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Full-Text Articles in Physical Sciences and Mathematics

Effect Of Rare Locally Ordered Regions On A Disordered Itinerant Quantum Antiferromagnet With Cubic Anisotropy, Rajesh S. Narayanan, Thomas Vojta Dec 2001

Effect Of Rare Locally Ordered Regions On A Disordered Itinerant Quantum Antiferromagnet With Cubic Anisotropy, Rajesh S. Narayanan, Thomas Vojta

Physics Faculty Research & Creative Works

We study the quantum phase transition of an itinerant antiferromagnet with cubic anisotropy in the presence of quenched disorder, paying particular attention to the locally ordered spatial regions that form in the Griffiths region. We derive an effective action where these rare regions are described in terms of static annealed disorder. A one-loop renormalization-group analysis of the effective action shows that for order-parameter dimensions p<4, the rare regions destroy the conventional critical behavior, and the renormalized disorder flows to infinity. For order-parameter dimensions p>4, the critical behavior is not influenced by the rare regions; it is described by the conventional dirty cubic fixed point. We also discuss the influence of the rare regions on the fluctuation-driven first-order transition ...


Electron-Impact Excitation To The 4p⁵5s And 4p⁵5p Levels Of Kr | Using Different Distorted-Wave And Close-Coupling Methods, Arati K. Dasgupta, Klaus Bartschat, D. Vaid, Alexei N. Grum-Grzhimailo, Don H. Madison, Milan Blaha, John L. Giuliani Nov 2001

Electron-Impact Excitation To The 4p⁵5s And 4p⁵5p Levels Of Kr | Using Different Distorted-Wave And Close-Coupling Methods, Arati K. Dasgupta, Klaus Bartschat, D. Vaid, Alexei N. Grum-Grzhimailo, Don H. Madison, Milan Blaha, John L. Giuliani

Physics Faculty Research & Creative Works

Electron-impact excitation of the 4p55s and 4p55p levels of Kr I has been investigated in detail by calculating cross sections using distorted-wave and close-coupling approaches. The results are presented from the excitation thresholds up to 50 eV incident energy. They are contrasted among the different calculations and compared with other theoretical predictions and experimental data. Significant disagreement is found with many of the recent experimental data of Chilton et al. [Phys. Rev. A 62, 032714 (2000)].


Three-Body Coulomb Problem Probed By Mapping The Bethe Surface In Ionizing Ion-Atom Collisions, Robert Moshammer, Appathurai N. Perumal, Michael Schulz, V. D. Rodriguez, Holger Kollmus, Rido Mann, Siegbert Hagmann, Joachim Hermann Ullrich Nov 2001

Three-Body Coulomb Problem Probed By Mapping The Bethe Surface In Ionizing Ion-Atom Collisions, Robert Moshammer, Appathurai N. Perumal, Michael Schulz, V. D. Rodriguez, Holger Kollmus, Rido Mann, Siegbert Hagmann, Joachim Hermann Ullrich

Physics Faculty Research & Creative Works

The three-body Coulomb problem has been explored in kinematically complete experiments on single ionization of helium by 100 MeV / u C 6 + and 3.6 MeV / u u 5 3 + impact. Low-energy electron emission (E e < 150 eV ) as a function of the projectile deflection ϑ p (momentum transfer), i.e., the Bethe surface [[15]], has been mapped with Δ ϑ p ± 25 nanoradian resolution at extremely large perturbations (3.6 MeV / uAu53+ ) where single ionization occurs at impact parameters of typically 10 times the He K -shell radius. The experimental data are not in agreement with state-of-the-art continuum distorted wave-eikonal initial state theory.


Magnetic Properties Of The Mnbi Intermetallic Compound, Jinbo Yang, Kishore Kamaraju, William B. Yelon, William Joseph James, Qingsheng Cai, A. Bollero Sep 2001

Magnetic Properties Of The Mnbi Intermetallic Compound, Jinbo Yang, Kishore Kamaraju, William B. Yelon, William Joseph James, Qingsheng Cai, A. Bollero

Physics Faculty Research & Creative Works

A MnBi alloy containing over 90 wt% low-temperature phase (LTP) has been obtained by high-temperature sintering and magnetic purification. The coercivity of the bonded MnBi magnet increases with increasing temperatures. A coercivity of 2.0 T has been achieved at 400 K. The maximum energy product (BH)max; of the magnet is 7.7 MGOe (61 kJ/m3) and 4.6 MGOe (37 kJ/m3) at room temperature and 400 K, respectively. Neutron diffraction and magnetic data reveal a spin reorientation, which gives rise to low anisotropy fields and coercivity at lower temperatures for the LTP MnBi alloy.


Nature Of Charge Carriers In Disordered Molecular Solids: Are Polarons Compatible With Observations?, Paul Ernest Parris, Vasudev M. Kenkre, David H. Dunlap Sep 2001

Nature Of Charge Carriers In Disordered Molecular Solids: Are Polarons Compatible With Observations?, Paul Ernest Parris, Vasudev M. Kenkre, David H. Dunlap

Physics Faculty Research & Creative Works

Polaronic theories for charge transport in disordered organic solids, particularly molecularly doped polymers, have been plagued by issues of internal consistency related to the magnitude of physical parameters. We present a natural resolution of the problem by showing that, in the presence of correlated disorder, polaronic carriers with binding energies Δ ~ 50 - 500 meV and transfer integrals J ~ 1 - 20 meV are completely consistent with the magnitudes of field and temperature dependent mobilities observed.


Tunable Local Polariton Modes In Semiconductors, Michael G. Foygel, Alexey Yamilov, Lev I. Deych, Alexander A. Lisyansky Sep 2001

Tunable Local Polariton Modes In Semiconductors, Michael G. Foygel, Alexey Yamilov, Lev I. Deych, Alexander A. Lisyansky

Physics Faculty Research & Creative Works

We study the local states within the polariton band gap that arise due to deep defect centers with strong electron-phonon coupling. Electron transitions involving deep levels may result in alteration of local elastic constants. In this case, substantial reversible transformations of the impurity polariton density of states occur, which include the appearance/disappearance of the polariton impurity band, and its shift and/or the modification of its shape. These changes can be induced by thermo- and photoexcitation of the localized electron states or by trapping of injected charge carriers. We develop a simple model, which is applied to the O ...


Strong Enhancement Of Superconducting TC In Ferromagnetic Phases, Theodore R. Kirkpatrick, Dietrich Belitz, Thomas Vojta, Rajesh S. Narayanan Sep 2001

Strong Enhancement Of Superconducting TC In Ferromagnetic Phases, Theodore R. Kirkpatrick, Dietrich Belitz, Thomas Vojta, Rajesh S. Narayanan

Physics Faculty Research & Creative Works

It is shown that the critical temperature for spin-triplet, p-wave superconductivity mediated by spin fluctuations is generically much higher in a Heisenberg ferromagnetic phase than in a paramagnetic one, due to the coupling of the magnons to the longitudinal magnetic susceptibility. Together with the tendency of the low-temperature ferromagnetic transition in very clean Heisenberg magnets to be of first order, this qualitatively explains the phase diagram recently observed in UGe2.


Quantum Phase Transition Of Itinerant Helimagnets, Thomas Vojta, Rastko Sknepnek Aug 2001

Quantum Phase Transition Of Itinerant Helimagnets, Thomas Vojta, Rastko Sknepnek

Physics Faculty Research & Creative Works

We investigate the quantum phase transition of itinerant electrons from a paramagnet to a state which displays long-period helical structures due to a Dzyaloshinskii instability of the ferromagnetic state. In particular, we study how the self-generated effective long-range interaction recently identified in itinerant quantum ferromagnets is cut off by the helical ordering. We find that for a sufficiently strong Dzyaloshinskii instability the helimagnetic quantum phase transition is of second order with mean-field exponents. In contrast, for a weak Dzyaloshinskii instability the transition is analogous to that in itinerant quantum ferromagnets, i.e., it is of first order, as has been ...


Resummation Of The Divergent Perturbation Series For A Hydrogen Atom In An Electric Field, Ulrich D. Jentschura Jul 2001

Resummation Of The Divergent Perturbation Series For A Hydrogen Atom In An Electric Field, Ulrich D. Jentschura

Physics Faculty Research & Creative Works

We consider the resummation of the perturbation series describing the energy displacement of a hydrogenic bound state in an electric field (known as the Stark effect or the LoSurdo-Stark effect), which constitutes a divergent formal power series in the electric-field strength. The perturbation series exhibits a rich singularity structure in the Borel plane. Resummation methods are presented that appear to lead to consistent results even in problematic cases where isolated singularities or branch cuts are present on the positive and negative real axis in the Borel plane. Two resummation prescriptions are compared: (i) a variant of the Borel-Pad'e resummation ...


Local Polariton Modes And Resonant Tunneling Of Electromagnetic Waves Through Periodic Bragg Multiple Quantum Well Structures, Lev I. Deych, Alexey Yamilov, Alexander A. Lisyansky Jul 2001

Local Polariton Modes And Resonant Tunneling Of Electromagnetic Waves Through Periodic Bragg Multiple Quantum Well Structures, Lev I. Deych, Alexey Yamilov, Alexander A. Lisyansky

Physics Faculty Research & Creative Works

We study analytically defect polariton states in Bragg multiple quantum well structures and defect-induced changes in transmission and reflection spectra. Defect layers can differ from the host layers in three ways: exciton-light coupling strength, exciton resonance frequency, and interwell spacing. We show that a single defect leads to two local polariton modes in the photonic band gap. These modes cause peculiarities in reflection and transmission spectra. Each type of defect can be reproduced experimentally, and we show that each of these plays a distinct role in the optical properties of the system. For some defects, we predict a narrow transmission ...


Separation Of Recollision Mechanisms In Nonsequential Strong Field Double Ionization Of Ar: The Role Of Excitation Tunneling, Bernold Feuerstein, Daniel Fischer, Alexander Dorn, Claus Dieter Schroter, J. Deipenwisch, Jose R. Crespo Lopez-Urrutia, C. Hohr, Paul B. Neumayer, Horst Rottke, Christoph Trump, M. Wittmann, Georg Korn, Wolfgang Sandner, Robert Moshammer, Joachim Hermann Ullrich Jul 2001

Separation Of Recollision Mechanisms In Nonsequential Strong Field Double Ionization Of Ar: The Role Of Excitation Tunneling, Bernold Feuerstein, Daniel Fischer, Alexander Dorn, Claus Dieter Schroter, J. Deipenwisch, Jose R. Crespo Lopez-Urrutia, C. Hohr, Paul B. Neumayer, Horst Rottke, Christoph Trump, M. Wittmann, Georg Korn, Wolfgang Sandner, Robert Moshammer, Joachim Hermann Ullrich

Physics Faculty Research & Creative Works

Vector momentum distributions of two electrons created in double ionization of Ar by 25 fs, 0.25PW/cm2 laser pulses at 795 nm have been measured using a “reaction microscope.” At this intensity, where nonsequential ionization dominates, distinct correlation patterns are observed in the two-electron momentum distributions. A kinematical analysis of these spectra within the classical “recollision model” revealed an (e,2e)-like process and excitation with subsequent tunneling of the second electron as two different ionization mechanisms. This allows a qualitative separation of the two mechanisms demonstrating that excitation-tunneling is the dominant contribution to the total double ionization ...


Scaling In One-Dimensional Localized Absorbing Systems, Lev I. Deych, Alexey Yamilov, Alexander A. Lisyansky Jun 2001

Scaling In One-Dimensional Localized Absorbing Systems, Lev I. Deych, Alexey Yamilov, Alexander A. Lisyansky

Physics Faculty Research & Creative Works

Numerical study of the scaling of transmission fluctuations in the one-dimensional localization problem in the presence of absorption is carried out. Violations of single-parameter scaling for lossy systems are found and explained on the basis of a new criterion for different types of scaling behavior derived by Deych et al.


Electronic Structure Of Superconducting Mgb₂ And Related Binary And Ternary Borides, Nadezhda I. Medvedeva, Alexander L. Ivanovskii, Julia E. Medvedeva, Arthur J. Freeman Jun 2001

Electronic Structure Of Superconducting Mgb₂ And Related Binary And Ternary Borides, Nadezhda I. Medvedeva, Alexander L. Ivanovskii, Julia E. Medvedeva, Arthur J. Freeman

Physics Faculty Research & Creative Works

First-principles full potential linear muffin-tin orbital-generalized gradient approximation electronic structure calculations of the new medium-Tc superconductor (MTSC) MgB2 and related diborides indicate that superconductivity in these compounds is related to the existence of Px,y-band holes at the γ point. Based on these calculations, we explain the absence of medium-Tc superconductivity for BeB2, AlB2, ScB2, and YB2. The simulation of a number of MgB2-based ternary systems using a supercell approach demonstrates that (i) the electron doping of MgB2 (i.e., MgB2-yXy with X=Be, C ...


Electron Self-Energy For The K And L Shells At Low Nuclear Charge, Ulrich D. Jentschura, Peter J. Mohr, Gerhard Soff Apr 2001

Electron Self-Energy For The K And L Shells At Low Nuclear Charge, Ulrich D. Jentschura, Peter J. Mohr, Gerhard Soff

Physics Faculty Research & Creative Works

A nonperturbative numerical evaluation of the one-photon electron self-energy for the K- and L-shell states of hydrogenlike ions with nuclear charge numbers Z =1 to 5 is described. Our calculation for the 1S1/2 state has a numerical uncertainty of 0.8 Hz in atomic hydrogen, and for the L-shell states (2S1/2 , 2P1/2 , and 2P3/2) the numerical uncertainty is 1.0 Hz. The method of evaluation for the ground state and for the excited states is described in detail. The numerical results are compared to results based on known terms in the expansion ...


Open Strings, 2d Gravity, And Ads/Cft Correspondence, Mariano Cadoni, Marco Cavaglia Mar 2001

Open Strings, 2d Gravity, And Ads/Cft Correspondence, Mariano Cadoni, Marco Cavaglia

Physics Faculty Research & Creative Works

We present a detailed discussion of the duality between dilaton gravity on AdS2 and open strings. The correspondence between the two theories is established using their symmetries and field theoretical, thermodynamic, and statistical arguments. We use the dual conformai field theory to describe two-dimensional black holes. In particular, all the semiclassical features of the black holes, including the entropy, have a natural interpretation in terms of the dual microscopic conformai dynamics. The previous results are discussed in the general framework of the anti-de Sitter/conformal field theory dualities.


Non-Sequential Double Ionization Of Ne In Intense Laser Pulses: A Coincidence Experiment, Robert Moshammer, Bernold Feuerstein, Daniel Fischer, Alexander Dorn, Claus Dieter Schroter, J. Deipenwisch, Jose R. Crespo Lopez-Urrutia, C. Hohr, Paul B. Neumayer, Joachim Hermann Ullrich, Horst Rottke, Christoph Trump, M. Wittmann, Georg Korn, Wolfgang Sandner Mar 2001

Non-Sequential Double Ionization Of Ne In Intense Laser Pulses: A Coincidence Experiment, Robert Moshammer, Bernold Feuerstein, Daniel Fischer, Alexander Dorn, Claus Dieter Schroter, J. Deipenwisch, Jose R. Crespo Lopez-Urrutia, C. Hohr, Paul B. Neumayer, Joachim Hermann Ullrich, Horst Rottke, Christoph Trump, M. Wittmann, Georg Korn, Wolfgang Sandner

Physics Faculty Research & Creative Works

The dynamics of Neon double ionization by 25 fs, 1.0 PW/cm2 laser pulses at 795 nm has been studied in a many particle coincidence experiment. The momentum vectors of all ejected atomic fragments (electrons and ions) have been measured using combined electron and recoil-ion momentum spectroscopy. Electron emission spectra for double and single ionization will be discussed. In both processes the mean electron energies differ considerably and high energetic electrons with energies of more than 120 eV have been observed for double ionization. The experimental results are in qualitative agreement with the rescattering model.


Fully Differential Cusp Electron Production Cross Sections For 75-Kev H₂⁺ + He Collisions, L. An, Kh Khayvat, Michael Schulz Feb 2001

Fully Differential Cusp Electron Production Cross Sections For 75-Kev H₂⁺ + He Collisions, L. An, Kh Khayvat, Michael Schulz

Physics Faculty Research & Creative Works

A kinematically complete experiment on single ionization for 75-keV H2+ + H e collisions was performed by measuring the fully momentum analyzed projectiles and recoil ions in coincidence. The electron momentum was deduced from momentum conservation. Clear signatures of the postcollision interaction between the outgoing projectiles and the electrons were observed in the momentum spectra of all collision products simultaneously.


Two-Dimensional Black Holes As Open Strings: A New Realization Of The Ads/Cft Correspondence, Mariano Cadoni, Marco Cavaglia Feb 2001

Two-Dimensional Black Holes As Open Strings: A New Realization Of The Ads/Cft Correspondence, Mariano Cadoni, Marco Cavaglia

Physics Faculty Research & Creative Works

We show that weak-coupled two-dimensional dilation gravity on anti-de Sitter space can be described by the dynamics of an open string. Neumann and Dirichlet boundary conditions for the string lead two different realizations of the anti-de Sitter/Conformal Field Theory correspondence. In particular, in the Dirichlet case the thermodynamical entropy of two-dimensional black holes can be exactly reproduced by counting the string states.


Electronic Structures And Magnetism Of Lani₅₋ₓFeₓ Compounds, Jinbo Yang, Chiu-Ying Tai, G. K. Marasinghe, George Daniel Waddill, Oran Allan Pringle, William Joseph James Jan 2001

Electronic Structures And Magnetism Of Lani₅₋ₓFeₓ Compounds, Jinbo Yang, Chiu-Ying Tai, G. K. Marasinghe, George Daniel Waddill, Oran Allan Pringle, William Joseph James

Physics Faculty Research & Creative Works

A systematic study of the magnetic moments and hyperfine interactions of the LaNi5-xFex compounds was performed using the spin-polarized tight-binding-linear-muffin-tin-orbital methods (TBLMTO). The calculated results were compared with neutron diffraction and Mössbauer experimental data and found to be in good agreement. Fe atoms exhibit more localized magnetic moments in LaNi5-xFex when the Fe content x is lower than 1.0. The calculated magnetic moments of the Fe atoms approach values as large as 2.5μB due to the dilution effect. The strong s-d hybridization between the Ni and La atoms and the neighboring ...


Electric Field Controlled, Pulsed Autoionization In Two Electron Wave Packets, J. Greg Story, Heider N. Ereifej Jan 2001

Electric Field Controlled, Pulsed Autoionization In Two Electron Wave Packets, J. Greg Story, Heider N. Ereifej

Physics Faculty Research & Creative Works

In this paper, control of the evolution of a two electron wave packet through the application of a static electric field is demonstrated. Specifically, application of a small electric field is used to produce pulsed autoionization events, the timing of which can be controlled on a picosecond time scale. The technique is demonstrated by exciting calcium atoms using a short-pulsed laser to the 4p3/219d doubly excited state, which is energy degenerate with the 4p1/2nk stark states. Evolution of the resultant wave packet is monitored through the application of a second short laser pulse, which ...


Structural, Electronic, And Magnetic Properties Of Lani₅₋ₓTₓ (T = Fe, Mn) Compounds, Jinbo Yang, Chiu-Ying Tai, G. K. Marasinghe, George Daniel Waddill, Oran Allan Pringle, William Joseph James, Y. Kong Jan 2001

Structural, Electronic, And Magnetic Properties Of Lani₅₋ₓTₓ (T = Fe, Mn) Compounds, Jinbo Yang, Chiu-Ying Tai, G. K. Marasinghe, George Daniel Waddill, Oran Allan Pringle, William Joseph James, Y. Kong

Physics Faculty Research & Creative Works

Structures and magnetic properties of the LaNi5-xFex and LaNi5-xMnx compounds have been investigated using neutron diffraction and first-principles tight-binding-linear-muffin-tin-orbital methods. Both neutron diffraction refinement data and total energy calculations show that the Fe and Mn atoms preferentially occupy the 3g sites in the hexagonal CaCu5-type structure. The calculated magnetic moments of Fe and Ni atoms are of 2.4-2.5μB and 0.2-0.5μB in LaNi5-xFex, respectively. The magnetic structure exhibits more localized moments at Fe atoms in LaNi5-xFex when x ≤ 1.0. Electronic ...