We have directly observed 0.75±0.2 Gbar planar shocks in gold target foils impacted by ablatively driven gold flyer foils. The x-ray drive for the flyer foils was produced in a gold Hohlraum by ten beams of the Nova laser. The dynamic pressure inferred by shock velocity measurements is more than a factor of 7 greater than previous dynamic shocks produced in the laboratory and over a surface area significantly larger than most previous ultrahigh pressure experiments. The technique allows the laboratory investigation of equations of state in the gigabar regime.

Measurements of the undercooling temperature of crystallization of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$, ${}_{}{}^4{}_{}{}^{}\mathrm{He}$, and Ne fluids show that there exists a temperature ${\mathit{T}}_{\mathit{a}}$ along the melting curve of each system below which no undercooling is observed and above which the undercooling temperature is a linear function of the melting temperature at the same pressure. When the melting temperature is normalized by ${\mathit{T}}_{\mathit{a}}$, the measurements in the three systems scale perfectly. ${\mathit{T}}_{\mathit{a}}$ is seen to be a linear function of 1/m, m being the mass number, and the observed undercooling can be explained through standard nucleation theory.

Light scattering has been used to study a mixture of 3-methylpentane and nitroethane undergoing spinodal decompositon. The scattered intensity has been measured in absolute units allowing the first test of theory with no adjustable parameters. The measured structure factor does not evolve according to theory even when the initial fluctuations are taken into account. We believe the reason is that the evolving concentration field causes the sample temperature to change continuously throughout the decomposition process.

The critical velocity for the onset of phase slips in the flow of superfluid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ through a micro-orifice has been found to be strongly affected at temperatures below ∼0.1 K by minute quantities of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ impurities, in the few parts per billion range. It is shown that this effect yields essential information on the vortex nucleation mechanism and in particular the local superfluid velocity at which vortices are formed, which is 22 m/s in these experiments.

The diffusion of sodium adatoms on a Cu(001) surface has been studied with quasielastic helium atom scattering. A jump mechanism was found with activation energy 51 meV, jump length 2.56 Å, and jump attempt frequency ${\nu }_0$ 0.53 THz. The adatom vibrational frequency parallel to the surface is measured to be 1.23 THz. The data are interpreted with the aid of a realistic molecular-dynamics simulation which reveals that ${\nu }_0$ is governed by the rate of energy exchange between the adatoms and the substrate, and not, as transition state theory would predict, by the vibrational frequencies of the adatom.

High temperature scanning tunneling microscopy (STM) measurments are performed to study the behavior of monatomic step edges on Si(001) at elevated temperatures. The freeze out temperature ${\mathit{T}}_{\mathit{f}}$, at which the roughness of these step edges is frozen out, is estimated to be well above the intrinsic roughening temperature ${\mathit{T}}_{\mathit{r}}$ of the edges. This means that these step edges are always rough at room temperature. The 1D random walk behavior of the step edges, as determined from room temperature STM images, suggests that the step-step interaction is very weak compared to the kink formation energies.

Introducing holes (or partly eliminating electrons) in Mott-Hubbard insulator ${\mathrm{LaTiO}}_3$ (with 3${\mathit{d}}^1$ configuration) can be carried out by partial substitution of La with Sr, which produces the strongly correlated metallic phase. Systematic variation of electronic properties in ${\mathrm{Sr}}_{1\mathrm{-}\mathit{x}}$${\mathrm{La}}_{\mathit{x}}$${\mathrm{TiO}}_3$ was investigated as a function of the 3d band filling (x) by measurements of resistivity, Hall coefficient, magnetic susceptibility, and specific heat. Up to the vicinity of the metal-insulator phase boundary (${\mathit{x}}_{\mathit{c}}$∼0.95), ${\mathrm{Sr}}_{1\mathrm{-}\mathit{x}}$${\mathrm{La}}_{\mathit{x}}$${\mathrm{TiO}}_3$ behaves as a Fermi liquid system where the carrier mass and scattering rate critically increase as the x=1 (${\mathrm{LaTiO}}_3$) insulator is approached.

Spatially separated electron-hole layers in strong magnetic fields are studied by exactly diagonalizing the Hamiltonian of a small number of particles. When the separation between layers is of the same order as the intralayer particle separation, the ground-state energy of the system displays a pronounced cusp as a function of the Landau level degeneracy at an odd denominator fraction ν${\mathrm{̃}}_{\mathit{c}}$, where ν${\mathrm{̃}}_{\mathit{c}}$==(${\nu }_{\mathit{e}}$-${\nu }_{\mathit{h}}$)/(1-${\nu }_{\mathit{h}}$), and ${\nu }_{\mathit{e}}$ and ${\nu }_{\mathit{h}}$ are the electron and hole filling factors (${\nu }_{\mathit{h}}$≪${\nu }_{\mathit{e}}$). Detailed analysis suggests that the ground state responsible for the cusp consists of stable ions (composed of Laughlin quasiparticles bound to a hole) weakly coupled to an incompressible fluid state of the remaining electrons.

Starting from the usual formulation of nonequilibrium quantum statistical mechanics, the expectation value of an operator A in a steady state nonequilibrium quantum system is shown to have the form 〈A〉 =Tr{${\mathit{e}}^{\mathrm{-}\mathrm{\beta }\left(\mathit{H}\mathrm{-}\mathit{Y}\right)}$A} /Tr{${\mathit{e}}^{\mathrm{-}\mathrm{\beta }\left(\mathit{H}\mathrm{-}\mathit{Y}\right)}$}, where H is the Hamiltonian, β is the inverse of the temperature, and Y is an operator which depends on how the system is driven out of equilibrium. Because 〈A〉 is not expressed as a sum of correlation functions integrated over real time, one can now consider performing nonperturbative calculations in interacting nonequilibrium quantum problems.

Using an exact single-particle scattering formalism we have carried out the first calculation of the conductance of a metallic contact, on the basis of a full dynamic simulation of the evolution of its atomic structure. We find that the contact area evolves discontinuously through a series of mechanical instabilities, which is reflected in a stepwise variation of the conductance also seen in recent experiments. Importantly, we find that the conductance is not simply proportional to the size of the contact and, therefore, the conductance per atom is not constant.

The spin injection technique has been used to study the transport of spin polarized conduction electrons in gold films, and has resulted in the unique observation of a large ‘‘spin bottleneck’’ effect. Furthermore, the measured spin diffusion length is surprisingly long.

Coulomb coupling between spatially separated quasi-two-dimensional electron and hole gases is studied as a function of temperature and/or electron (hole) gas density. Because of the exclusion principle mainly electrons and holes of antiparallel spin screen the electron-hole interaction at low densities. The coupling is described by a generalized random-phase approximation which takes into account exchange processes to all orders of the Hartree-Fock potential. The temperature dependence of the transimpedance agrees very well with experiment for relatively high densities; its density dependence agrees well for high densities and reasonably well for low and intermediate densities.

Cyclotron resonance on low density, 2D electron systems in the ultra-quantum limit show split and shifted resonances. This demonstrates the presence in the ground state of both spin orientation electrons, whose relative proportion is strongly temperature and occupancy dependent. A critical occupancy of ∼1/10 divides single-particle behavior in a gaseous phase from the quantum liquid where the resonance positions are temperature and carrier density dependent. The resonances suggest a mixed spin state for some regions of the liquid phase.

We have measured tunneling rates out of an electron layer trapped at a liquid-helium–vacuum interface in the presence of a magnetic field. When the field is transverse to the escape direction we find a striking suppression of the tunneling rates: a field of 3000 G at 40 mK reduces the tunneling current by four orders of magnitude. As the temperature increases the magnetic suppression of tunneling diminishes until it disappears completely above 250 mK. By contrast parallel fields have no effect on the tunneling rates.

We show that the existence of the Magnus force is a general property of a vortex line in a superconductor by calculating the Berry phase for an adiabatic motion around a closed loop at zero temperature. We find that there is no influence of the disorder and the electromagnetic field on the existence of the Magnus force in the superconducting state, and its magnitude is proportional to the superfluid electron density.

Detailed measurements and analysis of the temperature and magnetic field dependence of the magnetization and the magnetic relaxation of Nb films have been carried out. An irreversibility line has been identified, below which the remanent magnetization was found to decay logarithmically in time. The data were quantitatively compared to predictions of flux creep, vortex glass, and vortex-lattice-melting models. Only the vortex-lattice-melting model self-consistently explained the data.

Unusually large magnetostriction for a superconductor was found in a single crystal of the high-${\mathit{T}}_{\mathit{c}}$ cuprate ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_8$. The sample length change was measured along the ab plane under magnetic fields applied up to 6 T parallel to the c axis. The sample decreased in length during the field increasing process and with relative change exceeding ${10}^{\mathrm{-}4}$ at 4.8 K. A quantitative model has been proposed which accounts for the magnetostriction in terms of internal forces arising from flux pinning. These observations show that magnetostriction measurement is a novel and unique technique to investigate the pinning effect and related phenomena in type-II superconductors.

While the growth rate of the average volume in a three-dimensional polycrystal is well understood, the growth rates of individual grains (which determine material properties through the topological and volume distributions) are not known. Using a three-dimensional Q-state Potts model simulation, I find that the average canonical growth rate of a grain depends linearly on its number of faces and is independent of its volume, a surprisingly simple and unexplained result.

We show that discrete detonation chemistry can be studied using molecular dynamics simulations. A model 2D semi-infinite energetic molecular solid described by reactive many-body potentials is shown to support a chemically sustained shock wave with properties that are consistent with experimental results and the classic continuum theory of planar detonations. These promising results demonstrate for the first time that simulations using reactive many-body potentials provide a powerful probe of the interplay between the continuum properties of shock waves and the atomic-scale chemistry they induce in condensed-phase detonations.

We present a new microscopic theory for the frequency (ω) and density (φ) dependent complex shear viscosity η(φ,ω) of dense hard sphere colloids near equilibrium. The predictions are in good agreement with experimental results for silica spheres dissolved in cyclohexane.