Showing papers by "John B Ketterson published in 2004"
TL;DR: In this paper, the authors synthesized two chalcopyrite compounds: MnGeP2 and MnGeAs2, which are indirect semiconductors with band gaps of 0.24 and 0.06 eV, respectively.
49 citations
TL;DR: In this paper, Rivkin et al. proposed a method to solve the problem of particle filtering in the context of physics and astronomy at the University of Northwestern University, Chicago, Illinois, USA.
Abstract: K. Rivkin,1 A. Heifetz,2 P. R. Sievert,1 and J. B. Ketterson1,2 1Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Avenue, Evanston, Illinois 60208, USA 2Department of Electrical and Computer Engineering, Northwestern University, 2145 Sheridan Avenue, Evanston, Illinois 60208, USA (Received 13 January 2004; revised manuscript received 18 May 2004; published 8 November 2004)
39 citations
TL;DR: In this article, a large shift of the uniform mode from 1200 to 1800 Oe, and a dramatic decrease in its intensity are observed as Di increases from 0 to 300 nm.
Abstract: Square lattices of permalloy rings with different inner diameters (Di) were fabricated by electron beam lithography and investigated by ferromagnetic resonance (FMR). Results reveal that FMR spectra are sensitive to the ring dimensions. A large shift of the uniform mode from 1200 to 1800 Oe, and a dramatic decrease in its intensity are observed as Di increases from 0 to 300 nm. Other resonance peaks at fields slightly below the uniform mode greatly increase in intensity and shift to lower field with increasing Di. An isolated resonance below 200 Oe is also observed. Possible reasons for these variations are discussed.
31 citations
TL;DR: The crystal structure of MnSnAs2 is chalcopyrites, which are related to the more familiar tetrahedrally-coordinated zinc-blende materials, with lattice constants of a = 5794 A, c = 11365 A.
Abstract: We have synthesized MnSnAs2 single crystals using the vertical temperature gradient solidification method The crystal structure of MnSnAs2 is chalcopyrites, which are “genealogically” related to the more familiar tetrahedrally-coordinated zinc-blende materials, with lattice constants of a = 5794 A, c = 11365 A Using the experimentally determined lattice constants and crystal structure, we carried out first principles electronic structure calculations, using the full-potential linearized augmented plane wave (FLAPW) method in the local density approximation (LDA) The lowest total energies were observed for the AFM state, indicating that AFM ordering in the system is energetically favored at 0 K We find that MnSnAs2 is metallic in the electronic calculation Interestingly, MnSnAs2 exhibited ferromagnetism with TC = 328 K (© 2004 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim)
14 citations
TL;DR: In this paper, structural and thermoelectric properties of (Sb1-xBix)2Te3 thin films on CdTe(111)B have been investigated.
Abstract: We have investigated the structural and thermoelectric properties of (Sb1-xBix)2Te3 thin films on CdTe(111)B. Analysis of X-ray diffraction patterns (θ–2θ scans and rocking curves) of the films shows that they are of high quality and that they are well aligned with their (00.1) axis normal to the substrates. Measurements of the temperature-dependent thermoelectric power, resistivity, and Hall coefficient of the films were performed with respect to the binary composition, x. For the samples in the range 0.2
13 citations
TL;DR: In this paper, the magnetic anisotropy is strongly dependent on the surface reconstruction of GaAs(001) substrates and the increase of the periodicity from 5nm ∕5nm to 10nm∕10nm also changes the magnetic aisotropic.
Abstract: Epitaxial hybrid structures of the ferromagnet–semiconductor superlattice MnAs∕GaAs were grown on GaAs(001) substrates by molecular-beam epitaxy and the dependence of the magnetic properties on the growth temperature and the periodicity were characterized. The magnetic anisotropy is strongly dependent on the surface reconstruction of GaAs(001) substrates. The increase of the periodicity from 5nm∕5nm to 10nm∕10nm also changes the magnetic anisotropy. These results demonstrate that the surface reconstruction of the substrate and the periodicity determine the magnetic structure of the MnAs∕GaAs superlattices.Epitaxial hybrid structures of the ferromagnet–semiconductor superlattice MnAs∕GaAs were grown on GaAs(001) substrates by molecular-beam epitaxy and the dependence of the magnetic properties on the growth temperature and the periodicity were characterized. The magnetic anisotropy is strongly dependent on the surface reconstruction of GaAs(001) substrates. The increase of the periodicity from 5nm∕5nm to 10nm∕10nm also changes the magnetic anisotropy. These results demonstrate that the surface reconstruction of the substrate and the periodicity determine the magnetic structure of the MnAs∕GaAs superlattices.
10 citations
TL;DR: In this article, the photoluminescence from polycrystalline ZnO films deposited on sapphire was studied as a function of the in situ oxygen pressure during growth and ex situ annealing.
7 citations
TL;DR: In this article, an enhancement of both Tc and the magnetic anisotropy, as well as unusual electrical transport properties, are observed in superlattice thin films consisting of metallic ferromagnet MnAs and semiconducting GaAs.
Abstract: An enhancement of both Tc and the magnetic anisotropy, as well as unusual electrical transport properties, are observed in superlattice thin films consisting of metallic ferromagnet MnAs and semiconducting GaAs. Structural analysis indicates that the MnAs layer is hexagonal rather than zinc blende. All films studied display room temperature ferromagnetism with a Tc higher than that of a single-layer MnAs film. A MnAs(5 nm)/GaAs(5 nm) superlattice showed the highest Tc (345 K) and the largest magnetic anisotropy. Furthermore, the temperature-dependent resistance of this sample shows semiconductor-like behavior and exhibited negative magnetoresistance, suggesting an interplay between the charge carriers and localized magnetic ions.
6 citations
Book•
01 Jan 2004
TL;DR: In this article, the authors present an overview of the history of superconductivity in high-temperature superconductors and their application in the field of superfluid 3He and Cuprate Superconductors.
Abstract: 1 Recent Developments.- 2 Nanostructured Superconductors.- 3 Proximity-Coupled Systems: Quasiclassical Theory of Superconductivity.- 4 Universal Properties of Cuprate Superconductors: Evidence and Implications.- 5 Photoemission in the High-Tc Superconductors.- 6 Concepts in High Temperature Superconductivity.- 7 Organic Superconductors.- 8 Unconventional Superconductivity in Novel Materials.- 9 Electronic Theory for Superconductivity in High-Tc, Cuprates and Sr2Ru04.- 10 Heavy Fermion Superconductivity.- 11 Superfluid 3He and the Cuprate Superconductors.- Author Index.- of Volume I.- History of Superconductivity.- K. H. Bennemann, J . B. Ketterson.- 1.1 Introduction.- 1.2 High Transition-Temperature Superconductivity and Novel Superconductors.- 1.3 Summary.- 2 Theoretical Foundation: Phenomenology and Microscopic Theory.- L. Pitaevskii.- 2.1 Non-Diagonal Long Range Order and Superfluidity.- 2.2 Non-Diagonal Long Range Order in Superconductors.- 2.3 London Equation.- 2.4 Thermodynamics of Superconductors in a Magnetic Field.- 2.5 The Intermediate State of Superconductors.- 2.6 The Ginzburg-Landau Theory.- 2.7 Surface Energy at the Boundary Between Normal and Superconducting Phases.- 2.8 Superconductors of the Second Kind.- 2.9 Quantized Vortex Lines.- 2.10 Vortex-Vortex Interactions.- 2.11 Cooper-Pairing.- 2.12 Energy Spectrum of a Superconductor.- 2.13 Thermodynamic Properties of Superconductors.- 2.14 Elements of the Theory of Green's Functions.- 2.15 Green's Function of a Superconductor.- 2.16 Temperature Green's Functions.- 2.17 Temperature Green's Functions of a Superconductor.- 3 Fluctuation Phenomena in Superconductors.- A. 1. Larkin, A. A. Varlamov.- 3.1 Introduction.- 3.2 Ginzburg-Landau Formalism : Thermodynamics.- 3.3 Fluctuations Below the Critical Temperature.- 3.4 Ginzburg-Landau Theory of Fluctuations in Transport Phenomena.- 3.5 Fluctuations Near S-I Transition.- 3.6 Microscopic Derivation of the TDGL Equation.- 3.7 Fluctuation Conductivity.- 3.8 Manifestation of Fluctuations in Various Properties.- 3.9 Conclusions.- 4 Electron-Phonon Superconductivity.- F . Marsiglio, J. P. Carbotte.- 4.1 Introduction.- 4.2 The Electron-Phonon Interaction: Overview.- 4.3 The Phonons.- 4.4 The Critical Temperature and the Energy Gap.- 4.5 Thermodynamics and Critical Magnetic Fields.- 4.6 Response Functions.- 4.7 Summary.- 4.8 Appendix: Microscopic Developments.- 5 Theory of Superconducting Alloys.- L. P. Gor'kov.- 5.1 Introduction.- 5.2 Averages of Green Functions Over Impurities.- 5.3 Superconducting Alloys with a Small Gap.- 5.4 Paramagnetic Alloys and Gapless Superconductivity.- 5.5 Eilenberger Equations.- 5.6 Final Remark.- H. R. Ott.- 6.1 Introduction.- 6.2 Typical Structural Characteristics.- 6.3 Occurrence of Superconductivity.- 6.4 Physical Properties of Copper Oxides.- 6.6 Final Remarks.- 7 Spin Fluctuation Model for d-wave Superconductivity.- A. V. Chubukov, D. Pines, and J. Schmalian.- 7.1 Introduction and Overview.- 7.2 Spin-Fermion Model.- 7.3 Summary of Strong-Coupling Theory for Electron-Phonon Pairing.- 7.4 Strong-Coupling Approach to Spin-Fermion Interaction.- 7.5 Fingerprints of Spin Fermion Pairing.- 7.6 Comparison with the Experiments on Cuprates.- 7.7 Conclusions.- 8 Tunneling Spectroscopy of Conventional and Unconventional Superconductors.- J . Zasadzinski.- 8.1 Introduction.- 8.2 Basic Tunneling Phenomenology.- 8.3 Tunneling and Strong-Coupling Effects: Microscopic Picture.- 8.4 Tunneling Spectroscopy of Conventional Superconductors.- 8.5 Tunneling in High-Temperature Superconductors.- 8.6 Heavy Fermion Sup erconductors.- 8.7 Organic Superconductors.- 8.8 Other Materials.- 8.9 Conclusions.- 9 Pairing Symmetry in Cuprate Superconductors: Phase-Sensitive Tests.- C. C. Tsuei, J. R. Kirtley.- 9.1 Introduction.- 9.2 Phase-Sensitive Tests: Theoretical Background.- 9.3 Phase-Sensitive Tests: Experiments.- 9.4 Universality of t he d-Wave Pair State.- 9.5 Implications of d-Wave Pairing Symmetry.- 9.6 Conclusions.- 10 Vortex Matter.- G. Blatter, V. B. Geshkenbein.- 10.1 Introduction.- 10.2 Ginzburg-Landau- and London Theories.- 10.3 Vortex Lines.- 10.4 Vortex Lattice.- 10.5 Layered Materials.- 10.6 Anisotropic Scaling Theory.- 10.7 Statistical Mechanics.- 10.8 Quenched Disorder : Pinning and Creep.- 10.9 Uncorrelated Disorder: Collective Pinning and Creep.- 10.10 Correlated Disorder.- 10.11 Surface- and Geometrical Barriers.- 10.12 Vortex Glasses.- 10.1 3 Concluding Remarks.
5 citations
TL;DR: In this paper, an image-intensified charge-coupled-device (ICCD) version of Z-scan was presented by employing an ICCD detector and fixing the sample at the beam waist, and a measurement of the third-order nonlinear optical coefficient of single crystal zinc oxide (ZnO).
Abstract: We present an image-intensified charge-coupled-device (ICCD) version of Z-scan by employing an ICCD detector and fixing the sample at the beam waist, and a measurement of the third-order nonlinear optical coefficient of single crystal zinc oxide (ZnO). The χ(3) value of −9.1×10−15 cm2/W measured is in agreement with the published result. Our Z-scan configuration of placing sample at beam waist and collecting the whole wavefront by an ICCD detector is simple and can be deployed in cryogenic research where the sample cannot be Z-scanned.
3 citations
TL;DR: In this paper, a GaAs/Ge multilayer structure successfully fabricated using molecular beam epitaxy was grown on (001) GaAs substrates at a growth temperature of 580 °C.
Abstract: MnAs/Ge multilayer structures successfully fabricated using molecular beam epitaxy were grown on (001) GaAs substrates at a growth temperature of 580 °C. The multilayer with a 100 A period thickness exhibited ferromagnetism up to 345 K with a coercive field of 147 Oe at 300 K and a vanishingly small in-plane magnetic anisotropy, as determined from temperature-dependent magnetization and hysteresis loop measurements. These results indicate the formation of novel ferromagnetic multilayers, which may have spintronic applications.
TL;DR: In this paper, the switching dynamics of a double-barrier Josephson junction is analyzed as a function of the microscopic properties of its electrodes, and it is found that the nonstationary behavior of the Josephson phase difference is very sensitive to dissipation mechanisms acting inside the intrinsic shunt.
Abstract: The switching dynamics of a double-barrier Josephson junction is analyzed as a function of the microscopic properties of its electrodes. In particular, it is found that the nonstationary behavior of the Josephson phase difference is very sensitive to dissipation mechanisms acting inside the intrinsic shunt. The leading factor that determines the dissipation is the local electron density of states N(E) inside the electrodes. The roles of junction geometry, electrode purity, and interface quality are discussed and how they affect the details of N(E), hence the resulting phase dynamics. The microscopic analyses allow optimization of the performance of double-barrier Josephson junction-based rapid-single-flux-quantum circuits in two ways: 1) decreasing the switching time of Josephson elements and 2) reducing the excess wiring. Such an analysis is facilitated with the aid of a lumped circuit representation which generalizes the nonlinear resistive-shunted-junction model.
TL;DR: In this paper, the authors studied the luminescence of 1s orthoexcitons in Cu 2 O under both resonant and non-resonant two-photon excitation.
18 Oct 2004
TL;DR: In this paper, interference patterns formed by the intersection of two coherent laser beams result in periodic one-dimensional potential wells ("optical trenches"), and polystyrene spheres become trapped in these potential wells and subsequently self-assemble into a two-dimensional periodic structure.
Abstract: We present preliminary results from an experimental study of optically-assisted assembly. Interference patterns, formed by the intersection of two coherent laser beams, result in periodic one-dimensional potential wells ("optical trenches"). Polystyrene spheres become trapped in these potential wells and subsequently self-assemble into a two-dimensional periodic structure. The spacing between optical trenches is adjusted dynamically, which offers the freedom to dynamically control the lattice constant, offering a recipe for defect-free assembly which begins with annealing at large lattice constant and subsequent compression into a close-packed structure.
TL;DR: Magnetic MnGeAsP films with the nominal composition MnGe(As1−xPx)2 were grown on GaAs(100) by solid source molecular beam epitaxy.
Abstract: Magnetic MnGeAsP films with the nominal composition MnGe(As1−xPx)2 were grown on GaAs(100) by solid source molecular beam epitaxy. The films were grown keeping the Mn, Ge, and As fluxes constant while varying the P flux via its cell temperature. A streaky reflection high energy electron diffraction pattern with intensity variations along each reflection line was observed, suggesting small domain sizes in the films. The incorporation of P in the films was examined by x-ray photoelectron spectroscopy, and an increase of the P/As peak ratio was observed with increasing phosphorous cell temperature. Superconducting quantum interference device magnetic measurements revealed a clear change in the magnetic properties as phosphorous was introduced into the films. The coercive field decreases with increasing P/As ratio. The measured Curie temperatures were over 380 K for P/As ratios larger than 2, which is higher than that of a nominal MnGeAs2 and MnGeP2 film.
TL;DR: In this article, the anomalous Hall effects at room temperature with p-type conductivity and temperature-dependent hysteresis loops in the magnetization were investigated on MnAs∕GaAs digital alloys, where the reported Curie temperatures are at or below 50K.
Abstract: Ge∕MnAs multilayers are grown on (001) GaAs substrates by molecular-beam epitaxy. All samples investigated showed strong anomalous Hall effects at room temperature with p-type conductivity and temperature-dependent hysteresis loops in the magnetization. Ge∕MnAs multilayers also revealed an in-plane magnetic easy axis and a vanishingly small in-plane magnetic anisotropy. These results are in sharp contrast to MnAs∕GaAs digital alloys, where the reported Curie temperatures are at or below 50K, and demonstrate the potential of germanium-based spintronic devices.
TL;DR: In this article, the authors describe instrumentation and measurement procedures for performing microwave measurements on small metallic samples at dilution refrigerator temperatures using the microwave cavity perturbation technique using the lead-plated cavity.
Abstract: We describe instrumentation and measurement procedures for performing microwave measurements on small metallic samples at dilution refrigerator temperatures using the microwave cavity perturbation technique. The quality factor Q of the lead-plated cavity was of order of 105 at temperatures below the superconducting transition temperature of lead. Microwaves were coupled into and out of the resonator through two room-temperature positionable semirigid coaxial lines, each terminated in a small-loop antenna. We describe in detail the arrangement of the apparatus used to tune to, and lock onto, a cavity resonance and the strategy used to categorize various resonance modes. One of the main features of this microwave spectrometer is the application of the FM detection method to measure changes in both the frequency and the quality factor of the sample-loaded cavity. The procedures for converting these quantities to the real and imaginary components of the surface impedance are described. As an application of th...