Physical Sciences and Mathematics Commons^™

Composition-Dependent Oxygen Vacancy Formation In Multicomponent Wide-Band-Gap Oxides, Altynbek Murat, Julia E. Medvedeva

Physics Faculty Research & Creative Works

The formation and distribution of oxygen vacancy in layered multicomponent InAMO ₄ oxides with A3 ⁺=Al or Ga and M2 ⁺=Ca or Zn and in the corresponding binary oxide constituents is investigated using first-principles density functional calculations. Comparing the calculated formation energies of the oxygen defect at six different site locations within the structurally and chemically distinct layers of InAMO ₄ oxides, we find that the vacancy distribution is significantly affected not only by the strength of the metal-oxygen bonding, but also by the cation's ability to adjust to anisotropic oxygen environment created by the vacancy. In particular, …

Projectile Coherence Effects In Electron Capture By Protons Colliding With H₂ And He, Sachin D. Sharma, Ahmad Hasan, Kisra N. Egodapitiya, T. P. Arthanayaka, G. Sakhelashvili, Michael Schulz

Physics Faculty Research & Creative Works

We have measured differential cross sections for single and dissociative capture for 25 and 75 keV protons colliding with H₂ and He. Significant differences were found depending on whether the projectile beam was coherent or incoherent. For 75 keV p+H₂ these differences can be mostly associated with molecular two-center interference and possibly some contributions from path interference. For 25 keV (both targets) they are mostly due to path interference between different impact parameters leading to the same scattering angles and, for the H₂ target, possibly some contributions from molecular two-center interference.

Erratum: Triple Compton Effect: A Photon Splitting Into Three Upon Collision With A Free Electron (Physical Review Letters (2012) 108 (233201)), Erik Loetstedt, Ulrich D. Jentschura

Physics Faculty Research & Creative Works

No abstract provided.

Low Energy (E, 2e) Study From The 1t₂ Orbital Of Ch₄, Shenyue Xu, Hari Chaluvadi, Xueguang Ren, Thomas Pfluger, Arne Senftleben, Chuangang Ning, Shuncheng Yan, Peng Zhang, Jie Yang, Xinwen Ma, Joachim Hermann Ullrich, Don H. Madison, Alexander Dorn

Physics Faculty Research & Creative Works

Single ionization of the methane (CH₄) 1t₂ orbital by 54 eV electron impact has been studied experimentally and theoretically. The measured triple differential cross sections cover nearly a 4π solid angle for the emission of low energy electrons and a range of projectile scattering angles. Experimental data are compared with theoretical calculations from the distorted wave Born approximation and the molecular three-body distorted wave models. It is found that theory can give a proper description of the main features of experimental cross section only at smaller scattering angles. For larger scattering angles, significant discrepancies between experiment and …

Fully Differential Cross Section For Four Body Charge Transfer Process, Uttam Chowdhury, Allison L. Harris, Jerry Peacher, Don H. Madison

Physics Faculty Research & Creative Works

Recently experimental fully differential cross sections (FDCS) have been reported for double capture in proton helium collisions which disagree with existing theoretical calculations by two orders of magnitude. We introduce here a theoretical model for charge transfer processes which is fully quantum mechanical and takes all post collision interactions (PCI) between the particles into account exactly. The results of this model are in much better agreement with experimental data.

Implications For The Origin Of Grb 051103 From Ligo Observations, J. Abadie, Marco Cavaglia, For Full List Of Authors, See Publisher's Website.

Physics Faculty Research & Creative Works

We present the results of a LIGO search for gravitational waves (GWs) associated with GRB 051103, a short-duration hard-spectrum gamma-ray burst (GRB) whose electromagnetically determined sky position is coincident with the spiral galaxy M81, which is 3.6 Mpc from Earth. Possible progenitors for short-hard GRBs include compact object mergers and soft gamma repeater (SGR) giant flares. A merger progenitor would produce a characteristic GW signal that should be detectable at a distance of M81, while GW emission from an SGR is not expected to be detectable at that distance. We found no evidence of a GW signal associated with GRB …

Conditions For Extracting Photoionization Cross Sections From Laser-Induced High-Order-Harmonic Spectra, Guoli Wang, Cheng Jin, Anh-Thu Le, C. D. Lin

Physics Faculty Research & Creative Works

We show that photoionization cross sections of atoms can be accurately extracted from the high-order-harmonic spectra generated by intense infrared lasers only if the degree of ionization in the gas medium is small, implying that for this purpose the high-order-harmonic generation spectra should be taken at low gas pressure and at low laser intensity experimentally.

Four Body Charge Transfer Process In Proton Helium Collision, Uttam Chowdhury, Allison L. Harris, Jerry Peacher, Don H. Madison

Physics Faculty Research & Creative Works

Recent advancements in experimental techniques now allow for the study of fully differential cross sections for 4-body collisions. Theoretical fully differential cross sections will be presented and compared with absolute experimental data for transfer-excitation in proton-helium collisions. The role of different scattering mechanism will be discussed.

Polarization Transfer Of Bremsstrahlung Arising From Spin-Polarized Electrons, R. Märtin, G. Weber, R. Barday, Y. Fritzsche, U. Spillmann, W. Chen, R. D. Dubois, J. Enders, M. Hegewald, S. Hess, A. Surzhykov, D. B. Thorn, S. Trotsenko, M. Wagner

Physics Faculty Research & Creative Works

We report on a study of the polarization transfer between transversely polarized incident electrons and the emitted x rays for electron-atom bremsstrahlung. by means of Compton polarimetry we performed for the first time an energy-differential measurement of the complete properties of bremsstrahlung emission related to linear polarization, i.e., the degree of linear polarization as well as the orientation of the polarization axis. for the high-energy end of the bremsstrahlung continuum the experimental results for both observables show a high sensitivity on the initial electron spin polarization and prove that the polarization orientation is virtually independent of the photon energy. © …

Upper Limits On A Stochastic Gravitational-Wave Background Using Ligo And Virgo Interferometers At 600-1000 Hz, J. Abadie, Marco Cavaglia, For Full List Of Authors, See Publisher's Website.

Physics Faculty Research & Creative Works

A stochastic background of gravitational waves is expected to arise from a superposition of many incoherent sources of gravitational waves, of either cosmological or astrophysical origin. This background is a target for the current generation of ground-based detectors. In this article we present the first joint search for a stochastic background using data from the LIGO and Virgo interferometers. In a frequency band of 600-1000 Hz, we obtained a 95% upper limit on the amplitude of Ω_GW(f) = Ω₃(f/900Hz)³, of Ω₃ < 0.32, assuming a value of the Hubble parameter of h₁₀₀ = 0.71. These new limits are a …

Triple Compton Effect: A Photon Splitting Into Three Upon Collision With A Free Electron, Erik Loetstedt, Ulrich D. Jentschura

Physics Faculty Research & Creative Works

The process in which a photon splits into three after the collision with a free electron (triple Compton effect) is the most basic process for the generation of a high-energy multiparticle entangled state composed out of elementary quanta. The cross section of the process is evaluated in two experimentally realizable situations, one employing gamma photons and stationary electrons, and the other using keV photons and GeV electrons of an x-ray free electron laser. For the first case, our calculation is in agreement with the only available measurement of the differential cross section for the process under study. Our estimates indicate …

All-Sky Search For Gravitational-Wave Bursts In The Second Joint Ligo-Virgo Run, J. Abadie, Marco Cavaglia, For Full List Of Authors, See Publisher's Website.

Physics Faculty Research & Creative Works

We present results from a search for gravitational-wave bursts in the data collected by the LIGO and Virgo detectors between July 7, 2009 and October 20, 2010: data are analyzed when at least two of the three LIGO-Virgo detectors are in coincident operation, with a total observation time of 207 days. The analysis searches for transients of duration ≲ 1 s over the frequency band 64-5000 Hz, without other assumptions on the signal waveform, polarization, direction or occurrence time. All identified events are consistent with the expected accidental background. We set frequentist upper limits on the rate of gravitational-wave bursts …

Disorder Promotes Ferromagnetism: Rounding Of The Quantum Phase Transition In Sr₁₋ₓcaₓruo₃, Laszlo Demko, Sandor Bordacs, Thomas Vojta, David Nozadze, Fawaz Hrahsheh, Christopher Svoboda, Balazs Dora, Hiroyuki Yamada, Masashi Kawasaki, Yoshinori Tokura, Istvan Kezsmarki

Physics Faculty Research & Creative Works

The subtle interplay of randomness and quantum fluctuations at low temperatures gives rise to a plethora of unconventional phenomena in systems ranging from quantum magnets and correlated electron materials to ultracold atomic gases. Particularly strong disorder effects have been predicted to occur at zero-temperature quantum phase transitions. Here, we demonstrate that the composition-driven ferromagnetic-to-paramagnetic quantum phase transition in Sr_1-xCa_xRuO₃ is completely destroyed by the disorder introduced via the different ionic radii of the randomly distributed Sr and Ca ions. Using a magneto-optical technique, we map the magnetic phase diagram in the composition-temperature space. We find …

Dissipation Effects In Random Transverse-Field Ising Chains, Jose A. Hoyos, Thomas Vojta

Physics Faculty Research & Creative Works

We study the effects of Ohmic, super-Ohmic, and sub-Ohmic dissipation on the zero-temperature quantum phase transition in the random transverse-field Ising chain by means of an (asymptotically exact) analytical strong-disorder renormalization-group approach. We find that Ohmic damping destabilizes the infinite-randomness critical point and the associated quantum Griffiths singularities of the dissipationless system. The quantum dynamics of large magnetic clusters freezes completely, which destroys the sharp phase transition by smearing. The effects of sub-Ohmic dissipation are similar and also lead to a smeared transition. In contrast, super-Ohmic damping is an irrelevant perturbation; the critical behavior is thus identical to that of …

First Low-Latency Ligo+Virgo Search For Binary Inspirals And Their Electromagnetic Counterparts, J. Abadie, Marco Cavaglia, For Full List Of Authors, See Publisher's Website.

Physics Faculty Research & Creative Works

Aims. The detection and measurement of gravitational-waves from coalescing neutron-star binary systems is an important science goal for ground-based gravitational-wave detectors. In addition to emitting gravitational-waves at frequencies that span the most sensitive bands of the LIGO and Virgo detectors, these sources are also amongst the most likely to produce an electromagnetic counterpart to the gravitational-wave emission. A joint detection of the gravitational-wave and electromagnetic signals would provide a powerful new probe for astronomy. Methods. During the period between September 19 and October 20, 2010, the first low-latency search for gravitational-waves from binary inspirals in LIGO and Virgo data was …

Search For Gravitational Waves From Intermediate Mass Binary Black Holes, J. Abadie, Marco Cavaglia, For Full List Of Authors, See Publisher's Website.

Physics Faculty Research & Creative Works

We present the results of a weakly modeled burst search for gravitational waves from mergers of nonspinning intermediate mass black holes in the total mass range 100-450M_⊙ and with the component mass ratios between 1:1 and 4:1. The search was conducted on data collected by the LIGO and Virgo detectors between November of 2005 and October of 2007. No plausible signals were observed by the search which constrains the astrophysical rates of the intermediate mass black holes mergers as a function of the component masses. In the most efficiently detected bin centered on 88 + 88 M_⊙, …

Quantum Griffiths Singularities In Ferromagnetic Metals, David Nozadze, Thomas Vojta

Physics Faculty Research & Creative Works

We present a theory of the quantum Griffiths phases associated with the ferromagnetic quantum phase transition in disordered metals. For Ising spin symmetry, we study the dynamics of a single rare region within the variational instanton approach. For Heisenberg symmetry, the dynamics of the rare region is studied using a renormalization group approach. In both cases, the rare region dynamics is even slower than in the usual quantum Griffiths case because the order parameter conservation of an itinerant ferromagnet hampers the relaxation of large magnetic clusters. The resulting quantum Griffiths singularities in ferromagnetic metals are stronger than power laws. For …

Electronic Properties Of Layered Multicomponent Wide-Band-Gap Oxides: A Combinatorial Approach, Altynbek Murat, Julia E. Medvedeva

Physics Faculty Research & Creative Works

The structural, electronic, and optical properties of 12 multicomponent oxides with layered structure RAMO ₄, where R3 ⁺ = In or Sc, A3 ⁺ = Al or Ga, and M2 ⁺ = Ca, Cd, Mg, or Zn, are investigated using first-principles density functional approach. The compositional complexity of RAMO ₄ leads to a wide range of band-gap values varying from 2.45 eV for InGaCdO ₄ to 6.29 eV for ScAlMgO ₄ as obtained from our self-consistent screened-exchange local density approximation calculations. Strikingly, despite the different band gaps in the oxide constituents, namely, 2-4 eV in CdO, In ₂O …

Search For Gravitational Waves From Low Mass Compact Binary Coalescence In Ligo's Sixth Science Run And Virgo's Science Runs 2 And 3, J. Abadie, Marco Cavaglia, For Full List Of Authors, See Publisher's Website.

Physics Faculty Research & Creative Works

We report on a search for gravitational waves from coalescing compact binaries using LIGO and Virgo observations between July 7, 2009, and October 20, 2010. We searched for signals from binaries with total mass between 2 and 25M_⊙ this includes binary neutron stars, binary black holes, and binaries consisting of a black hole and neutron star. The detectors were sensitive to systems up to 40 Mpc distant for binary neutron stars, and further for higher mass systems. No gravitational-wave signals were detected. We report upper limits on the rate of compact binary coalescence as a function of total …

Unconventional Rf Photoresponse From A Superconducting Spiral Resonator, Alexander P. Zhuravel, Cihan Kurter, Alexey V. Ustinov, Steven M. Anlage

Physics Faculty Research & Creative Works

Superconducting thin film resonators employing strip geometries show great promise in rf/microwave applications due to their low loss and compact nature. However, their functionality is limited by nonlinear effects at elevated rf/microwave powers. Here, we show that by using a planar spiral geometry carrying parallel currents in adjacent turns, this limitation can be minimized. We investigate the rf current distributions in spiral resonators implemented with Nb thin films via laser scanning microscopy. The rf current density profile along the width of the individual turns of the resonators reveals an unconventional trend: maximum current in the middle of the structure and …

Size Effect On The Structural, Magnetic, And Magnetotransport Properties Of Electron Doped Manganite La 0.15ca 0.85mno 3, Rini Thomas, Gangadhar Das, Rajib Mondal, R. Pradheesh, R. N. Mahato, T. Geetha Kumary, R. Nirmala, A. V. Morozkin, J. Lamsal, W. B. Yelon, A. K. Nigam, S. K. Malik

Physics Faculty Research & Creative Works

Nanocrystalline La_0.15Ca_0.85MnO₃ samples of various grain sizes ranging from ∼17 to 42 nm have been prepared by sol-gel technique. Phase purity and composition were verified by room temperature x-ray diffraction and SEM-EDAX analysis. the bulk La_0.15Ca_0.85MnO₃ is known to order antiferromagnetically around 170 K and to undergo a simultaneous crystal structural transition. DC magnetization measurements on 17 nm size La_0.15Ca_0.85MnO₃ show a peak at ∼130 K (T N) in zero-field-cooled (ZFC) state. Field-cooled magnetization bifurcates from ZFC data around 200 K hinting a weak ferromagnetic …

Charge Exchange And Ionization In N ⁷ ⁺, N 6 +, C 6 +H(N = 1, 2) Collisions Studied Systematically By Theoretical Approaches, K. Igenbergs, J. Schweinzer, A. Veiter, L. Perneczky, E. Frühwirth, M. Wallerberger, Ronald E. Olson, F. Aumayr

Physics Faculty Research & Creative Works

The introduction of gases like nitrogen or neon for cooling the edge region of magnetically confined fusion plasmas has triggered a renewed interest in state-selective cross sections necessary for plasma diagnostics by means of charge exchange recombination spectroscopy. to improve the quality of spectroscopic data analysis, charge exchange and ionization cross sections for N⁷⁺ + H (n = 1, 2) have been calculated using two different theoretical approaches, namely the atomic-orbital close-coupling method and the classical trajectory Monte Carlo method. Total and state-resolved charge exchange cross sections are presented in detail. in the second part, we compare two collision …

Doubly And Triply Differential Ionization Measurements Using Femtoamp Beams Of Positrons And Electrons, R. D. Dubois

Physics Faculty Research & Creative Works

Experimental methods and techniques being used to generate doubly and triply differential ionization data for positron and electron beams are discussed. It is shown that even for femtoamp, or smaller, beam intensities, highly detailed differential studies can be performed and differences resulting from kinematic effects due to the sign of the projectile can be identified. Examples using 250 eV impact ionization of molecular nitrogen are provided. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

Switching Nonlinearity In A Superconductor-Enhanced Metamaterial, Cihan Kurter, Philippe Tassin, Alexander P. Zhuravel, Lei Zhang, Thomas Koschny, Alexey V. Ustinov, Costas M. Soukoulis, Steven M. Anlage

Physics Faculty Research & Creative Works

We demonstrate a nonlinear metamaterial that can be switched between low and high transmission by controlling the power level of the incident beam. The origin of this nonlinear response is the superconducting Nb thin film employed in the metamaterial structure. We show that with moderate RF power of about 22 dBm it is possible to quench the superconducting state as a result of extremely strong current densities at the corners of the metamaterial's split-ring resonators. We measure a transmission contrast of 10 dB and a change in group delay of 70 ns between the low and high power states.

Observation Of Spin Glass State In Weakly Ferromagnetic Sr 2fecoo 6 Double Perovskite, R. Pradheesh, Harikrishnan S. Nair, C. M.N. Kumar, Jagat Lamsal, R. Nirmala, P. N. Santhosh, William B. Yelon, S. K. Malik, V. Sankaranarayanan, K. Sethupathi

Physics Faculty Research & Creative Works

A spin glass state is observed in the double perovskite oxide Sr₂FeCoO₆ prepared through sol-gel technique. Initial structural studies using x rays reveal that the compound crystallizes in tetragonal I4/m structure with lattice parameters, a 5.4609(2) Å and c 7.7113(7) Å. the temperature dependent powder x ray diffraction data reveal no structural phase transition in the temperature range 10-300 K. However, the unit cell volume shows an anomaly coinciding with the magnetic transition temperature thereby suggesting a close connection between lattice and magnetism. Neutron diffraction studies and subsequent bond valence sums analysis show that in Sr_{2 …}

Low-Energy Electron-Impact Ionization Of Argon: Three-Dimensional Cross Section, Xueguang Ren, Thomas Pfluger, Joachim Hermann Ullrich, Oleg I. Zatsarinny, Klaus Bartschat, Don H. Madison, Alexander Dorn

Physics Faculty Research & Creative Works

Low-energy (E ₀ = 70.8 eV) electron-impact single ionization of a 3p electron in argon has been studied experimentally and theoretically. Our measurements are performed using the so-called reaction microscope technique, which can cover nearly a full 4π solid angle for the emission of a secondary electron with energy below 15 eV and projectile scattering angles ranging from -8° to -30°. The measured cross sections are internormalized across all scattering angles and ejected energies. Several theoretical models were employed to predict the triple-differential cross sections (TDCSs). They include a standard distorted-wave Born approximation (DWBA), a modified version to account for …

Implementation And Testing Of The First Prompt Search For Gravitational Wave Transients With Electromagnetic Counterparts, J. Abadie, Marco Cavaglia, For Full List Of Authors, See Publisher's Website.

Physics Faculty Research & Creative Works

Aims. A transient astrophysical event observed in both gravitational wave (GW) and electromagnetic (EM) channels would yield rich scientific rewards. A first program initiating EM follow-ups to possible transient GW events has been developed and exercised by the LIGO and Virgo community in association with several partners. In this paper, we describe and evaluate the methods used to promptly identify and localize GW event candidates and to request images of targeted sky locations.

Methods. During two observing periods (Dec. 17, 2009 to Jan. 8, 2010 and Sep. 2 to Oct. 20, 2010), a low-latency analysis pipeline was used to identify …

Low Energy (E,2e) Measurements Of Ch⁴ And Neon In The Perpendicular Plane, Kate L. Nixon, Andrew James Murray, Hari Chaluvadi, Sadek Amami, Don H. Madison, Chuangang Ning

Physics Faculty Research & Creative Works

Low energy experimental and theoretical triple differential cross sections for the highest occupied molecular orbital of methane (1t₂) and for the 2p atomic orbital of neon are presented and compared. These targets are iso-electronic, each containing 10 electrons and the chosen orbital within each target has p-electron character. Observation of the differences and similarities of the cross sections for these two species hence gives insight into the different scattering mechanisms occurring for atomic and molecular targets. The experiments used perpendicular, symmetric kinematics with outgoing electron energies between 1.5 eV and 30 eV for CH₄ and 2.5 eV …

Bound-Free Pair Production In Ultra-Relativistic Ion Collisions At The Lhc Collider: Analytic Approach To The Total And Differential Cross Sections, Anton N. Artemyev, Ulrich D. Jentschura, Valery G. Serbo, Andrey S. Surzhykov

Physics Faculty Research & Creative Works

A theoretical investigation of the bound-free electron-positron pair production in relativistic heavy ion collisions is presented. Special attention is paid to the positrons emitted under large angles with respect to the beam direction. The measurement of these positrons in coincidence with the down-charged ions is in principle feasible by LHC experiments. In order to provide reliable estimates for such measurements, we employ the equivalent photon approximation together with the Sauter approach and derive simple analytic expressions for the differential pair-production cross section, which compare favorably to the results of available numerical calculations. Based on the analytic expressions, detailed calculations are …

State-Selective Electron Transfer And Ionization In Collisions Of Highly Charged Ions With Ground-State Na(3s) And Laser-Excited Na *(3p), I. Blank, Sebastian Otranto, C. Meinema, Ronald E. Olson, R. Hoekstra

Physics Faculty Research & Creative Works

Single electron transfer and ionization in collisions of N⁵⁺ and Ne⁸⁺ with ground state Na(3s) and laser excited Na *(3p) are investigated both experimentally and theoretically at collision energies from 1 to 10 keV/amu, which includes the classical orbital velocity of the valence electron. State-selective partial cross sections are obtained using recoil-ion momentum spectroscopy in combination with a magneto-optically cooled Na atom target. a strong dependence of the cross sections on the collision energy is observed. in general, both the relative magnitude and the energy dependence are found to be in good agreement with classical-trajectory Monte Carlo calculations. …