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Physics

Condensed matter

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Displaying 1001 - 1025 of 1275

Bethe-Salpeter Equation Calculations of Core Excitation Spectra

March 4, 2011
Author(s)
Eric L. Shirley, Vinson T. John, John J. Rehr, Joshua J. Kas
We present a hybrid approach for GW/Bethe-Salpeter Equation (BSE) calculations of core excitation spectra, including x-ray absorption (XAS), electron energy loss spectra (EELS), and nonresonant inelastic x-ray scattering (NRIXS). The method is based on ab

Two Level System Loss in Superconducting Microwave Resonators

January 13, 2011
Author(s)
David P. Pappas, Michael R. Vissers, David S. Wisbey, Jeffrey S. Kline, Jiansong Gao
High quality factor, i.e. low loss, resonators are important for quantum information storage and addressing. In this work we study the resonance frequency and loss in superconducting coplanar waveguide resonators as a function of temperature and power. We

Evidence that the reversible strain effect on critical current density and flux pinning in Bi2Sr2Ca2Cu3Ox tapes is caused entirely by the pressure dependence of the critical temperature

December 23, 2010
Author(s)
Daniel C. van der Laan, J. F. Douglas, Cameron C. Clickner, Theodore C. Stauffer, Loren F. Goodrich, Hans J. van Eck
It is well known that the critical temperature of cuprate- and iron-based high-temperature superconductors changes with pressure. YBa 2Cu 3O 7-δ coated conductors, as well as Bi 2Sr 2CaCu 2O x and Bi 2Sr 2Ca 2Cu 3O x tapes and wires, show a clear

Engineering Time-Reversal Invariant Topological Insulators With Ultra-Cold Atoms

December 16, 2010
Author(s)
Ian B. Spielman, Nathan Goldman, Indubala I. Satija, Predrag Nikolic, Alejandro Bermudez, Miguel A. Martin-Delgado, Maciej Lewenstein
Topological insulators are a broad class of unconventional states that respect all symmetries of the system, but have non-trivial transport and topological properties which cannot be defined locally. Until recently, all known realizations of these phases

Modeling of Self-Heating Mechanism in the Design of Superconducting Limiters

December 10, 2010
Author(s)
Eduard Rocas, Juan C. Collado Gomez, Jordi Mateu, Nathan D. Orloff, James C. Booth
This work proposes a modeling method to simulate how temperature rise, due to power dissipation, affects the performance of a HTS limiter. The spatial temperature rise distribution across and along a HTS transmission line is determined by heat generation

Low loss superconducting titanium nitride coplanar waveguide resonators

December 9, 2010
Author(s)
Michael Vissers, Jiansong Gao, David S. Wisbey, David P. Pappas, C. C. Tsuei, A. D. Corcoles, Matthias Steffen
Thin films of TiN were sputter-deposited onto Si and sapphire wafers with and without SiN buffer layers. The films were fabricated into RF coplanar waveguide resonators, and internal quality factor measurements were taken at millikelvin temperatures in

Neutron Imaging Studies of Metal-Hydride Storage Beds

December 1, 2010
Author(s)
David Jacobson, Daniel Hussey, Elias Baltic, Terrence J. Udovic, John J. Rush, Robert C. Bowman
Neutron radiography and tomography were used to study the transient and steady-state distributions, respectively, of hydrogen within a prototypical, LaNi4.78Sn0.22-based hydrogen storage bed during and after various absorption and desorption steps. It was

Time-division SQUID multiplexers with reduced sensitivity to external magnetic fields

November 29, 2010
Author(s)
Greg Stiehl, Hsiao-Mei Cho, Gene C. Hilton, Kent D. Irwin, John A. Mates, Carl D. Reintsema, Barry L. Zink
We have developed time-division SQUID multiplexers to read out large arrays of transition-edge sensor (TES) detectors. These multiplexers are used in many applications that require exquisite control of systematic error. One important application is the

Electron Dynamics of Crystalline 4-He at High Pressures

October 29, 2010
Author(s)
Eric L. Shirley, H. K. Mao, Yang Ding, Peter Eng, Yong Q. Cai, Paul Chow, Yuming Xiao, Jinfu Shu, Russell J. Hemley, Chichang Kao, Wendy L. Mao
At high pressures, helium crystallizes as a unique insulator with the widest known electronic band gap. However, in the vicinity of the band gap and above, electronic excitations have been previously inaccessible to direct measurements. Using an optimized

Atomistic Factors Governing Adhesion between Diamond, Amorphous Carbon, and Model Diamond Nanocomposite Surfaces

October 1, 2010
Author(s)
Pamela L. Piotrowski, Rachel J. Cannara, Guangtu Gao, Joseph J. Urban, Robert W. Carpick, Judith A. Harrison
Complementary atomic force microscopy (AFM) and molecular dynamics (MD) simulations were conducted to determine the work of adhesion for diamond(111)(1x1) and diamond(001)(2x1) surfaces paired with other carbon-based materials. In the AFM experiments, the

The Cooper Pair Transistor

September 17, 2010
Author(s)
Jose A. Aumentado
The Cooper pair transistor (CPT) is a superconducting electrometer that has applications in quantum information as well as fundamental superconductivity studies. Since it operates in a near-dissipationless mode, it has potential as a minimally invasive

Phases of a 2D Bose Gas in an Optical Lattice

September 9, 2010
Author(s)
Karina K. Jimenez Garcia, Yu-Ju Lin, James V. Porto, Ian B. Spielman
Ultra-cold atoms in optical lattices realize essential models in condensed matter physics. Like with most experiments with ultra-cold atoms, our Rubidium-87 Bose Einstein condensate is confined in a harmonic trapping potential that persists even when

Theory for a Dissipative Droplet Soliton Excited by a Spin Torque Nanocontact

August 30, 2010
Author(s)
Mark Hoefer, Thomas J. Silva, Mark W. Keller
A distinct type of solitary wave is predicted to form in spin torque oscillators when the free layer has a sufficiently large perpendicular anisotropy. In this structure, which is a dissipative version of the conservative droplet soliton originally studied

Temperature dependence of the diffusive conductivity of bilayer graphene

August 24, 2010
Author(s)
Shaffique Adam, Mark D. Stiles
Assuming diffusive carrier transport and employing an effective medium theory, we calculate the temperature dependence of bilayer graphene conductivity due to Fermi-surface broadening as a function of carrier density. We find that the temperature

Band Structure of ABC-Stacked Graphene Trilayers

July 9, 2010
Author(s)
Fan Zhang, Bhagawan Sahu, Hongki Min, Allan H. MacDonald
The ABC-stacked N-layer-graphene family of two-dimensional electron systems is described at low energies by two remarkably flat bands with Bloch states that have strongly momentum-dependent phase differences between carbon \pi-orbital amplitudes on
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