Narayanan, Thomas Vojta, Dietrich Belitz, Theodore R. Kirkpatrick Jun 1999

Influence Of Rare Regions On Magnetic Quantum Phase Transitions, Rajesh S. Narayanan, Thomas Vojta, Dietrich Belitz, Theodore R. Kirkpatrick

Physics Faculty Research & Creative Works

The effects of quenched disorder on the critical properties of itinerant quantum magnets are considered. Particular attention is paid to locally ordered rare regions that are formed in the presence of quenched disorder even when the bulk system is still in the nonmagnetic phase. It is shown that these local moments or instantons destroy the previously found critical fixed point in the case of antiferromagnets. In the case of itinerant ferromagnets, the critical behavior is unaffected by the rare regions due to an effective long-range interaction between the order parameter fluctuations.


First Order Transitions And Multicritical Points In Weak Itinerant Ferromagnets, Dietrich Belitz, Theodore R. Kirkpatrick, Thomas Vojta Jun 1999

First Order Transitions And Multicritical Points In Weak Itinerant Ferromagnets, Dietrich Belitz, Theodore R. Kirkpatrick, Thomas Vojta

Physics Faculty Research & Creative Works

It is shown that the phase transition in low-Tc clean itinerant ferromagnets is generically of first order, due to correlation effects that lead to a nonanalytic term in the free energy. A tricritical point separates the line of first order transitions from Heisenberg critical behavior at higher temperatures. Sufficiently strong quenched disorder suppresses the first order transition via the appearance of a critical end point. A semiquantitative discussion is given in terms of recent experiments on MnSi, and predictions for other experiments are made.


Effects Of Resonant Tunneling In Electromagnetic Wave Propagation Through A Polariton Gap, Lev I. Deych, Alexey Yamilov, Alexander A. Lisyansky May 1999

Effects Of Resonant Tunneling In Electromagnetic Wave Propagation Through A Polariton Gap, Lev I. Deych, Alexey Yamilov, Alexander A. Lisyansky

Physics Faculty Research & Creative Works

We consider tunneling of electromagnetic waves through a polariton band gap of a one-dimensional chain of atoms. We analytically show that a defect embedded in the structure gives rise to the resonance transmission at the frequency of a local polariton state associated with the defect. Numerical Monte Carlo simulations are used to examine properties of the electromagnetic band arising inside the polariton gap due to finite concen-tration of defects.


Defect-Induced Resonant Tunneling Of Electromagnetic Waves Through A Polariton Gap, Lev I. Deych, Alexey Yamilov, Alexander A. Lisyansky May 1999

Defect-Induced Resonant Tunneling Of Electromagnetic Waves Through A Polariton Gap, Lev I. Deych, Alexey Yamilov, Alexander A. Lisyansky

Physics Faculty Research & Creative Works

We consider tunneling of electromagnetic waves through a polariton band gap of a 1-D chain of atoms. We analytically demonstrate that a defect embedded in the structure gives rise to the resonance transmission at the frequency of a local polariton state associated with the defect.


Binary Nucleation Kinetics. Iv. Directional Properties And Cluster Concentrations At The Saddle Point, Gerald Wilemski Apr 1999

Binary Nucleation Kinetics. Iv. Directional Properties And Cluster Concentrations At The Saddle Point, Gerald Wilemski

Physics Faculty Research & Creative Works

Using a new approach, Stauffer's expression for the rate of steady state binary nucleation and Trinkaus's expression for the steady state cluster concentrations f are derived directly from the diffusion equation that governs the evolution of f in composition space. The behavior of φ (≡f/N, where N is the equilibrium cluster concentration) is explored since this function provides a characterization of the nucleating binary system that, to lowest order, is independent of the actual composition of the mother phase. The angle ω that describes the direction of ▽ φ at the saddle point differs, in general, from the ...


Geometrodynamical Formulation Of Two-Dimensional Dilaton Gravity, Marco Cavaglia Mar 1999

Geometrodynamical Formulation Of Two-Dimensional Dilaton Gravity, Marco Cavaglia

Physics Faculty Research & Creative Works

Two-dimensional matterless dilaton gravity with an arbitrary dilatonic potential can be discussed in a unitary way, both in the Lagrangian and canonical frameworks, by introducing suitable field redefinitions. The new fields are directly related to the original spacetime geometry and in the canonical picture they generalize the well-known geometrodynamical variables used in the discussion of the Schwarzschild black hole. So the model can be quantized using the techniques developed for the latter case. The resulting quantum theory exhibits the Birkhoff theorem at the quantum level.


X-Ray Absorption, Neutron Diffraction, And Mössbauer Effect Studies Of Mnzn-Ferrite Processed Through High-Energy Ball Milling, D. J. Fatemi, V. G. Harris, Mingxing Chen, Satish K. Malik, William B. Yelon, Gary J. Long, Amitabh Mohan Jan 1999

X-Ray Absorption, Neutron Diffraction, And Mössbauer Effect Studies Of Mnzn-Ferrite Processed Through High-Energy Ball Milling, D. J. Fatemi, V. G. Harris, Mingxing Chen, Satish K. Malik, William B. Yelon, Gary J. Long, Amitabh Mohan

Physics Faculty Research & Creative Works

MnZn-ferrite has been prepared via high-energy ball milling of elemental oxides MnO, ZnO, and α-Fe2O3. Neutron diffraction measurements suggest a high density of vacancies in a spinel structure. The spinel phase appears to comprise 99.8 wt % of the material in the sample milled for 40 h, with the remainder attributable to unreacted α-Fe2O3. The x-ray absorption near-edge structure was analyzed to provide an understanding of the charge state of the constituent Fe ions. This analysis reveals about 2/3 of Fe cations to be trivalent, increasing to about 3/4 after a 5 ...


Magnetic And Crystallographic Properties Of Lani₅₋ₓFex, C. Tan, Oran Allan Pringle, Mingxing Chen, William B. Yelon, J. Gebhardt, Naushad Ali, C. Y. Tai, G. K. Marasinghe, George Daniel Waddill, William Joseph James Jan 1999

Magnetic And Crystallographic Properties Of Lani₅₋ₓFex, C. Tan, Oran Allan Pringle, Mingxing Chen, William B. Yelon, J. Gebhardt, Naushad Ali, C. Y. Tai, G. K. Marasinghe, George Daniel Waddill, William Joseph James

Physics Faculty Research & Creative Works

No abstract provided.


Calculation Of The Electron Self-Energy For Low Nuclear Charge, Ulrich D. Jentschura, Peter J. Mohr, Gerhard Soff Jan 1999

Calculation Of The Electron Self-Energy For Low Nuclear Charge, Ulrich D. Jentschura, Peter J. Mohr, Gerhard Soff

Physics Faculty Research & Creative Works

We present a nonperturbative numerical evaluation of the one-photon electron self-energy for hydrogenlike ions with low nuclear charge numbers Z = 1 to 5. Our calculation for the 1S state has a numerical uncertainty of 0.8 Hz for hydrogen and 13 Hz for singly ionized helium. Resummation and convergence acceleration techniques that reduce the computer time by about 3 orders of magnitude were employed in the calculation. The numerical results are compared to results based on known terms in the expansion of the self-energy in powers of Zα.