We describe in detail our observations of a new mode of phase separation process which occurs during the annealing of amorphous Al-Ge alloys. This process is characterized by the growth of circular colonies, linear in time at fixed temperature, and with an activated growth velocity. The colonies consist of a branching Ge polycrystalline core and of a nearly monocrystalline Al outer rim, with deep fjords extending into the interior of the colony. The spatial distribution of the constituents is characterized by a length scale, roughly equal to the thickness of the Al rim, that decays exponentially as the temperature is increased. The Al rim contains a fairly large concentration of Ge atoms. The measured values of the characteristic length scale and of the growth velocity appear to be consistent with the assumption that the growth is controlled by the diffusion of Ge atoms from the surrounding amorphous Al-Ge matrix through the crystalline Al rim.

We present a theory for a new mode of phase separation discovered recently in thin layers of amorphous Al-Ge alloys. Phase separation and crystallization occurs in colonies developing from Al nuclei. Their growth is controlled by diffusion of atomic Ge inside crystalline Al, and by the nucleation and growth of Ge crystallites on the Al-Ge interface. We find that the growth velocity is constant as a consequence of the interaction between the ramified Al-Ge interface and the smooth boundary of the colony with the amorphous phase. Diffusion occurs only in a narrow strip controlled by a length scale related to the width of the Ge dendrites. Solution of the growth equations leads to a velocity selection mechanism as long as the Ge concentration is above a critical threshold. The basic length scale is argued to be controlled by a competition between nucleation and growth of the Ge crystallites.

Fully state-resolved analysis of NO molecules desorbed from an oxygen-covered Ni(100) surface by uv radiation (λ=193 nm) yields the operation of two desorption channels, thermal and nonthermal, via electronic excitation. The latter fraction exhibits as a particular feature pronounced spin-orbit selectivity at low rotational quantum numbers.

We report experimental results for the depression of the superfluid transition temperature ${\mathrm{T}}_{\lambda }$(Q) in ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ by a heat current Q. The data were obtained by use of thermometry with a resolution of 10 nK, and cover the range 0.4≲Q≲10 μW/${\mathrm{cm}}^2$. They can be represented by 1–${\mathit{T}}_{\lambda }$(Q)/${\mathit{T}}_{\lambda }$(0)=(Q/${\mathit{Q}}_0$${)}_{\mathit{x}}$ with ${\mathit{Q}}_0$=568±200 W/${\mathrm{cm}}^2$ and x=0.813±0.012, and are in good agreement with theoretical predictions.

Harmonic resonance, subharmonic and superharmonic entrainment, as well as quasiperiodic behavior are among the effects observed if the catalytic oxidation of CO on a Pt(110) surface is carried out under conditions of stable, self-sustained kinetic oscillations and then subjected to low-amplitude periodic modulation of the oxygen partial pressure.

The phason dispersion relation has been measured in the smectic-${\mathrm{C}}^{\mathrm{*}}$ phase of the ferroelectric liquid crystal p-decyloxybenzylidene-p’-omino-2-methylbutyl cinnamate (DOBAMBC) together with the temperature dependence of the phason and amplitudon excitations, by optical mixing spectroscopy. The overdamped phason was found to be nearly gapless in contrast to crystalline incommensurate systems where the modulation wave is pinned by frozen defects. A theory of light scattering by phasons and amplitudons in ferroelectric liquid crystals has been developed.

The dynamics of protons in hydrogen-bonded quasi one-dimensional networks is described in terms of a diatomic lattice model with a doubly periodic on-site potential. The discrete system is reduced to a continuum double sine-Gordon equation for the protonic part plus an easily solvable differential equation for the heavy part. Its two-component kink solitons correspond to the ionic and Bjerrum defects. The correct response of these solitonic defects to an externally applied electric field makes this system a suitable model for qualitative and quantitative description of the protonic conductivity in hydrogen-bonded networks.

Spinodal decomposition of a critical binary mixture of perdeuterated and protonated polymers has been examined by light scattering. Reduction of the characteristic composition fluctuation length (i.e., scattering peak wave vector) and time, based on independently verified scaling parameters obtained from early-stage linear analyses, fails to collapse the intermediate-stage results onto a universal curve. This is the first demonstrated violation of the universal scaling of time and length during spinodal decomposition.

We propose, and demonstrate with the help of a simple model, that the resistance peaks in the quantum Hall experiments on narrow samples result from the phenomenon of ‘‘resonant reflection,’’ which involves a resonant tunneling of an electron from one extended state to another through localized states. We make a number of predictions which involve the specific nature of the breakdown of the dissipationless transport.

We have used a new technique to measure simultaneously the surface topography and surface potential of current-carrying polycrystalline ${\mathrm{Au}}_{60}$${\mathrm{Pd}}_{40}$ thin films using a scanning tunneling microscope. The variations of the gradients of the surface potential from a macroscopically constant value which are associated with scattering from grain boundaries in these films are observed. We find that the local potential changes abruptly at the boundaries between the grains.

The positron lifetime (PLT) in a thin film of amorphous hydrogenated carbon (a-C:H) was studied by a pulsed positron beam. For the first time the PLT was measured in a layer which is as thin as 100 nm. PLT’s of 400(5) ps for the surface state and 348(3) ps in the volume of the film were obtained. The diffusion length of the positrons was measured to be only 4(1) nm. From these results we conclude that in the specimen investigated at least 3% of the total volume is occupied by micropores about 0.5 nm in diameter which may make possible the diffusion of molecular hydrogen in a-C:H.

We have performed small-angle Rayleigh-scattering measurements in toluene subject to a stationary temperature gradient. The experiments demonstrate the existence of long-range equal-time correlations through a strong enhancement of the thermal fluctuations and they also reveal a negative contribution at short time scales from the viscous fluctuations in agreement with the theoretical predictions. The experiments confirm that both effects vary with (∇T${)}^2$/${\mathrm{q}}^4$, where ∇T is the temperature gradient and q the wave number of the fluctuations.

We have made absolute measurement of the quasiparticle band structure of Na(110) using angle-resolved photoemission. These data show that the occupied band is parabolic but with an 18% narrowing in bandwidth compared to self-consistent band calculations. A simple model calculation of the self-energy correction for a homogeneous electron gas produces good agreement with the data, if a dielectric response beyond the random-phase approximation is included. Experiment and theory are compared for other simple metals.

A transfer-matrix Monte Carlo technique is developed to compute the free energy of three-dimensional, classical Heisenberg ferromagnets. From the free energy of systems with periodic and antiperiodic boundary conditions, helicity moduli are calculated. From these the critical couplings for simple-cubic (sc) and face-centered-cubic lattices are estimated by use of finite-size scaling. For the simple-cubic lattice, the critical dimension of the surface magnetization is estimated with standard Monte Carlo methods, yielding a result in excellent agreement with the ε-expansion work of Diehl and Nüsser.

The orbital magnetoconductance (MC) in the variable-range–hopping (VRH) regime is evaluated by use, for definiteness, of a model proposed by Nguyen, Spivak, and Shklovskii, which approximately takes into account the interference among random paths in the hopping process. Instead of logarithmic averaging which is shown to be inadequate for this case, the MC is obtained by the critical percolating resistor method of Ambegaokar, Halperin, and Langer. The small-field MC is quadratic in H; it is positive deep in the VRH regime and changes sign when the zero-field conductivity is high enough. This behavior (except for the sign change) and the relevant magnetic field scale are in agreement with recent experiments. The calculated MC is always positive for strong fields and is predicted to saturate at sufficiently large fields.

The quasiparticle band structure of the heavy-fermion superconductor ${\mathrm{UPt}}_3$ has been investigated by means of angle-resolved measurements of the de Haas–van Alphen effect. Most of the results are consistent with a model of five quasiparticle bands at the Fermi level corresponding to Fermi surfaces similar to those calculated by band theory. However, as inferred from the extremely high cyclotron masses, the quasiparticle bands are much flatter than the calculated ones. The nature of the observed quasiparticles and their relationship to thermodynamic properties are briefly considered.

Recent NMR studies of the one-dimensional charge-density-wave materials ${\mathrm{NbSe}}_3$ and ${\mathrm{Rb}}_{0.3}$${\mathrm{MoO}}_3$ have reported apparently contradictory results for motional narrowing of the charge-density-wave–induced line broadening. A new theoretical model for charge-density-wave motion based on strong pinning and phase slip is found to produce a detailed and quantitative interpretation of all the NMR experiments reported thus far. New behavior is predicted in ${\mathrm{Rb}}_{0.3}$${\mathrm{MoO}}_3$ which can provide a definitive test of the theory.

Chemically mixed molecular crystals show, similarly to isotopically mixed crystals, percolation phenomena for triplet-excitation energy transport. However, because of strong guest-host interaction, energy disorder in the form of induced energy funnels masks the fractal nature of the percolating guest clusters. The assumption of a spectral dimension of ${\mathrm{d}}_{\mathrm{s}}$=(4/3 for percolation at the critical concentration needs in the present case the introduction of an additional waiting-time distribution for a random-walk process.

A hierarchy of L-state cyclic solid-on-solid lattice models, related to the Andrews-Baxter-Forrester solid-on-solid models, is solved exactly. In addition to the usual anisotropy parameter (spectral parameter) u and the temperaturelike variable (elliptic nome) p, the exact solution admits a phase angle ${\mathrm{w}}_0$ that interpolates between heights. Results for the free energy and local height probabilities are obtained. The exact solution exhibits first-order coexistence manifolds which coalesce at the multicritical point (p=0). For L=3, our results extend Baxter’s results on the three colorings of the square lattice.

We have found that the usual measuring procedure for preselected and postselected ensembles of quantum systems gives unusual results. Under some natural conditions of weakness of the measurement, its result consistently defines a new kind of value for a quantum variable, which we call the weak value. A description of the measurement of the weak value of a component of a spin for an ensemble of preselected and postselected spin-(1/2 particles is presented.