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Articles 31 - 50 of 50
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Magnetically Mediated Transparent Conductors: In₂O₃ Doped With Mo, Julia E. Medvedeva
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.
Initial-State Correlation Effects In Low-Energy Proton Impact Ionization, M. Foster, Jerry Peacher, Ahmad Hasan, Michael Schulz, Don H. Madison
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 …
Percolation Transition And Dissipation In Quantum Ising Magnets, Jose A. Hoyos, Thomas Vojta
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 …
Theoretical Treatment Of Electron-Impact Ionization Of Molecules, Junfang Gao, Jerry Peacher, Don H. Madison
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
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
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.
Kinematically Complete Experiment On Transfer Excitation In Intermediate-Energy P + He Collisions, Ahmad Hasan, B. Tooke, M. Zapukhlyak, T. Kirchner, Michael Schulz
Kinematically Complete Experiment On Transfer Excitation In Intermediate-Energy P + He Collisions, Ahmad Hasan, B. Tooke, M. Zapukhlyak, T. Kirchner, Michael Schulz
Physics Faculty Research & Creative Works
We have performed a kinematically complete experiment on transfer excitation in intermediate-energy proton-helium collisions. The differential cross sections were compared to double excitation data and a nonperturbative time-dependent calculation. This comparison reveals the importance of dynamic couplings between the motion of the heavy nuclei and electronic transitions and/or electron-electron correlation effects.
Self-Optimization Of Optical Confinement In An Ultraviolet Photonic Crystal Slab Laser, Alexey Yamilov, X. Wu, X. Liu, Hui Cao, Robert P. H. Chang
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.
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
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 …
Quantum Phase Transitions Of The Diluted O(3) Rotor Model, Thomas Vojta, Rastko Sknepnek
Quantum Phase Transitions Of The Diluted O(3) Rotor Model, Thomas Vojta, Rastko Sknepnek
Physics Faculty Research & Creative Works
We study the phase diagram and the quantum phase transitions of a site-diluted two-dimensional O(3) quantum rotor model by means of large-scale Monte Carlo simulations. This system has two quantum phase transitions: a generic one for small dilutions and a percolation transition across the lattice percolation threshold. We determine the critical behavior for both transitions and for the multicritical point that separates them. In contrast to the exotic scaling scenarios found in other random quantum systems, all these transitions are characterized by finite-disorder fixed points with power-law scaling. We relate our findings to a recent classification of phase transitions with …
Kinetic Correlation In Photo-Double-Ionization Processes: The He-Isoelectronic Sequence, Sebastian Otranto, C. R. Garibotti
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
Nonequilibrium Phase Transition On A Randomly Diluted Lattice, Thomas Vojta, Man Young Lee
Nonequilibrium Phase Transition On A Randomly Diluted Lattice, Thomas Vojta, Man Young Lee
Physics Faculty Research & Creative Works
We show that the interplay between geometric criticality and dynamical fluctuations leads to a novel universality class of the contact process on a randomly diluted lattice. The nonequilibrium phase transition across the percolation threshold of the lattice is characterized by unconventional activated (exponential) dynamical scaling and strong Griffiths effects. We calculate the critical behavior in two and three space dimensions, and we also relate our results to the recently found infinite-randomness fixed point in the disordered one-dimensional contact process.
Slow Dynamics At The Smeared Phase Transition Of Randomly Layered Magnets, Shellie Huether, Ryan Kinney, Thomas Vojta
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 …
Ultraviolet Lasing In High-Order Bands Of Three-Dimensional Zno Photonic Crystals, Michael Scharrer, Alexey Yamilov, Xiaohua Wu, Hui Cao, Robert P. H. Chang
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 …
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
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 …
Effect Of Amplification On Conductance Distribution Of A Disordered Waveguide, Alexey Yamilov, Hui Cao
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).
Adiabatic-Nonadiabatic Transition In The Diffusive Hamiltonian Dynamics Of A Classical Holstein Polaron, Alex A. Silvius, Paul Ernest Parris, Stephan De Bièvre
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 …
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
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.
Spin Excitations In Fluctuating Stripe Phases Of Doped Cuprate Superconductors, Matthias Vojta, Thomas Vojta, Ribhu K. Kaul
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.
Crystal And Electronic Structures Of Linh₂, Jinbo Yang, X.-D. Zhou, Qingsheng Cai, William Joseph James, William B. Yelon
Crystal And Electronic Structures Of Linh₂, Jinbo Yang, X.-D. Zhou, Qingsheng Cai, William Joseph James, William B. Yelon
Materials Science and Engineering Faculty Research & Creative Works
The crystal structure of LiNH2 was reinvestigated using powder neutron diffraction with high sensitivity. The compound crystallizes in the tetragonal space group I4 with lattice parameters α = b= 5.034 42 (24) Å, c = 10.255 58 (52) Å. It is found that H atoms occupy 8g1(0.2429, 0.1285, 0.1910) and 8g2 (0.3840, 0.3512, 0.1278) sites. The bond lengths between the nearest nitrogen and hydrogen atoms are 0.986 and 0.942 Å, respectively. The bond angle between H-N-H is about 99.97°. These results are significantly different from those of previous experiments. The electronic structure was calculated according to the revised structural …
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
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 …