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We have recently carried out exploratory dynamic experiments where the samples were subjected to prescribed thermodynamic paths. In typical dynamic compression experiments, the samples are thermodynamically limited to the principal Hugoniot or quasi-isentrope. With recent developments in a functionally graded material impactor, we can prescribe and shape the applied pressure profile with similarly shaped, nonmonotonic impedance profile in the impactor. Previously inaccessible thermodynamic states beyond the quasi-isentropes and Hugoniot can now be reached in dynamic experiments with these impactors. In the light gas gun experiments on copper reported here, we recorded the particle velocities of the Cu–LiF interfaces and have employed hydrodynamic simulations to relate them to the thermodynamic phase diagram. Peak pressures for these experiments are on the order of megabars, and the time scales range from nanoseconds to several microseconds. The strain rates of these quasi-isentropic experiments are approximately 104–106s−1 in samples with thicknesses of up to 5mm. Though developed at a light gas gun facility, such shaped pressure profiles are also feasible using laser ablation or magnetically driven compression techniques and allow for previously unexplored directions to be taken in high pressure physics.

We have studied the magnetic characteristics of the critical states of Y-Ba-Cu-O and Eu-Ba-Cu-O high-${T}_{c}$ superconductors. Magnetization data at various temperatures have revealed a very large magnetic hysteresis. The highly irreversible behavior was found to exist both in bulk samples and in well-isolated particles. These effects are consistent with the existence of large pinning forces caused by the structural defects in these materials. By analyzing the hysteretic magnetization data, the critical current density ${J}_{c}$ as a function of the external magnetic field has been obtained at several temperatures. The variation of the trapped flux with temperature (up to ${T}_{c}$) has also been measured.

We used Zn and Ga, two unique dopants having definite valence states and filled 3d levels, to substitute preferentially on the Cu(2) and Cu(1) sites in the ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ superconductor. Small doping of Ga induces an orthorhombic-to-tetragonal structural transition, but the values of ${\mathrm{T}}_{\mathrm{c}}$ are as high as 81 K in the tetragonal phase. Our results indicate that the oxygen-vacancy order, or the linear-chain structure, is not essential. We also find that the Cu(2) sites are much more crucial than the Cu(1) sites in sustaining the high ${\mathrm{T}}_{\mathrm{c}}$.

Percolation behaviors of normal-state conductivity and superconductivity have been studied in a Au-Y${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ granular system. The normal-state conductivity shows a percolation threshold at a Au volume fraction ${p}_{\mathrm{Au}}$ of 23%, whereas the superconducting network shows a threshold at ${p}_{\mathrm{Au}}\ensuremath{\sim}60%$. The presence of Au has negligible effect on the superconducting Y${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ phase. In the dilute limit, the ratio of the Meissner signal to the diamagnetic-shielding signal approaches unity.

Magnetic properties of superconducting RBa 2 Cu 3 O 6+y compounds ( R = Nd , Sm, Eu, Gd, Dy, Ho, Er, Tm and Yb) have been studied by using a SQUID magnetometer in the temperature range of 3 – 400 K. The susceptibility data of most of the samples can be well described by the Curie-Weiss relation. The rare earth ions exhibit essentially the full magnetic moments expected for the R 3+ states, while the superconducting transition temperature remains in the 88 – 94 K range. The rare earth moments are generally found to interact antiferromagnetically. However, no magnetic order is observed in the temperature range studied. The Eu samples exhibited anomalous susceptibilities which we ascribe to the low-lying states of the 7 F J manifold of Eu 3+ .

Superconducting Au‐YBa2Cu3O7 composites have been fabricated over a Au volume fraction range of 0–100%. Microstructure measurement indicates that Au and YBa2Cu3O7 form well‐separated phases. The superconducting transition temperature Tc was found unaffected by the presence of Au. The composites exhibit low normal state resistivity and much improved ductility. The results suggest that Au is an excellent metal host for making ultrafine YBa2Cu3O7 granular solids.

One of the outstanding questions concerning the high-temperature superconductor YBa2Cu3O7 is the relative importance of the CuO2 planes (Cu(2) site) and the CuO chains (Cu(1) site). Many theories1,2 have stressed the importance of the 3d holes at the Cu sites, which provide an antiferromagnetic correlated background necessary for the coupling of the superconducting electrons. We have substituted Zn(3d104s2) and Ga(3d104s24p1) in the Cu(2) and Cu(1) sites, respectively, while maintaining the oxygen stoichiometry at 7. In the valence states of 2 + and 3 + respectively, the 3d bands of both elements are completely full, without the complication of a magnetic moment. Here we discuss the structural changes that accompany Zn and Ga substitution, as deduced from X-ray and neutron diffraction, and correlate these changes with the superconducting properties. We show that the integrity of the planes is much more important than that of the chains in sustaining high-Tc superconductivity.

Superconducting YBa2Cu3O7 thin films have been prepared by using a magnetron sputtering system in the single‐source mode. Samples deposited on [100] single‐crystal MgO with and without a Au buffer layer all show high transition temperatures (82–87 K). The use of a Au buffer layer significantly improves the superconducting properties, particularly the Meissner effect and critical current density (3.3×106 A/cm2 at T=2 K and 3.5×104 A/cm2 at T=77 K). The Au films remain metallic after high‐temperature annealing in an oxygen atmosphere. We propose to use Au buffer layers as current shunts to protect superconducting films and devices.

We present the results of a comparison between the magnetic properties of granular Fe–Al2O3 and Fe–SiO2. Granular Fe-SiO2 was found earlier to display an anomalous increase in coercivity which appears to scale with the Fe grain size. The Fe-Al2O3 samples were prepared under similar conditions and their magnetic properties determined. The coercivity in granular Fe-Al2O3 is also seen to increase with increasing grain size, showing that the effect is not unique to the Fe-SiO2 system. A major difference between granular Fe–Al2O3 and Fe–SiO2 is the size of the Fe grains, which are smaller in Al2O3.

A thermodynamic model is presented which predicts a significant sample size effect on the elastic moduli of superlattice thin films possessing small bilayer repeat lengths. Owing to the presence of incoherent (incommensurate) interfacial stresses, biaxial in-plane strains are created which are approximately inversely proportional to the bilayer repeat length Λ. When Λ is of the order of 1 nm, these strains can be of the order of 1%, inducing nonlinear elastic behavior. This model is able to explain in a quantitative way the existence of a “supermodulus” effect in certain metallic superlattices.

We have used Zn and Ga, two unique dopants having definite valence states and filled 3d levels, to probe the YBa2Cu3O7 superconductor. A small doping of Ga induces an orthorhombic to tetragonal structural transition, but the values of Tc are as high as 81 K in the tetragonal phase. YBa2(Cu1−xZnx)3O7 retains the same orthorhombic structure as the parent compound, but with highly depressed Tc. The oxygen vacancy order, or the linear chain structure, is found to be not essential for the high Tc. Our data suggest that Ga and Zn preferentially substitute Cu(1) and Cu(2) sites, which leads to the conclusion that the most important feature of the high Tc oxide superconductors is the Cu—O2 planes.

We have fabricated samples of the form ${\mathrm{YBa}}_{2}$(${\mathrm{Cu}}_{0.9}$${\mathrm{A}}_{0.1}$${)}_{3}$${\mathrm{O}}_{6+\mathrm{y}}$ where A=Ti, Cr, Mn, Fe, Co, Ni, Cu, and Zn. The superconducting state was investigated by both resistance and magnetization measurements. In addition, the magnetic susceptibility above ${T}_{c}$ has been measured. ${T}_{c}$ was found to be strongly correlated with the size of the paramagnetic moments, largely due to scattering from the magnetic sites. In the sample containing Zn, however, ${T}_{c}$ was dramatically reduced due to filling of the antibonding d band.

Superconducting YBa2Cu3O; thin films have been prepared by magnetron sputtering onto [100] single crystal MgO with and without an Au buffer layer. All samples show high transition temperatures (82–87 K). The use of an Au buffer layer significantly improves the superconducting properties, particularly the Meissner effect and critical current density (3.3×106A/cm2 at 2 K and 3.5×104A/cm2 at T=77 K). The Au buffer layers remain metallic after high temperature annealing in an oxygen atmosphere, and may thus serve as effective current shunts.

The ibm® Blue Gene®/q (bg/q) supercomputer system was developed in partnership between ibm, the Argonne National Laboratory, and the Lawrence Livermore National Laboratory. Blue Gene/Q is a bright example of the United States Department of Energy and IBM's capability and seamlessly brings together science and technology and the people that make this possible. Mira is a system, due in large part to the insights gained through years of partnership on the Blue Gene family among Argonne, Lawrence Livermore, and ibm. The ibm®Blue Gene®/l supercomputer debuted in November 2004, followed by the second generation three years later. Indeed, the second and third generations, called Blue Gene®/p and Blue Gene®/q, respectively, were conceived before Blue Gene/L was formally announced. With the deployment of Sequoia in Livermore, and the Mira 48-rack system in Argonne, Blue Gene/Q began to accumulate its trophies. The system software objectives on Blue Gene/Q are ultra-scalability, high reliability, and delivering the full performance capability of the hardware to applications.