A growth process is characterized by the growth-site probability distribution $\frac{\left\{p_i\right\}}{i\epsilon \Gamma }$, where $p_i$ is the probability that site $i$ on the surface of the cluster becomes part of the aggregate. Equations for the $p_i\text{'}\mathrm{s}$ are solved numerically for diffusion-limited aggregation and the dielectric breakdown models by the standard Green's-function technique, and moments of the distribution are calculated indicating that a hierarchy of independent exponents is required to describe the critical behavior. The absence of a linear relation among the exponents is indicative of a nonconventional scaling for the growth probability distribution.

We report the first observation of a class of new reconstructions on clean silicon (111) surfaces. The surfaces are prepared by a combination of laser and thermal annealing and the new structures are studied with a tunneling microscope. $c-(4\mathrm{}\times 2)\mathrm{and}(2\mathrm{}\times 2)$ regions populate the ordered parts of the surface directly after laser annealing. Subsequent partial thermal anneals result in a surface containing (5×5), (7×7), (9×9), and other intermediate structures. These observations' bearing on the connection between germanium and silicon reconstructions is discussed.

The amplitude decay of surface profiles in [1¯10] and [001] directions on (110) surfaces of Pt and Cu was compared and found to be purely exponential except for the Pt(100) [001] case. The latter is also the direction of the (1×2) reconstruction typical for clean Pt(110). The nonexponential decay rate observed for Pt(110) [001] was theoretically duplicated by incorporation of a large anisotropy in the surface energy of about 10% into the decay kinetics. Thus, a common cause for the (1×2) reconstruction and the nonexponential profile decay along the [001] azimuth may be the large anisotropy in the surface energy of Pt.

We have observed an anomaly in the attenuation and phase velocity of zero sound in superfluid ${}_{}{}^3{}_{}{}^{}\mathrm{He}-A$ at a temperature experimentally unresolvable from the $A_2$ transition. The feature is present at all magnetic fields and frequencies for sound propagated perpendicular to the applied field H, but it disappears for sound traveling along H. We discuss this phenomenon in terms of a first-order transformation between dipole-locked and dipole-unlocked planar textures driven by the thermodynamic second-order phase transition at $T_{A_2}$. We also report the first observed splitting of the normal flapping mode in a magnetic field.

We have explored some of the consequences of the nearly metamagnetic model of liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ due to Bedell and Sanchez-Castro. The most interesting result is for the superfluid transition. The superfluid phase shows a reentrant behavior with the transition temperature reaching a maximum of ∼ 14 mK at 25 bars and 35% polarization. We propose an experimental procedure for reaching this region of the phase diagram and discuss a number of experiments to explore the reentrant behavior.

The dielectric function of a water-oil microemulsion was studied at a microwave frequency of 10 GHz where the total dielectric response is dominated by the water component. An effective-medium analysis revealed that the properties of micellar water in a microemulsion change towards those of bulk water as the cloud-point temperature is approached. No universal critical exponents were found, in contrast to previous low-frequency and light-scattering data.

The charge relaxation rate ${\Gamma }_c$ of intermediate-valence compounds is identified experimentally by the different behavior of the phonon-mode frequencies for $\hslash \omega >>{\Gamma }_c$ and $\hslash \omega \lesssim {\Gamma }_c$. This classification yields a systematic understanding of the occurrence or absence of phonon anomalies in all intermediate-valence compounds investigated so far. A temperature dependence of ${\Gamma }_c$ could be determined in the case of ${\mathrm{Sm}}_{0.75}$${\mathrm{Y}}_{0.25}$S.

Systems displaying long-period, uniaxial, commensurate, modulated phases are analyzed for $d>\mathrm{}2\mathrm{}$ dimensions in terms of pair, triplet, quadruplet,... interactions between domain walls in an underlying ordered phase. The axial next-nearest-neighbor Ising (ANNNI) and three-state chiral clock (C${\mathrm{C}}_3$) models with coordination numbers $q_i$ are treated as examples, revealing new lowtemperature phases. The phase diagrams in the mean-field limit, $q_i\to \infty$, agree with the small-$q_i$ results for the ANNNI but not for the C${\mathrm{C}}_3$ model, in which a quasitricritical point appears when $q_1>~4$.

A close analogy is pointed out between dyons (particles with electric and magnetic charge) in grand-unified theories and solitons in antiferromagnetic chains. For nonzero topological angle $\theta$, dyon electric charges are noninteger: $q=(n+\frac{\theta }{2\pi })e$. An analogous phenomenon occurs in antiferromagnets with alternating interactions.

Two percolation models for electrical breakdown in quenched random media, a fuse-wire network and a dielectric network, are introduced and studied. A combination of Lifshitz and scaling arguments leads to a size dependence given by $\frac{V_b}{L}\sim \frac{a\left(p\right)\mathrm{}}{\mathrm{}[1+b(p\left)\mathrm{}{\left(\ln L\right)}^{\beta }\right]}$, where $\frac{\beta =1\mathrm{}}{\mathrm{}(d-1\mathrm{})\mathrm{}}$ for the fuse network and $\beta =1\mathrm{}$ for the dielectric network. Simulations support this hypothesis in the 2D fuse network. We argue that any finite fraction of quenched defects qualitatively reduces the breakdown strength of a wide variety of electrical and mechanical systems in both two and three dimensions.

A model is presented in which a semiconductor crystal contains an infinite metallic donor cluster as well as shallow donors which do not have close neighbors thus supporting effectively localized electronic states. The average carrier concentration in the infinite cluster is greater than the crystal-average electron concentration. The model is applied to the Hall effect below the magnetic-field-induced metal-insulator transition in ${\mathrm{Hg}}_{1-x}{\mathrm{Cd}}_x\mathrm{Te}$ and InSb.

Cooled, extrinsic GE that is voltage biased to produce a spontaneous current oscillation exhibits frequency locking, quasiperiodicity, and chaos when driven with a sinusoidal voltage. The low-frequency current power spectrum at the transition from quasiperiodic to chaotic behavior agrees in detail, both in frequency and in amplitude, with the calculated universal spectrum of the circle map. The large dynamic range (> 70 dB) and the convenient frequency (10 kHz) of the spontaneous oscillation make this an excellent system for testing the predictions of theory.

Inverse photoemission spectra of xenon layers adsorbed on Au(110) have been recorded. The unoccupied levels of xenon exhibit layer-dependent peak shifts to higher energies. The $6s$ level of the second xenon layer is shifted by 0.65 eV relative to the monolayer energy, with the $6p$ level exhibiting a 0.85-eV shift. These shifts are related to the image-charge screening of the negative-ion inverse-photoemission-spectra final states. This observation demonstrates the influence of screening in inverse photoemission, and provides a test of the different conflicting models put forward in explanation of such shifts.

The electric quadrupole hyperfine interaction at Cu (100) surfaces has been detected at isolated ${}_{}{}^{111}{}_{}{}^{}\mathrm{In}$ probe atoms by use of the perturbed $\gamma \gamma$ angular correlation technique. The electric-field-gradient tensor at $T=295\mathrm{}$ K was found to be axially symmetric with a strength of $\left|V_{\mathrm{zz}}\mathrm{}\right|=1.0\left(2\mathrm{}\right)\mathrm{}\times {10}^{18}$ V/${\mathrm{cm}}^2$ and the symmetry axis perpendicular to the (100) surface. A linear temperature dependence of the electric field gradient was observed. These findings support the assumption of highly symmetric surface sites as positions for the ${}_{}{}^{111}{}_{}{}^{}\mathrm{In}$ probes.

The magnetic susceptibility, specific heat, and electrical resistance of ${\mathrm{U}}_{1-x}{\mathrm{Th}}_x{\mathrm{Pt}}_3$ have been studied for $x$ between 0.01 and 0.10 at temperatures between 1.5 and 20 K. In addition to the well known heavy-fermion behavior, at 6.5 K a Fermi-surface instability is observed and it is concluded that the superconducting ground state in U${\mathrm{Pt}}_3$ is replaced by a spin-density wave. This result demonstrates the delicate balance between superconductivity and magnetism in U${\mathrm{Pt}}_3$.

We report a detailed calculation of the photoemission spectra of Na for electrons emitted normal to the (110) surface. The experimental results of Jensen and Plummer have been taken as an indication that the conduction band of Na is severely distorted and hence that a charge-density wave exists in the system. Our calculation confirms just the opposite, i.e., that the band is not strongly distorted from a free-electron band. The calculation is able to reproduce the experimental data closely; it also predicts an angle dependence of the spectra—a feature which needs to be examined experimentally.

We present a new characterization method for traps at the interfacial layer of Schottky contacts. This method is based on ac-admittance measurements and a new trap transistor model which quantitatively explains the measured ac behavior as well as the dc characteristics. In particular we propose the ac current across the interface to consist of capacitive as well as of conductive parts. We apply the analysis to Au/GaAs Schottky contacts and find a weak energy dependence for the density of interface states in the band gap of GaAs.

The Boltzmann equation allows a study of the effect of electron-electron scattering on the anisotropy of the electron distribution in a large electric field. An effective electron-electron scattering rate $\frac{1}{{\tau }_{\mathrm{ee}}}$ relates how the quadrupole moment of the distribution in velocity space relaxes, lower moments being preserved by electron-electron scattering. We report (1) calculated distribution functions and (2) the density and drift-velocity dependence of $\frac{1}{{\tau }_{\mathrm{ee}}}$ for realistic electron-electron scattering.

It is shown that in simple three-dimensional flows there are uncountably many different codimension-2 scenarios for the onset of chaos. We analyze these scenarios via one-dimensional Poincaré maps, and show how to construct renormalization groups to obtain new universal results. Comparisons with numerical studies are given.

It is shown that energy should be quantized if there exist cosmic spinning strings. Quantization of energy arises naturally from the fact that the wave function must be single valued in the gravitational field of a spinning string. This effect arises when the vortexlike vacuum configurations carry constant nonzero angular momentum per unit length. Spinning strings occur naturally in spontaneously broken grand unified theories. A limit on $J$ coming from the upper limit of the photon mass is presented. The analogy with quantization of energy in the presence of gravitational magnetic mass is established.