Interactions of intense 400-fs laser pulses with a solid target are studied with time-integrated and time-resolved measurements. The latter are accomplished by means of a pump and probe experiment, in which the motion of the critical surface is measured with 250-fs resolution. It is found that when the average electron quiver energy (${\mathit{mv}}_{\mathrm{os}}^2$/2) becomes comparable to the electron thermal energy (${\mathit{kT}}_{\mathit{e}}$), the ponderomotive force of the high-intensity laser significantly reduces the thermal expansion of a laser plasma. This study is performed in an interesting regime not easily accessible with longer pulse lasers, in which the electron density scale length during the laser pulse was much less than the laser wavelength.

Using x-ray-absorption fine-structure measurements we have obtained clear evidence for structural anisotropy in amorphous sputter-deposited TbFe films exhibiting perpendicular magnetic anisotropy. Modeling of the data shows that perpendicular anisotropy in these films is associated with Fe-Fe and Tb-Tb pair correlations which are greater in plane and Tb-Fe correlations which are greater perpendicular to the film plane. Upon annealing at 300 °C the measured structural anisotropy disappears and the magnetic anisotropy decreases to a level consistent with magnetoelastic interactions between the film and substrate.

The angle-resolved electron intensity patterns of low energy Auger electrons and photoelectrons are calculated using a quantum mechanical electron scattering formalism with the inclusion of appropriate electron angular momentum. Calculations indicate that scattering of high angular momentum and low energy electrons exhibit miinima in the forward direction whereas low angular momenta or high energy electrons exhibit maxima, as is experimentally observed. Comparison of experimental and theoretical patterns allows for detailed structural characterizations.

Angular distributions of Auger electrons and of photoelectrons emitted at high (>500 eV) and low (<100 eV) kinetic energies are compared. The high-energy patterns can be interpreted as forward-projected images of real space crystal geometry. At low energies, the angular distributions are dominated by diffraction effects, and the structural information is no longer obvious. On the other hand, the sensitivity to the geometry and the atomic composition of the surface is here dramatically enhanced. Moreover, the angular momentum character of the source wave strongly influences these patterns.

Small-angle neutron scattering has been used to measure the influence of shear flow on a low-molecule-weight polymer blend near the critical point. When combined with light scattering measurements of the equilibrium (γ̇=0) critical dynamics, these measurements reveal that the long-range critical fluctuations begin to break apart when the shear rate becomes comparable to the characteristic relaxation rate ${\mathrm{\tau }}_{\mathit{c}}^{\mathrm{-}1}$, where ${\mathrm{\tau }}_{\mathit{c}}$ is the equilibrium lifetime of the critical fluctuations. This effect is directly related to the decrease in the critical temperature caused by the flow, and the data are found to be in very good agreement with the theoretical predictions of Onuki and Kawasaki.

A new method to determine eigenvectors based on a real space Green’s function is reported. This method is particularly useful for determining the eigenvectors corresponding to degenerate states. Using this approach, the lowest persistent degenerate mode exhibited by the third-stage Vicsek fractal has been examined and has been shown to be an edge-confined, superlocalized vibrational mode.

The vibrational properties of ${\mathrm{Si}}_{1/2}$${\mathrm{Ge}}_{1/2}$ alloys are studied using first principles interatomic force constants. The effects of disorder are either simulated using large supercells or treated at the mean-field level by the coherent-potential approximation. The latter approach fails not only to reproduce the details of the Raman spectra due to the local atomic environment, but even to predict the three-mode behavior of this alloy. Supercell calculations, on the contrary, are in good agreement with observed Raman spectra and shed light on the microscopic mechanisms responsible for their detailed features.

We report measurements of the effective viscosity and elasticity of a critical mixture of isobutyric acid and water in the process of phase separation under shear. The viscoelasticity of the sheared sample is a consequence of capillary forces associated with domain interfaces that produce linear domain growth in quiescent samples. We find agreement with a theory recently proposed by Doi and Ohta and obtain an estimate of the interfacial area per unit volume during spinodal decomposition.

Adsorbed n-hexadecane films of thickness ∼10, 20, and 40 Å are studied at 350 K via molecular-dynamics simulations. In the thickest film periodic oscillations of the density extend ∼18 Å from the solid-liquid interface, the roughness fluctuations at the liquid-vapor interface are Gaussian, and the density tail is fitted by an error function. Molecules in the first adsorbed layer lie preferentially parallel to the surface exhibiting domains of intermolecular orientational alignment. The diffusion is anisotropic with the component parallel to the surface greatly enhanced in the liquid-vapor region.

The minimum energy path is calculated for an ${\mathrm{H}}_2$ molecule dissociating on an Al(110) surface within local density functional theory. The properties of the potential energy surface along the five ${\mathrm{H}}_2$ ionic coordinates perpendicular to the reaction path are also determined and shown to be essential for an understanding of the dissociation dynamics.

An ellipsometric study of the cyclohexane-methanol mixture shows that in the wetting regime, either a very thin or a thick film is formed at the liquid/vapor interface. The observed hysteresis is consistent with the assumption that the wetting transition is first order. The thick layer can be accounted for by the stabilization of the wetting layer by long-range van der Waals forces. In agreement with this, the equilibrium wetting layer thickness shows no dependence on the temperature. The thin film is shown to be governed by short-range forces.

We use a mapping of the Kardar-Parisi-Zhang (KPZ) equation for interfacial growth to the equilibrium model of a directed polymer in a random medium to obtain the exact value of the dynamical exponent ${\mathit{z}}_{\mathit{c}}$ at the KPZ roughening transition. Our argument does not rely on perturbation theory and predicts that the value ${\mathit{z}}_{\mathit{c}}$=2 should be superuniversal, whenever thermal fluctuations are relevant at the corresponding equilibrium critical point in the directed polymer model.

We show than an ab initio molecular-dynamics scheme based on Vanderbilt ultrasoft pseudopotentials and a plane-wave expansion for the electronic orbitals allows one to perform accurate calculations for large systems containing tightly bound d-electron states. We use a novel real-space double-grid technique to deal efficiently with the localized augmentation functions in the core region. We apply our scheme in a full molecular-dynamics simulation of liquid copper at a temperature of 1500 K and find structural and dynamical properties that are in excellent agreement with experimental data.

We integrate numerically the time-dependent Schrödinger equation and show that a semi-infinite laser pulse can be used to localize an electron in one of the wells of a double-well quantum structure.

We discuss the electronic transmission through lateral dots, featuring both the Aharonov-Bohm-type oscillations observed in high magnetic field sweeps and Coulomb blockade oscillations detected as a function of electron density. We focus on the interplay of these two effects and demonstrate two intrinsic features of submicron dot behavior—the manifestation of the Aharonov-Bohn oscillations in a resonant reflection mode and a novel regime characterized by the simultaneous observation and a commensurate relationship of the two effects.

We have calculated the quasiparticle current through a superconducting island in the Coulomb blockade regime. The current depends strongly on the parity of the total number of free electrons in the island. This dependence reflects the difference between ground-state properties of the superconductor with even and with odd number of electrons.

We present experimental current-voltage (I-V) measurements on an Al-${\mathrm{Al}}_2$${\mathrm{O}}_3$-Al single-electron tunneling transistor in the superconducting state. We observe a variety of features which result from Cooper-pair tunneling processes. At low bias voltages and low temperatures we find that the I-V curve is 2e periodic with respect to the gate-induced charge. Remarkably, this periodicity persists up to 300 mK, a behavior which we interpret as strong evidence of an incremental free energy which depends on whether the number of electrons on the superconducting island is even or odd.

We study the normal state of the 2D attractive Hubbard model using quantum Monte Carlo simulations. We show that singlet pairing correlations develop above ${\mathit{T}}_{\mathit{c}}$, and the normal state of a short coherence length superconductor deviates from a canonical Fermi liquid. In the intermediate U regime, the spin susceptibility ${\mathrm{\chi }}_{\mathit{s}}$ is strongly temperature dependent, and the low-frequency spectral weight, as measured by the NMR relaxation rate 1/${\mathit{T}}_1$T, is shown to track ${\mathrm{\chi }}_{\mathit{s}}$. This provides a simple, qualitative explanation for the spin-gap behavior observed in several high-${\mathit{T}}_{\mathit{c}}$ systems.

Positive muons injected into solid ${\mathrm{C}}_{60}$, ${\mathrm{K}}_4$${\mathrm{C}}_{60}$, and ${\mathrm{K}}_6$${\mathrm{C}}_{60}$ form vacuumlike muonium (${\mathrm{\mu }}^{+}$${\mathit{e}}^{\mathrm{-}}$) with a (6–12)% probability. Observation of coherent spin precession of muonium establishes that all three materials are nonmagnetic and nonconducting at low temperatures. From the temperature dependence of the signals we estimate the electronic band gaps in ${\mathrm{K}}_4$${\mathrm{C}}_{60}$ and ${\mathrm{K}}_6$${\mathrm{C}}_{60}$ to be considerably smaller than in ${\mathrm{C}}_{60}$. The similarity of the muonium centers supports a model in which a muonium atom is caged inside the ${\mathrm{C}}_{60}$ molecule in pure ${\mathrm{C}}_{60}$ or the ${\mathrm{C}}_{60}^{\mathit{x}}$ molecular ion in ${\mathrm{K}}_{\mathit{x}}$${\mathrm{C}}_{60}$.

We analyze the single-particle and collective excitations near the metal to charge-transfer insulator transition, using the slave-boson technique. We show that the Mott transition can be interpreted as a softening of an auxiliary Bose excitation. In the insulating phase the energy of the boson at zero momentum is related to the jump in the chemical potential at zero doping. The dispersion of the collective modes gives rise to the structure of the incoherent Hubbard bands. A similar picture holds for the single-band Hubbard model.