A model system of impenetrable vortex lines with short range interactions is considered on a cylindrical superconducting film with random disorder at a temperature T≥0. The system is dual to spinless fermions in a dynamic random external potential. Replicaton and Bethe ansatz calculations yield a finite charge stiffness for the fermions, which are thus not localized. Some amount of correlation of the disorder appears necessary to produce a vortex-glass phase in the simple model vortex-pin system considered.

Sandpile models with randomized updating rules are studied. The randomness is not quenched, but set dynamically by the dissipation events (avalanches) in the system. Relaxation from fixed updating rules is here a consequence of medium anisotropy and motiviated by the behavior of various driven physical systems. A one-dimensional sandpile model in which the critical slope at a site varies as the process proceeds displays self-organized criticality. The model allows one to build in an internal relaxation mechanism separated from the external driving flux and underlying the noise of the process.

Coherent intermediate scattering functions are measured by dynamic light scattering for several wave vectors around the structure factor peak on metastable colloidal fluids and glasses of hard spherical particles. The results are quantitatively described by a combination of the α and β processes. The scaling laws and factorization property predicted by mode-coupling theory are verified.

Here we study the interplay between wetting and phase separation for a nearly symmetric binary mixture confined in a one-dimensional (1D) or a two-dimensional (2D) capillary. It is found that near the symmetric composition, the hydrodynamics unique to bicontinuous phase separation plays a crucial role in the wetting dynamics and the surface effect is strongly delocalized by the interconnectivity of the phases. The growth rate of the wetting droplet and the thickening rate of the wetting layer are discussed on the basis of the hydrodynamic coarsening. The effect of the dimensionality of the geometrical confinement is also discussed.

A new method for the computation of thermodynamic properties of solid defects is introduced. The free energy of formation of a defect is written as a simple function of a universal crystalline free energy. Computed temperature variations of surface energies are found to be consistent with experiment. The source of the linear term in the low-temperature specific heat of defect materials is revealed. Computed magnitudes of the linear term are found to be in reasonable agreement with experiment for amorphous metals and nanocrystalline Pd.

The contact angle is an important boundary condition needed to predict the shape of menisci. However, its measurement and use under dynamic conditions are not well understood. We have measured the shape of menisci very close to moving contact lines over a suite of geometric shapes for the macroscopic menisci. The excellent agreement between theory and experiment establishes that the proposed boundary condition characterizes only the materials of the system. Implications for the microscopic physics controlling the dynamic contact angles are explored.

Strained epitaxial layers tend initially to grow as dislocation-free islands. Here we show that such islands, as they increase in size, may undergo a shape transition. Below a critical size, islands have a compact, symmetric shape. But at larger sizes, they adopt a long thin shape, which allows better elastic relaxation of the island’s stress. We have observed such elongated islands, with aspect ratios greater than 50:1, in low energy electron microscopy studies of growth of Ag on Si(001). These islands represent a novel approach to the fabrication of ‘‘quantum wires.’’

We study the adsorption of Al on the Si(100) surface by ab initio calculations for a complete range of coverages from an isolated Al adatom up to full surface coverage. Analysis of the energetics of adsorption and the mobility of Al adatoms reveals that the long, one-dimensional strings of Al dimers observed experimentally result from a sequence of reaction steps which can be classified as a surface polymerization. The calculated local density of states (LDOS) of the adsorbed Al row is compared with scanning tunneling microscopy images. The LDOS characteristic of the reaction sites which mediate the polymerization should be observable by scanning tunneling spectroscopy.

The asymmetric or symmetric nature of the dimer adatom arrangement on reconstructed Si and Ge (001) surfaces is still controversial. There has not been a direct quantitative determination of the asymmetry. Using x-ray standing waves we have directly measured the asymmetry of Ge dimers on the Si(001) surface as 0.55±0.02 Å. Our results unequivocally rule out the possibility of symmetric dimers. At elevated temperatures the dimer asymmetry decreases, raising the possibility of a high temperature asymmetric to symmetric phase transition on the (001) surfaces.

We have performed positron lifetime experiments under monochromatic illumination in undoped semi-insulating GaAs. A negative vacancy, identified as the Ga vacancy, is observed in darkness. Illumination with 1.42 eV photons below 150 K reveals another type of vacancy, identified as the As vacancy. The As vacancy has a negative charge state above the ionization level at 50±5 meV below the conduction band. This level offers a microscopic explanation to the optical near-band-edge absorption. The concentrations of both Ga and As vacancies are between ${10}^{15}$ and ${10}^{16}$ ${\mathrm{cm}}^{\mathrm{-}3}$.

We measured low temperature conduction characteristics of amorphous indium/indium-oxide composite films deep in the insulating regime. Upon lowering temperature, resistance crosses over from an Efros-Shklovskii variable-range-hopping conduction to a simple activation conduction, with parameters in good agreement with the picture of hardening of a parabolic Coulomb gap near the Fermi level. In contrast to the previous observations in magnetic materials, however, the hard gap in our films is extremely insensitive to a magnetic field, which strongly indicates a nonmagnetic nature of the hard gap.

Spin-resolved inverse photoemission measurements on Ni(111) reveal a crystal-induced surface state close to the Fermi level that is partly occupied around the Γ¯ point of the surface Brillouin Zone. This finding together with an observed splitting of about 100 meV between spin-up and spin-down states identifies this state as a truly magnetic state contributing to the surface magnetic moment of Ni(111). A photon polarization analysis shows that hte state has ${\mathrm{\Lambda }}_1$ symmetry at Γ¯, therefore being derived from the p-like ${\mathrm{L}}_{2\prime }$ bulk state. © 1993 The American Physical Society

We solve the quasiclassical equations of superconductivity self-consistently for a lattice of interacting flux lines and calculate the local density of states at a flux-line center. For strongly interacting flux lines, with a nearest-neighbor distance d smaller than about 7 coherence lengths, we find an oscillatory behavior of the density of states as a function of energy. These oscillations increase in magnitude with decreasing d and should be observable by means of scanning-tunneling-microscope experiments. We analyze the physical origin of this behavior in terms of the direction dependence of the quasiparticle states in a dense vortex lattice.

A magnetic susceptibility which decreases with decreasing temperature is observed in all Cu${\mathrm{O}}_2$ based superconductors with less than optimal doping. We propose that in ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x\mathrm{Cu}{\mathrm{O}}_4$ this is due to spin density wave ordering which is prevented by the low spatial dimensionality, while in Y${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{6.6}$ it is due to the interplay between antiferromagnetic fluctuations within a plane and singlet pairing of electrons between nearest neighbor planes.

We have investigated the magnetic response of untwinned single crystals of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ at millikelvin temperatures using a Bi thin film magnetometer of micron dimensions. Below T=0.8 K, the magnetization relaxation rate S crosses over from thermally activiated to quantum behavior. Above a sharply defined and strongly temperature-dependent threshold field, S disappears altogether. In concert with the vanishing magnetization relaxation, discrete steps appear in the magnetic hysteresis B(H), each of which corresponds to the ‘‘stick-slip’’ motion of ${10}^3$ vortices under the magnetometer.

We have measured the dynamic susceptibility of polycrystalline rhodium foils down to 280 pK and up to -750 pK. These record-low and -high nuclear spin temperatures were reached by adiabatic demagnetization using initial polarizations of 83 and -60%. At T>0, the static susceptibility, integrated from NMR spectra, displays an antiferromagnetic Curie-Weiss law, with θ=-1.8±0.3 nK. At T<0, a crossover from ferro- to antiferromagnetic tendency is found around -6 nK. We obtain ${\mathit{J}}_{\mathit{n}\mathit{n}}$/h=-17±3 Hz and ${\mathit{J}}_{\mathrm{nnn}}$/h=10±3 Hz if only nearest and next nearest neighbor interactions are assumed.

Levinson’s theorem for the Dirac equation is known in the form of a sum of positive and negative energy phase shifts at zero momentum related to the total number of bound states. In this Letter we prove a stronger version of Levinson’s theorem valid for positive and negative energy phase shifts separately. The surprising result is that, in general, the phase shifts for each sign of the energy do not give the number of bound states with the same sign of the energy (in units of π), but instead are related to the number of bound states of a certain Schrödinger equation, which coincides with the Dirac equation at zero momentum.

An extension of the Parker bound on the flux scrF of magnetic monopoles leads to a stronger bound than obtained previously. The survival and growth of a small galactic seed field requires scrF≤${10}^{\mathrm{-}16}$(m/${10}^{17}$ GeV) ${\mathrm{cm}}^{\mathrm{-}2}$ ${\mathrm{s}}^{\mathrm{-}1}$ ${\mathrm{sr}}^{\mathrm{-}1}$. This new limit rules out the possibility that monopoles much lighter than ${10}^{17}$ GeV/${\mathit{c}}^2$ can provide the closure density of the Universe.

We present the first measurement of the left-right cross section asymmetry (${\mathit{A}}_{\mathit{L}\mathit{R}}$) for Z boson production by ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ collisions. The measurement was performed at a center-of-mass energy of 91.55 GeV with the SLD detector at the SLAC Linear Collider which utilized a longitudinally polarized electron beam. The average beam polarization was (22.4±0.6)%. Using a sample of 10 224 Z decays, we measure ${\mathit{A}}_{\mathit{L}\mathit{R}}$ to be 0.100±0.044(stat)±0.004(syst), which determines the effective weak mixing angle to be ${\sin }^2$${\mathrm{\theta }}_{\mathit{W}}^{\mathit{e}\mathit{f}\mathit{f}}$=0.2378 ±0.0056(stat)±0.0005(syst).

An upper limit on the branching ratio for the decay $K^{+}\to {\pi }^{+}\nu \overline{\nu }$ is set at 7.5 × ${10}^{-9\mathrm{}}$ (90% C.L.) using the kinematic region above the $K_{\pi 2}(K^{+}\to {\pi }^{+}{\pi }^0)$ peak. When combined with our result from below the $K_{\pi 2}$ peak, we obtain the limit 5.2 × ${10}^{-9\mathrm{}}$. An upper limit of 1.7 × ${10}^{-9\mathrm{}}$ is also found on the branching ratio for decays of the form $K^{+}\to {\pi }^{+}{X}^0$ where $X^0$ is any massless, weakly interacting neutral particle. Limits are also set for cases where $M_{X^0}>0\mathrm{}$.