Physical Sciences and Mathematics Commons^™

Layer-Resolved Spin Polarization In Sb Overlayers On Nimnsb, Ralph Skomski, T. Komesu, C.N. Borca, H.-K. Jeong, Peter A. Dowben, D. Ristoiu, J.P. Nozie´Res

Peter Dowben Publications

The magnetism of antimony overlayers on a ferromagnetic substrate is investigated by spin-polarized inverse photoemission and explained in terms of a spin-dependent envelope-function approximation (SDEFA). The atomic structure of the films, which were deposited by sputtering Sb onto a NiMnSb(001) substrate, is characterized by a unique combination of three features: (i) NiMnSb is a highly spin-polarized semi-Heusler alloy predicted to be halfmetallic, (ii) antimony is a semimetal, exhibiting a band structure reminiscent of indirect-gap semiconductors, and (iii) the small lattice mismatch ensures a well-controlled interface. Combined x-ray absorption spectroscopy and spin-polarized inverse photoemission yield a layer-resolved spin polarization decaying on …

Transcribing Spacetime Data Into Matrices, Vatche Sahakian

All HMC Faculty Publications and Research

In certain supergravity backgrounds, D0 branes may polarize into higher dimensional Dp branes. We study this phenomenon in some generality from the perspective of a local inertial observer and explore polarization effects resulting from tidal-like forces. We find D2 brane droplets made of D0 branes at an extremum of the Born-Infeld action even in scenarios where the RR fields may be zero. These solutions lead us to a local formulation of the UV-IR correspondence. A holographic Planck scale bound on the number of D0 branes plays an important role in the analysis. We focus on the impact of higher order …

Fine Structure On The Green Band In Zno, D. C. Reynolds, David C. Look, B. Jogai

Physics Faculty Publications

An emission band at 2.4 eV, called the green band, is observed in most ZnO samples, no matter what growth technique is used. Sometimes this band includes fine structure, which consists mainly of doublets, repeated with a longitudinal-optical-phonon-energy spacing (72 meV). We have developed a vibronic model for the green band, based on transitions from two separate shallow donors to a deep acceptor. The donors, at energies 30 and 60 meV from the conduction-band edge, respectively, are also found from Hall-effect measurements.

Evidence For Shallow Acceptors In Gan, D. C. Reynolds, David C. Look, B. Jogai, Richard J. Molnar

Physics Faculty Publications

Two low-temperature photoluminescence lines in GaN, in the region of energies commonly interpreted as longitudinal optical-phonon replicas of free excitons, donor-bound excitons, or acceptor-bound excitons, are reinterpreted as acceptor-bound excitons (A⁰X’s) collapsing to n=2 and n=3 excited states, respectively, of the acceptors involved. Application of this model to two sets of A⁰X-related lines in hydride-vapor-phase-grown GaN gives acceptor energies of 85±1, and 115±1 meV, respectively. The existence of such shallow acceptor states, if confirmed, is of great technological importance.

The Role Of Interfaces In The Magnetoresistance Of Au/Fe/Au/Fe/Gaas(001), Axel Enders, T. L. Monchesky, Kenneth Myrtle, R. Urban, Brett Heinrich, Jurgen Kirschner, X.-G. Zhang, W. H. Butler

Axel Enders Publications

The electron transport and magnetoresistance (MR) were investigated in high quality crystalline epitaxial Fe(001) and Au(001) films and exchange coupled Au/Fe/Au/Fe/GaAs(001) trilayer structures. Fits to the experimental data were based on the semiclassical Boltzmann equation, which incorporates the electronic properties obtained from first-principles local density functional calculations. The fits require a surprisingly high asymmetry for the spin dependent electron lifetimes in Fe, τ^↓/ τ^↑ =10 at room temperature. Despite the large atomic terraces at the Au/vacuum and Fe/GaAs interfaces the scattering at the outer interfaces was found to be diffuse. The origin of MR in Au/Fe/Au/Fe/GaAs(001) structures …

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-T_c superconductor (MTSC) MgB₂ and related diborides indicate that superconductivity in these compounds is related to the existence of P_x,y-band holes at the γ point. Based on these calculations, we explain the absence of medium-T_c 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., MgB_2-yX_y with X=Be, …

Parity Violation In Neutron Resonances Of Antimony And Iodine, Y Matsuda, J D. Bowman, Bret E. Crawford, P P J. Delheij, T Haseyama, J N. Knudsen, L Y. Lowie, A Masaike, G E. Mitchell, S I. Penttila, H Postma, N R. Roberson, S J. Seestrom, E I. Sharapov, Sharon L. Stephenson, Y-F Yen, V W. Yuan

Physics and Astronomy Faculty Publications

Parity violation in p-wave neutron resonances of ¹²¹Sb, ¹²³Sb, and ¹²⁷I has been measured by transmission of a longitudinally polarized neutron beam through natural antimony and iodine targets. The measurements were performed at the pulsed spallation neutron source of the Los Alamos Neutron Science Center. Five statistically significant parity violation effects were observed in ¹²¹Sb, one effect in ¹²³Sb, and seven effects in ¹²⁷I. The weak interaction rms matrix elements and the corresponding spreading widths were determined.

Parity Violation In Neutron Resonances Of 117 Sn, D A. Smith, J D. Bowman, Bret E. Crawford, C A. Grossmann, T Haseyama, Mikkel B. Johnson, A Masaike, Y Matsuda, G E. Mitchell, V A. Nazarenko, S I. Penttila, N R. Roberson, S J. Seestrom, E I. Sharapov, L M. Smotritsky, Sharon L. Stephenson, S Tomsovic, V W. Yuan

Physics and Astronomy Faculty Publications

Parity nonconservation (PNC) has been studied in neutron p-wave resonances of ¹¹⁷Sn. The longitudinal asymmetries were measured for 29 p-wave resonances in the neutron energy range 0.8 eV to 1100 eV. Statistically significant PNC effects were observed for four resonances. A statistical analysis determined the rms weak mixing matrix element and the weak spreading width. A weak spreading width of Γ_w=(0.28_-0.15^+0.56)×10^-7 eV was obtained for¹¹⁷Sn.

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.

Meyer-Neldel Rule For Dark Current In Charge-Coupled Devices, Ralf Widenhorn, Lars Mündermann, Armin Rest, Erik Bodegom

Physics Faculty Publications and Presentations

We present the results of a systematic study of the dark current in each pixel of a charged-coupled device chip. It was found that the Arrhenius plot, at temperatures between 222 and 291 K, deviated from a linear behavior in the form of continuous bending. However, as a first approximation, the dark current, D, can be expressed as: D=Dₒ exp(−ΔE/kT),where ΔE is the activation energy, k is Boltzmann’s constant, and T the absolute temperature. It was found that ΔE and the exponential prefactor Dₒ follow the Meyer–Neldel rule (MNR) for all of the more than 222,000 investigated pixels. The isokinetic …

Single-Sided Noninvasive Inspection Of Multielement Sample Using Fan-Beam Multiplexed Compton Scatter Tomography, Matthew A. Lange

Theses and Dissertations

As aircraft age, corrosion forms upon unobservable surfaces, particularly at the junction of the sheet aluminum and the steel rivets used to attach the sheets to the airframe, degrading the aircraft s airworthiness. Previous research developed a noninvasive technique for the evaluation of the material composition of aluminum surfaces, utilizing the information encoded in the energy spectra of Compton-scattered gamma emissions. The spectra are gathered by a six-element, high purity germanium detector array. A, first principles, deterministic computer code is used to reconstruct a two-dimensional map of the electron density of aluminum samples. Previous efforts, to image pure aluminum samples, …

Time-Resolved Photoluminescence Of Inas/Gainsb Quantum Well Lasers, Michael R. Mckay

Theses and Dissertations

In the world of semiconductor photonic device fabrication, one important objective may be to extract as much light as possible from the device. In these devices, photons are created when electrons recombine with holes by transitioning from a high-energy state to a lower one. Unfortunately, electron-hole recombination does not always result in the formation of a photon. There are three basic types of recombination: the first results in the formation of a photon and is called radiative recombination; and the second and third, known as Shockley-Read-Hall and Auger recombination, result in the heating of the device and do not produce …

On The Effect Of Electron Plasma Waves With Relativistic Phase Velocity On Large-Angle Stimulated Raman Scattering Of Modulated Short Laser Pulse In Plasmas, Nikolai E. Andreev, Serguei Y. Kalmykov

Serge Youri Kalmykov

Suppression of a large-angle stimulated Raman scattering (LA-SRS) of a short modulated (two-frequency) laser pulse in a transparent plasma in the presence of a linear long-wavelength electron plasma wave (LW EPW) having relativistic phase velocity is considered under the conditions of weak and strong coupling. The laser spectrum includes two components with a frequency shift equal to the frequency of the LW EPW. The mutual influence of different spectral components of a laser on the SRS under a given angle in the presence of the LW EPW is examined.

Ultrathin Silicon Wafer Bonding Physics And Applications, Michael H. Beggans

Dissertations

Ultrathin silicon wafer bonding is an emerging process that simplifies device fabrication, reduces manufacturing costs, increases yield, and allows the realization of novel devices. Ultrathin silicon wafers are between 3 and 200 microns thick with all the same properties of the thicker silicon wafers (greater than 300 microns) normally used by the semiconductor electronics industry. Wafer bonding is one technique by which multiple layers are formed.

In this thesis, the history and practice of wafer bonding is described and applied to the manufacture of microelectomechanical systems (MEMS) devices with layer thickness on the scale of microns. Handling and processing problems …

Broadband Whole Package Fdtd Simulation, Shenjun Li

Dissertations

Whole package analysis is becoming more and more important with the rapid expansion of high frequency electronics. The motivation of this thesis is to find and implement a new method for broadband whole package simulation. 3-dimension (3-D) whole package Finite Difference Time Domain (FDTD) simulation result was first reported in detail in this thesis.

The FDTD method is a widely used full-wave time-domain simulation method used in the design and analysis for electromagnetic (EM) systems, such as antennas, wave propagating, and microwave circuits. Absorbing boundary condition (ABC), such as the perfect matched layer (PML) method, makes it possible to accurately …

Near-Field Imaging With Terahertz Pulses, Oleg Mitrofanov

Dissertations

High spatial resolution imaging is implemented with a novel collection mode near-field terahertz (THz) probe. Exceptional sensitivity of the probe allows imaging with spatial resolution of few microns using THz pulses with spectral content of 120 to 1500 microns. In the present study, the principle of the probe operation as well as the probe design and characteristics are described.

The probe performance is related to effective detection of radiation coupled into the probe aperture. Propagation of short single-cycle electromagnetic pulses through apertures as small as 1/300 of the wavelength is experimentally and numerically studied. Finite-difference time-domain method is used to …

Gated Multi-Cycle Integration (Gmci) For Focal Plane Array (Fpa) Applications, Haijiang Ou

Dissertations

In this thesis, the model and the theory of gated multi-cycle integration (GMCI) were first developed specifically for focal plane array dealing with repetitive or modulated image. The operational modes of GMCI include gated integration (GI), phase sensitive integration (PSI), multi-point summation, multi-point subtraction, multi-sample averaging and some of their combinations. Thus, the analytic theory of GMCI somehow unifies the theories of gated integration, phase sensitive detection, multiple summation and average. PSI works with background and/or dark current subtraction. As a result, the storage well of a pixel is mainly used for signal integration even if there exists a strong …

A Near-Infrared Filter System And Study Of Solar Umbral Dots At 1.6 Μm, Jingshan Wang

Dissertations

The observations of solar magnetic fields are very important because they influence events on the sun. Almost all of magnetographs in the world work in the visible wavelength and they are powerful instruments for measuring strong magnetic fields (above 1000 Gauss) on the sun. To measure the weak solar magnetic fields (below 1000 Gauss), a new filter system (magnetograph) working in near-IR wavelength has been developed in this work. This system includes an interference prefilter (FWHM - 40Å), a liquid crystal magnetic analyzer, a near-IR bireffingent filter (FWHM - 2.5Å), a near-IR Fabry-Perot filter (FWHM - 0.12Å), a near-IR InGaAs …

Software And Hardware Improvements For Digital Solar Magnetograph System, Shu Yang

Dissertations

Digital solar imaging systems have been widely used in solar observations. Their high resolution, high rate of image acquisition and convenience for off-line image processing have provided significant improvements to solar physics research. In this project, two digital magnetograph systems established at Big Bear Solar Observatory (BBSO) have been described. One is used to provide a high frame rate magnetogram system, and the other provides a real-time image alignment, i.e., a correlation tracker system.

The developed correlation tracker system consists of a high-speed 64x64 CCD camera, an EDT image grabbing board, an agile mirror, a D/A board and a Sun …

Quasi-Model-Independent Search For New Physics At Large Transverse Momentum, V. M. Abazov, Gregory R. Snow, D0 Collaboration

Gregory Snow Publications

We apply a quasi-model-independent strategy (“SLEUTH”) to search for new high p_T physics in ≈ 100 pb^-1 of pp̅ collisions at √s = 1.8 TeV collected by the DØ experiment during 1992–1996 at the Fermilab Tevatron. Over 32 eμX, W+jets-like, Z1jets-like, and (l/γ)(l/γ)(l/γ)X exclusive final states are systematically analyzed for hints of physics beyond the standard model. Simultaneous sensitivity to a variety of models predicting new phenomena at the electroweak scale is demonstrated by testing the method on a particular signature in each set of final states. No evidence of new high p_{T …}

Phonon-Pumped Terahertz Gain In N-Type Gaas/Algaas Superlattices, Greg Sun, Richard A. Soref

Physics Faculty Publications

Local population inversion and far-IR gain are proposed and theoretically analyzed for an unbiased n-doped GaAs/Al_0.15Ga_0.85As superlattice pumped solely by phonons. The lasing transition occurs at the Brillouin zone boundary of the superlattice wave vector k_zbetween the two conduction minibands CB1 and CB2 of the opposite curvature in k_zspace. The proposed waveguided structure is contacted above and below by heat sinks at 300 K and 77 K, respectively. Atop the superlattice, a heat buffer layer confines longitudinal optical phonons for enhanced optical-phonon pumping of CB1 electrons. A gain of 345 cm …

Exclusive Electroproduction Of Φ Mesons At 4.2 Gev, K Lukashin, E S. Smith, B Asavapibhop, R A. Hicks, D Lawrence, R Miskimen, Gerald Alvin Peterson, J Shaw

Gerald Alvin Peterson

We studied the exclusive reaction ep⃗e′p′φ using the φ⃗K+K- decay mode. The data were collected using a 4.2 GeV incident electron beam and the CEBAF Large Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator Facility. Our experiment covers the range in Q2 from 0.7 to 2.2 GeV2, and W from 2.0 to 2.6 GeV. Taken together with all previous data, we find a consistent picture of φ production on the proton. Our measurement shows the expected decrease of the t slope with the vector-meson formation time cΔτ below 2 fm. At 〈cΔτ〉=0.6 fm, we measure bφ=2.27±0.42 GeV-2. The cross …

Supernumerary Spacing Of Rainbows Produced By An Elliptical-Cross-Section Cylinder. Ii. Experiment, Charles L. Adler, David Phipps, Kirk W. Saunders, Justin K. Nash, James A. Lock

Physics Faculty Publications

We measured the supernumerary spacing parameter of the first- and second-order rainbows of two glass rods, each having an approximately elliptical cross section, as a function of the rod's rotation angle. We attribute large fluctuations in the supernumerary spacing parameter to small local inhomogeneities in the rod's refractive index. The low-pass filtered first-order rainbow experimental data agree with the prediction of ray-tracing-wave-front modeling to within a few percent, and the second-order rainbow data exhibit additional effects that are due to rod nonellipticity. (C) 2001 Optical Society of America.

Measurement Of Dijet Production In Neutral Current Deep Inelastic Scattering At High Q2 And Determination Of ΑS, J. Breitweg, S. Chekanov, M. Derrick, D. Krakauer, S. Magill, B. Musgrave, A. Pellegrino, J. Repond, R. Stanek, R. Yoshida, Margarita C. K. Mattingly, P. Antonioli, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, G. Cara Romeo, L. Cifarelli, F. Cindolo, A. Contin, M. Corradi, S. De Pasquale, P. Giusti, G. Iacobucci, G. Levi, A. Margotti, T. Massam, R. Nania, F. Palmonari

Faculty Publications

Dijet production has been studied in neutral current deep inelastic e+p scattering for 470 < Q2 < 20000 GeV2 with the ZEUS detector at HERA using an integrated luminosity of 38.4 pb-1. Dijet differential cross sections are presented in a kinematic region where both theoretical and experimental uncertainties are small. Next-to-leading-order (NLO) QCD calculations describe the measured differential cross sections well. A QCD analysis of the measured dijet fraction as a function of Q2 allows both a precise determination of αs(Mz) and a test of the energy-scale dependence of the strong coupling constant. A detailed analysis provides an improved estimate of the uncertainties of the NLO QCD cross sections arising from the paxton distribution functions of the proton. The value of αs(Mz), as determined from the QCD fit, is αs (MZ) = 0.1166 ± 0.0019(stat.)+0.0024-0.0044 (exp.) +0.00570.0044(th.). © 2001 Elsevier Science B.V.

Quantization Of Maximally Charged Slowly Moving Black Holes, George Siopsis

George Siopsis

We discuss the quantization of a system of slowly moving extreme Reissner-Nordström black holes. In the near-horizon limit, this system has been shown to possess an SL(2,R) conformal symmetry. However, the Hamiltonian appears to have no well-defined ground state. This problem can be circumvented by a redefinition of the Hamiltonian due to de Alfaro, Fubini, and Furlan (DFF). We apply the Faddeev-Popov quantization procedure to show that the Hamiltonian with no ground state corresponds to a gauge in which there is an obstruction at the singularities of moduli space requiring a modification of the quantization rules. The …

Quantization Of Maximally Charged Slowly Moving Black Holes, George Siopsis

Physics and Astronomy Publications and Other Works

We discuss the quantization of a system of slowly moving extreme Reissner-Nordström black holes. In the near-horizon limit, this system has been shown to possess an SL(2,R) conformal symmetry. However, the Hamiltonian appears to have no well-defined ground state. This problem can be circumvented by a redefinition of the Hamiltonian due to de Alfaro, Fubini, and Furlan (DFF). We apply the Faddeev-Popov quantization procedure to show that the Hamiltonian with no ground state corresponds to a gauge in which there is an obstruction at the singularities of moduli space requiring a modification of the quantization rules. The …

Phonon Modes In Inas Quantum Dots, Shang-Fen Ren, G Qin, Deyu Lu

Faculty publications – Physics

Phonon modes in spherical InAs quantum dots (QDs) with up to 11 855 atoms (about 8.5 nm in diameter) are calculated by using a valence force field model, and all the vibration frequencies and vibration amplitudes of the QDs are calculated directly from the lattice-dynamic matrix. The projection operators of the irreducible representations of the group theory are employed to reduce the computational intensity, which further allows us to investigate the quantum confinement effect of phonon modes with different symmetries. It is found that the size effects of phonon modes depend on the symmetry of the modes. For zinc-blende structure, …

Search For Neutral Supersymmetric Higgs Bosons In Pp̅ Collisions At √S = 1.8 Tev, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We present the results of a search for neutral Higgs bosons produced in association with b quarks in pp̅→ bb̅bb̅ final states with 91 ± 7 pb^-1 of pp̅ collisions at √s =1.8 TeV recorded by the Collider Detector at Fermilab. We find no evidence of such a signal and the data are interpreted in the context of the neutral Higgs sector of the minimal supersymmetric extension of the standard model. With basic parameter choices for the supersymmetric scale and the stop-quark mixing, we derive 95% C.L. lower mass limits for neutral Higgs bosons for tanb values …

Quantum-Mechanical Analysis Of A Longitudinal Stern-Gerlach Effect, Gordon A. Gallup, Herman Batelaan, Timothy J. Gay

Gordon Gallup Publications

We present the results of a rigorous quantum-mechanical calculation of the propagation of electrons through an inhomogeneous magnetic field with axial symmetry. A complete spin polarization of the beam is demonstrated assuming that a Landau eigenstate can be inserted into the field. This is in contrast with the semiclassical situation, where the spin splitting is blurred.

Investigation Of The Structure Of T He Ternary Cluster Of Aniline−Water−Tetrahydrofuran And Its Cation By Infrared Depletion Spectroscopy, Taisuke Nakanaga, Naveed Piracha, Fumiyuki Ito

Naveed K. Piracha

No abstract provided.