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Physics

Condensed matter

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Displaying 1026 - 1050 of 1242

Anomalous thermal behavior in microcalorimeter gamma-ray detectors

July 20, 2009
Author(s)
Robert D. Horansky, James A. Beall, Kent D. Irwin, Joel N. Ullom
Improving the resolution of gamma-ray detectors is important for many fields, including determinations of the Lamb shift in atoms with high atomic numbers , nuclear treaty verification , and environmental monitoring. High-purity germanium detectors are

The-Final-State Symmetry of Na 1s Core-shell Excitons in NaCl and NaF

July 8, 2009
Author(s)
Eric L. Shirley, K. P. Nagle, G T. Seidler, T. T. Fister, J. A. Bradley, F. C. Brown
We report measurements of the Na 1s contribution to the nonresonant inelastic x-ray scattering (NRIXS) from NaCl and NaF. Prior x-ray absorption studies have observed two pre-edge excitons in both materials. The momentum transfer-dependence (q-dependence)

Inter-Laboratory Comparisons of NbTi Critical Current Measurements

June 22, 2009
Author(s)
Arno Godeke, D. Turrioni, T. Boutboul, Najib Cheggour, A. K. Ghosh, Loren F. Goodrich, M Meinesz, A. den Ouden
We report on a multi-institute comparison of critical current data, measured on a modern Large Hadron Collider (LHC) NbTi wire that has shown a standard deviation below 1% in critical current density spread in more than 1500 measurements. Inter-laboratory

Internal tin Nb3Sn conductors engineered for fusion and particle accelerator applications

June 22, 2009
Author(s)
Jeffrey Parrell, Y. Zhang, Michael Field, M Meinesz, Yonghua Huang, H Miao, Seungok Hong, Najib Cheggour, Loren F. Goodrich
The critical current density (Jc) of Nb3Sn strand has been significantly improved over the last several years. For most magnet applications, high Jc internal tin has displaced bronze process strand. The highest Jc values are obtained from distributed

Number Fluctuations and Energy Dissipation in Sodium Spinor Condensates

June 5, 2009
Author(s)
Yingmei Liu, Eduardo N. Gomez, Stephen E. Maxwell, Lincoln D. Turner, Eite Tiesinga, Paul D. Lett
We characterize fluctuations in atom number and spin populations in F = 1 sodium spinor condensates. The time evolution of the population fluctuations shows a maximum. We interpret this as evidence of a dissipation-driven separatrix crossing in phase space

Topological Insulators and Metals in Atomic Optical Lattices

May 28, 2009
Author(s)
Tudor Stanescu, Victor Galitski, Jay Vaishnav, Charles W. Clark, Sankar Das Sarma
We propose the realization of topological quantum states with cold atoms trapped in an optical lattice. We discuss an experimental setup that generates a two-dimensional hexagonal lattice in the presence of a light-induced periodic vector potential, which

Observing the Quantization of Zero Mass Carriers in Graphene

May 15, 2009
Author(s)
Joseph A. Stroscio, Gregory M. Rutter, D. L. Miller, K. Kubista, W. A. de Heer, Phillip N. First
Application of a magnetic field to conductors causes the charge carriers to circulate in cyclotron orbits with quantized energies called Landau levels (LLs). These are equally spaced in normal metals and two-dimensional electron gases. In graphene, however

Time domain measurement of phase noise in a spin torque oscillator

May 13, 2009
Author(s)
Mark W. Keller, Anthony B. Kos, Thomas J. Silva, William H. Rippard, Matthew R. Pufall
We measure phase noise from the zero crossings of the voltage vs. time waveform of a spin torque nanocontact oscillating in a vortex mode. The power spectrum of the phase noise varies with Fourier frequency f as 1/f 2, consistent with frequency

Phonon softening and anomalous mode near the x c = 0.5 quantum critical point inCa 2-x Sr x RuO 4

May 4, 2009
Author(s)
R. G. Moore, M. D. Lumsden, M. B. Stone, Jiandi Zhang, Ying Chen, Jeffrey Lynn, R. Jin, D Mandrus, E. W. Plummer
Inelastic neutron scattering is used to measure the temperature-dependent phonon dispersion in Ca2−xSrxRuO4(x=0.4,0.6). The in-plane Σ4 octahedral tilt mode softens significantly at the zone boundary of the high-temperature tetragonal (HTT) I41/acd

Itinerant spin excitations near the hidden order transition in URu2Si2

April 22, 2009
Author(s)
J. A. Janik, H. D. Zhou, Y.-J. Jo, L. Balicas, G. J. MacDougall, G. M. Luke, J. D. Garrett, K. J. McClellan, E. D. Bauer, J. L. Sarrao, Yiming Qiu, John R. Copley, Z. Yamani, W. J. Buyers, C. R. Wiebe
By means of neutron scattering we show that the high-temperature precursor to the hidden order state of the heavy fermion superconductor URu 2Si 2 exhibits heavily damped incommensurate paramagnons whose strong energy dispersion is very similar to that of

Cryocoolers: State of the art and recent developments

March 31, 2009
Author(s)
Ray Radebaugh
Cryocooler performance and reliability are continually improving. Consequently, they are more and more frequently implemented by physicists in their laboratory experiments or for commercial and space applications. The five types of cryocoolers most

Structure and Degeneracy of Vortex Lattice Domains in Pure Superconducting Niobium: A Small-Angle Neutron Scattering Study

January 27, 2009
Author(s)
Mark Laver, E M. Forgan, C Bowell, C D. Dewhurst, S Ramos, A B. Abrahamsen, D. K. Christen, D Fort, S Muhlbauer, J Kohlbrecher, R Cubitt
High-purity niobium exhibits a surprisingly rich assortment of vortex lattice (VL) structures for fields applied parallel to a fourfold symmetry axis, with all observed VL phases made up of degenerate domains that spontaneously break some crystal symmetry

3:1 Magnetization Plateau and Suppression of Ferroelectric Polarization in an Ising Chain Multiferroic

January 26, 2009
Author(s)
Y.-J. Jo, Seoungsu Lee, E. Choi, H. Yi, William D. Ratcliff, Y. Choi, V. Kiryukhin, S.-W. Cheong, L. Balicas
Ferroelectric Ising chain magnet Ca3Co2−xMnxO6 (x≃0.96) was studied in magnetic fields of up to 33 T. Magnetization and neutron-scattering measurements reveal successive metamagnetic transitions from the zero-field ↑↑↓↓ spin configuration to the ↑↑↑↓ state

Origin and Tuning of the Magnetocaloric Effect in the Magnetic Refrigerant Mn1.1Fe0.9(P0.8Ge0.2)

January 26, 2009
Author(s)
Danmin Liu, Ming Yue, Jiuxing Zhang, T. M. McQueen, Jeffrey Lynn, Xiaolu Wang, Ying Chen, Jiying Li, R. J. Cava, X. Liu, Zaven Altounian, Qingzhen Huang
Neutron-diffraction and magnetization measurements have been carried out on a series of samples of the magnetorefrigerant Mn1+yFe1−yP1−xGex. The data reveal that the ferromagnetic and paramagnetic phases correspond to two very distinct crystal structures

Striped Domains at the Pentacene:C 60 Interface

January 12, 2009
Author(s)
Dan B. Dougherty, W Jin, J Cullen, J Reutt-Robey, Steven W. Robey
STM observations of the initial growth stages of the first layer of pentacene on a monolayer film of C60 on Ag(111) are presented. Pentacene films nucleate and grow with molecules standing up at the Pentacene:C60 interface similar to the well known thin

Spin Correlations in the Geometrically Frustrated Pyrochlore Tb 2 Mo 2 O 7

December 31, 2008
Author(s)
D. K. Singh, J. S. Helton, S. Chu, T. Han, C. Bonnoit, Sung Chang, Hye J. Kang, Jeffrey W. Lynn, Y. S. Lee
We report neutron scattering studies of the spin correlations of the geometrically frustrated py- rochlore Tb 2Mo 2O 7using single crystal samples. Elastic diffuse peaks are observed at low temperatures, indicating short-range ordering of the Tb 3+ moments

Neutron-Diffraction Measurements of Magnetic Order and a Structural Transition in the Parent BaFe2As2 Compound of FeAs-Based High-Temperature Superconductors

December 17, 2008
Author(s)
Qingzhen Huang, Yiming Qiu, Wei Bao, Mark Green, Jeffrey Lynn, Y. C. Gasparovic, T. Wu, G. Wu, X. H. Chen
The recent discovery of superconductivity in (Ba,K)Fe2As2, which crystallizes in the ThCr2Si2 (122) structure as compared with the LnFeAsO (Ln is lanthanide) systems that possess the ZrCuSiAs (1111) structure, demonstrates the exciting potential of the

Pressure-induced volume-collapsed tetragonal phase of CaFe 2 As 2 as seen via neutron scattering

November 24, 2008
Author(s)
A. Kreyssig, Mark Green, Y. Lee, G. D. Samolyuk, Pawel Zajdel, Jeffrey Lynn, S. L. Bud'ko, M. S. Torikachvili, N. Ni, S. Nandi, Juscelino Leao, Sarah Poulton, D. N. Argyriou, B. N. Harmon, R. J. McQueeny, P. C. Canfield, A. I. Goldman
Recent investigations of the superconducting iron-arsenide families have highlighted the role of pressure, be it chemical or mechanical, in fostering superconductivity. Here we report that CaFe2As2 undergoes a pressure-induced transition to a nonmagnetic

Josephson phase qubit circuit for the evaluation of advanced tunnel barrier materials

November 21, 2008
Author(s)
Jeffrey S. Kline, Haohua Wang, Seongshik Oh, John M. Martinis, David P. Pappas
We have found that crystalline Josephson junctions have critical current density control problems which decrease circuit yield. We present a qubit circuit designed to accommodate a factor-of-five variation in critical current density for the evaluation of

Unusual Heavy-mass Nearly Ferromagnetic State with a Surprisingly Large Wilson Ratio in Double Layered Ruthenates (Sr 1-x Ca x ) 3 Ru 2 O 7

November 14, 2008
Author(s)
Z Qu, L Spinu, H Q. Yuan, V Dobrosavljevic, Wei Bao, Jeffrey Lynn, M Nicklas, J Peng, T J. Liu, F Fobes, E Flesch, Z Q. Mao
We report a very unusual heavy-mass nearly ferromagnetic state with a surprisingly large Wilson ratio Rw (e.g., Rw 700 for x = 0.2) in double layered ruthenates (Sr 1- xCa x) 3Ru 2O 7. This state does not evolve into a long-range ferromagnetic order
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