The effect of shock wave profile shape on damage in copper G.T. Gray III, L.B. Addessio, E. Cerreta, C.A. Yablinsky (MST-8); D.D. Koller, R.S. Hixson, R.A. Rigg, J.D. Maestas (DE-9)
An understanding of damage evolution in a metal subjected to shock loading is critical to the development of predictive models of interest to Department of Energy and Department of Defense programs. Many investigations of dynamic damage or spall have been performed using flat-top shock waves. These experiments have shown that dwell time, strain rate, and peak stress can each influence the damage evolution. Metals that are subjected to direct high-explosive-driven shock loading, however, exhibit a triangular or Taylor wave loading/unloading
profile. Here the influence of shock wave profile shape on damage processes is investigated to understand the effects of peak stress and the development of tension in a specimen subjected to spallation loading.
Full article: LALP-06-092
Probing hidden magnetism and quantum criticality in unconventional superconductors T. Park, J.D. Thompson (MST-10)
An exotic form of superconductivity appears in classes of complex materials, such as the high-Tc cuprates and heavy-fermion compounds based on cerium, uranium and plutonium. Unlike conventional superconductivity in which electrons
form pairs by an attraction provided by lattice vibrations, unconventional superconductivity in these complex materials develops near some form of magnetic order. The proximity of magnetism and
unconventional superconductivity has led to speculation that fluctuations associated with magnetism may provide the glue that binds electrons into superconducting
pairs, and, moreover, if a magnetic transition could be tuned toward absolute zero temperature, fluctuations associated with this magnetic quantumcritical
point could be particularly effective in creating superconductivity. Several examples show that a maximum superconducting transition temperature Tc
occurs near a value of some tuning parameter, such as chemical composition or pressure, where a quantum-critical point would be expected, but
invariably, unconventional superconductivity intervenes to hide magnetism and prevent proof that a quantum-critical point exists. Using high pressures
and high magnetic fields, we explicitly identify a quantum-critical point in the heavy-fermion compound CeRhIn_5 (above). This discovery suggests a common
relationship among hidden magnetism, quantum criticality, and unconventional superconductivity in classes of strongly correlated electron materials. Full article: LALP-06-071
Above, at absolute zero temperature, unconventional superconductivity, formed by electron pairs dancing at the surface of an electron sea, hides a background of antiferromagnetism. Opening the veil
by applying a magnetic field reveals magnetism coexisting with superconducting electron partners. The boundary set by the curtain represents the quantum-phase transition.
Unconventional superconductivity in PuCoGa_5 N. Curro (MST-10) Superconductivity is a striking macroscopic phenomenon that is found in materials experiencing strong electron-electron interactions. The phenomenon was first observed by Kammerlingh Onnes in 1911, when he discovered that the electrical resistivity of elemental mercury suddenly vanished below a critical temperature, Tc. Below this temperature, the mercury was able to carry electrical current without dissipation. Over the years, many other elements and compounds were found to superconduct with different Tcs, typically on the order of 1-10K. Along with the discovery of these systems, several explanations emerged to explain the phenomenon on a microscopic level. But it was not until 1957 that John Bardeen and collaborators at the University of Illinois in Urbana were able to show theoretically that the superconductivity arose because the electrons experienced an attractive interaction brought about by the vibrations of the crystal lattice. Full article: LALP-06-072
Above, the nuclear magnetic resonance spectra of the gallium as the temperature evolves from below Tc (superconducting state) to
above Tc (normal state). The lower axis of the plane, parallel to the edge of the figure, is frequency, and the axis moving into the page is temperature. The
spectra shift to lower frequency in the superconducting state, reflecting the fact that the Cooper pairs form a spin singlet.
High temperature separation membranes for hydrogen purification and carbon capture K.A. Berchtold (MST-7), J.S. Young (X-2), K.W. Dudeck (MST-7)
While alternative and renewable energy sources will gradually increase their contributions to the
world's energy supply, most energy projections agree that conventional fossil energy
generation will continue to dominate for the foreseeable future. U.S. energy demand alone
currently results in billions of tons of annual carbon dioxide emissions. These greenhouse gas
emissions create a variety of environmental challenges and correspondingly, drive national and
international research and development initiatives focused on carbon sequestration. Full article: LALP-06-043
Above, this simplified model of the single tube membrane module
shows a mixed gas stream (composed of hydrogen, carbon dioxide ,
and other gases) entering the outer tube. The membrane
blocks most of the carbon dioxide but allows hydrogen to pass through
to the inner chamber where it can be collected and used as
fuel. The separated carbon-rich stream exits the outer tube at
high pressure, ready for transport to a carbon storage repository.
New approaches for study of substrate-supported phospholipid membranes A.P. Shreve (MST-CINT), A.M. Dattelbaum (MST-CINT), A.N. Parikh (UC, Davis)
Biology provides many examples of exquisite control of structure and dynamics in nanoscale assemblies.
Examples of functions of these assemblies include energy harvesting and transduction, ultrasensitive
chemical and biochemical recognition and sensing, and control of mineralization processes to produce
nanostructured inorganic and composite materials with unusual combinations of strength and
flexibility. All of these functions represent areas with important applications, and a major scientific challenge is
to improve our understanding of how to control complex self-assembly processes at the molecular and
supramolecular level in order to generate useful synthetic or biocomposite materials. Full article: LALP-06-038
Above, schematic geometry of neutron reflectivity experiment for lipid bilayers assembled
on nanoporous and nanocompsite silica thin films. Expanded view shows a transmission
electron microscope image of a nanoporous silica film.
Imaging spin-polarized electron transport in semiconductors S. A. Crooker (MST-NHMFL), D. L. Smith (T-11)
The ability to control and measure the spin of
an electron in semiconductors has been proposed
as the operating principle for a new
generation of spin-electronic, or "spintronic" devices.
By taking advantage of the electron's spin degrees of
freedom, today's charged-based microelectronics may
realize significant improvements in operating speed and
power consumption. Many designs for functional spintronic
devices have been recently proposed; for example,
the "spin transistor"-a device in which 'on' and
'off' states depend on whether the current-carrying electrons
are polarized spin-up or spin-down. Proposed
schemes for spintronic devices generally require three
essential elements: (i) a mechanism for electrically
injecting spin-polarized electrons into semiconductors,
(ii) a practical means for spin manipulation and transport,
and (iii) an electronic scheme for detecting the
resulting spin polarization. Full article: LALP-05-143
Above, a comparison of actual data [left], and the
results of a model [right] that is based on the spin drift diffusion
equations. Spin polarized electrons, optically
injected into GaAs [red dot], subsequently diffuse and
drift to the right under the influence of a small lateral
electric field [10V/cm]. Spin precession is caused by the
application of a uniaxial stress to the GaAs sample.
An exotic form of superconductivity appears in classes of complex materials, such as the high-Tc cuprates and heavy-fermion compounds based on cerium, uranium and plutonium. Unlike conventional superconductivity in which electrons
form pairs by an attraction provided by lattice vibrations, unconventional superconductivity in these complex materials develops near some form of magnetic order. The proximity of magnetism and
unconventional superconductivity has led to speculation that fluctuations associated with magnetism may provide the glue that binds electrons into superconducting
pairs, and, moreover, if a magnetic transition could be tuned toward absolute zero temperature, fluctuations associated with this magnetic quantumcritical
point could be particularly effective in creating superconductivity. Several examples show that a maximum superconducting transition temperature Tc
occurs near a value of some tuning parameter, such as chemical composition or pressure, where a quantum-critical point would be expected, but
invariably, unconventional superconductivity intervenes to hide magnetism and prevent proof that a quantum-critical point exists. Using high pressures
and high magnetic fields, we explicitly identify a quantum-critical point in the heavy-fermion compound CeRhIn_5 (above). This discovery suggests a common
relationship among hidden magnetism, quantum criticality, and unconventional superconductivity in classes of strongly correlated electron materials.
