Scanning-tunneling microscopy (STM) images of isolated Cu-phthalocyanine molecules on a Cu(100) substrate exhibit atomic scale features which agree well with Hückel molecular-orbital calculations. Images which show a molecule atop a measurably corrugated Cu(100) surface, a hopping molecule, packed molecular arrays, and a novel molecular binding site at a Cu step edge further illustrate the potential of STM for molecular observations.

We present the first kinetic analysis specifically applicable to the random sequential adsorption (RSA) process in the intermediate coverage range. Our method is applied to hard disks adsorbing on a flat, uniform surface. Exact analytic expressions are derived for the first three coefficients of a power series for the rate of adsorption as a function of the coverage ⊖. Comparison with computer simulations shows that the third-order expansion describes the RSA process to an accuracy of better than 1% up to a coverage of 30%, i.e., up to 55% of the known jamming limit.

A change from a continuous to a discontinuous variation of physical properties has been observed when decreasing the rate of temperature variation in the incommensurate phase of quartz. This effect has been observed by use of birefringence, and has been shown to be strongly dependent on defect concentration. In analogy with the Portevin-Le Chatelier effect, we explain this behavior on the basis of a nonlinear dependence of the friction force on the velocity of the discommensurations resulting from a coupling with mobile impurities.

The low-frequency ($\nu =10\mathrm{}$ kHz) dielectric constants and hysteresis loops of BCCD have been measured under hydrostatic pressure ($p<\mathrm{}550\mathrm{}$ MPa) and at varying temperatures ($115 \mathrm{K}<T<\mathrm{}260\mathrm{} \mathrm{K}$). Several new pressure-induced commensurate and incommensurate phases have been detected and interpreted using the anisotropic next-nearest-neighbor Ising model. Structure branching processes with similar topology in different regions of the phase diagram have been observed. The existence of a Lifshitz point in BCCD is suggested.

A new dislocation source has been observed for the first time in ${\mathrm{Ge}}_x{\mathrm{Si}}_{1-x}/\mathrm{Si}$ strained epitaxial layers. Transmission electron microscopy reveals that strain relaxation at the "critical thickness" in low-mismatch Ge-Si alloys can occur through the emission of glissile dislocations from $\frac{1}{6}〈114〉$ stacking faults. A novel mechanism is proposed to explain the observations whereby the $\frac{1}{6}〈114〉$ boundary dislocation of a stacking fault dissociates (in one of two ways) to emit a $\frac{1}{2}〈110〉$ glissile dislocation, which then bows out under the applied stress to form a loop. As for a Frank-Read source, closure of the propagating glissile loop regenerates the original extended defect.

We have studied two-dimensional and three-dimensional Co${\mathrm{Si}}_2$ epitaxial layers on Si(111) by polarization-dependent surface extended x-ray-absorption fine structure on the Co $K$ edge (7707 eV). The Co interface atoms are coordinated with eight Si atoms, as in bulk Co${\mathrm{Si}}_2$, with an interface bond length of 2.35(0.03) Å. Ultrathin three-dimensional Co${\mathrm{Si}}_2$ layers are 2.5% contracted in the direction perpendicular to the interface.

The $\frac{1}{f}$ resistance noise of thin Bi films of lateral dimensions 1-10 μm increases at low temperatures approximately as $T^{-1\mathrm{}}$, and the noise at 1 K is larger than at room temperature. The noise magnitude is reduced by a factor of 2 above a temperature-dependent characteristic magnetic field. These phenomena demonstrate that below liquid-nitrogen temperature the $\frac{1}{f}$ noise in a weakly disordered metal arises from defect-mediated quantum interference of conduction electrons.

A combination of superconducting integrated circuits was used to construct a very sensitive magnetooptic microsusceptometer for observations of the optically induced magnetization in ${\mathrm{Cd}}_{1-x}{\mathrm{Mn}}_x\mathrm{Te}$ multiple quantum wells. Spin-polarized electrons and holes are created optically, and the quantum mechanically localized wave functions of the carriers then serve as microscopic probes of the magnetic behavior. Both the magnitude and the picosecond dynamics of the magnetic response have been studied and reveal the effects of carrier quantization.

The quantum Ising model in a transverse field with couplings following the Fibonacci sequence is considered. Exact analytical results for the critical line, energy gap, and ground-state singularity are presented. The main features of the multifractal structure of the Cantor-set energy spectrum are discussed.

Thin Fe films on Au(100)—including one monolayer—exhibit long-range ferromagnetic order. The temperature dependence of the magnetization, as measured with spin-polarized low-energy electron diffraction and spin-polarized secondary electron emission, shows a second-order phase transition at a thickness-dependent Curie temperature. The critical exponent $\beta$ for (1-3)-monolayer-thick films is 0.22±0.05, independently of film thickness.

The inelastic-neutron-scattering technique was used to measure the magnetic excitation spectrum of ${\mathrm{Tb}}^{3+}$ dimers in ${\mathrm{Cs}}_3$${\mathrm{Tb}}_2$${\mathrm{Br}}_9$. Between 2 and 3 meV four inelastic transitions are observed which exhibit a different behavior of intensity as a function of momentum transfer. This allows an unambiguous identification of the four types of dimer excitations and, in turn, a direct determination of both the nature and the magnitude of the exchange interaction: It is isotropic with $\mathcal{J}=-0.0049\mathrm{}$ meV.

The Abrikosov flux lattice is imaged in Nb${\mathrm{Se}}_2$ by tunneling into the superconducting gap edge with a low-temperature scanning-tunneling microscope. The tunneling conductance into a single vortex core is strongly peaked at the Fermi energy, suggesting the existence of core states or core excitations. As one moves away from the core, this feature evolves into a density of states which is consistent with a BCS superconducting gap.

The temperature dependence of the magnetic penetration depth $\lambda$ is determined directly from low-field dc magnetization measurements on single-crystal Y-Ba-Cu-O ($T_c=89.7\mathrm{}$ K, $\Delta T_c=0.2\mathrm{}$ K). The results are consistent with the behavior expected from a BCS ($s$ wave) superconductor.

Using oxygen $K$-edge x-ray-absorption spectroscopy we show that the holes compensating the ${\mathrm{Li}}^{1+}$ impurity charge in ${\mathrm{Li}}_x{\mathrm{Ni}}_{1-x}\mathrm{O}$ are located primarily in the O $2p$ states rather than in the conventionally assumed Ni $3d$ states. These holes are bound to the ${\mathrm{Li}}^{1+}$ impurities forming states in the NiO band gap. We also argue that these O $2p$ holes have a very large antiferromagnetic exchange interaction with neighboring ${\mathrm{Ni}}^{2+}$ ($d^8$) spins, which makes them appear like low-spin ${\mathrm{Ni}}^{3+}$ states in macroscopic magnetic measurements. This is similar to what could be happening in the Cu-based high-$T_c$ superconductors.

We propose a generalization of fully connected neural networks, introducing a nonlinear mechanism of the noise level self-control.

We use an electronic four-level model, optically prepared in a coherent superposition of energy eigenstates, to discuss the dynamics of a measurement process leading to the preparation of pure energy eigenstates. The coupling strength to the environment (test laser) is found to control the speed at which information can be gained. An explicit detection strategy is given which can be evaluated as regards its average error probability. The model helps to clarify the conditions under which axiomatic measurement theory (i.e., the collapse of the wave function) applies; it also gives some clues on the recently revived discussion on "quantum jumps."

Muon spin rotation experiments performed on superconducting ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x\mathrm{Cu}{\mathrm{O}}_4$ samples clearly show that internal magnetic fields coexist at low temperatures ($T<\mathrm{}2\mathrm{}$ K) with superconductivity for $x\le 0.15$. The magnetic fields in the superconducting state are an order of magnitude smaller than the corresponding fields in undoped ${\mathrm{La}}_2$Cu${\mathrm{O}}_4$. The data are discussed in the context of a magnetic pairing mechanism in high-$T_c$ superconductors.

The time evolution of electron localization, migration, and solvation in water and ammonia clusters is investigated via computer simulations. The attachment of an electron to a cold molecular cluster in a diffuse weakly bound surface state, the dynamics of solvation, the nonhopping mechanism of migration leading to the formation of an internally solvated state, and the spectral manifestation of these processes are demonstrated.

The transverse-momentum spectra of lambdas (${\Lambda }^0, {\overline{\Lambda }}^0$) produced in the central region has been measured in $\overline{p}p$ collisions at $\sqrt{s}=1.8\mathrm{}$ TeV at the Fermilab Collider. We find that the average transverse momentum of the lambdas increases more rapidly with center-of-mass energy than that of charged particles, and the ratio of lambdas to charged particles increases as a function of center-of-mass energy.

The excitation of the isovector giant dipole resonance by inelastic scattering of 120-MeV $\alpha$ particles has been studied with the ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}(\alpha , {\alpha }^{\prime }, \gamma ){}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ reaction for $0°\le {\theta }_{{\alpha }^{\prime }}\le 3°$. The $\gamma$-decay branching ratio to the ground state, extracted from the coincidence data, indicates that not more than (12±4)% of the observed singles resonance cross section around 13.6 MeV in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ can be due to isovector dipole excitation.