We observe linear and nonlinear features of a strong plasma/magnetic field interchange Rayleigh-Taylor instability in the limit of large ion Larmor radius. The instability undergoes rapid linear growth culminating in free-streaming flute tips.

In the Joint European Torus the ablation of injected pellets produces a striking resonance effect when the pellets reach surfaces with q values 1 and (3/2. Subsequently, structures with mode numbers m=1,n=1 and m=3,n=2 are observed with the soft-x-ray cameras for up to 2 s as compact snakelike perturbations. These structures, which persist through several sawtooth collapses, give information on the radii of the q=1 and q=(3/2 surfaces and the q-profile evolution. The observations can be explained by the formation of magnetic islands.

We report a medium-energy ion-scattering study of the (1×2) reconstruction of the Ag(110) surface induced by submonolayer amounts of K. A qualitative comparison between ion-scattering data from the clean and K-covered surfaces shows that the (1×2) periodicity is caused by a missing-row reconstruction of the Ag substrate. Computer simulations support this conclusion and provide detailed information on the atomic positions. Our observations support a recent model by Heine and Marks explaining surface relaxation and reconstruction in terms of the occupation of s-p and d electronic levels.

We have fabricated wire networks in the form of triangular arrays of third-order Sierpinski gaskets and percolation arrays on square lattices. For the gaskets the superconducting phase boundary, ${\mathrm{T}}_{\mathrm{c}}$(H), exhibits a clear crossover between the homogeneous and inhomogeneous (fractal) regimes. This is formally equivalent to the phonon-fracton crossover. Surprisingly, the random, square-lattice percolation networks, which are expected to exhibit a similar crossover, seem to behave in a manner characteristic of two-dimensional systems, independent of length scale.

The dense radial structure is a distinct morphology which develops in many diffusive pattern-forming systems. We propose the first model to explain the stability of this structure. Stability arises in this model from the resistivity of the growth channels, which has been neglected in previous analyses. We also report excellent agreement between the predictions of our model and experimental results from two-dimensional electrochemical deposition.

Single-photon ionization thresholds are reported for mercury clusters with up to 70 atoms prepared in a supersonic beam. The size dependence of the ionization potentials provides the first direct experimental evidence that a heretofore undetected size-dependent gradual transition from van der Waals–type to metallic properties occurs for mercury clusters in the size range between 20 to approximately 70 atoms.

The thermodynamic perturbation scheme so successful for classical-liquid equations of state is applied to the ground-state energy of a many-boson system interacting pairwise via the Lennard-Jones intermolecular potential. The ensuing density and attractive-coupling double expansion for the energy is series analyzed with Padé techniques, as well as generalizations thereof. Results through sixth order compare with Green’s-function Monte Carlo simulations at the 1% level of accuracy.

We consider the time evolution of two Ising systems that differ at time t=0 in the orientation of only one spin. The detailed time development is calculated from two algorithms: (i) Glauber dynamics and (ii) Q2R dynamics (a deterministic cellular automaton). We find that for both algorithms spreading of ‘‘damaged regions’’ is greatly hindered below a threshold temperature ${\mathrm{T}}_{\mathrm{s}}$ (or energy), which agrees numerically with the Curie point. For Glauber dynamics ${\mathrm{T}}_{\mathrm{s}}$ is found to be a sharp phase transition point; for Q2R dynamics we find a kinetic slowing down which is reminiscent of a (spin-) glass transition.

Scanning tunneling microscope images showing the lateral registration of the Ag/Si(111)(√3 × √3 )R30° structure relative to the Si(111)7×7 structure demonstrate that protrusions are observed at threefold hollow sites. These protrusions can thus be associated with Ag atoms in the honeycomb structure but not with Si atoms in the embedded trimer structure. Images of domain boundaries and steps also suggest that the top double layer of Si is intact, in disagreement with another recent model.

The role of spin-exchange processes in (quasi-)elastic electron scattering is investigated by measurement of the changes in polarization of a spin-polarized electron beam scattered in specular geometry from Ni(110) and Ni(110)O(2×1) over an energy range of 5 to 30 eV. Concurrently measuring the scattered intensity as a function of primary spin polarization yields the spin-dependent reflection coefficients. These reflection coefficients entirely account for the changes in polarization. Therefore, it is concluded that spin-exchange processes are negligible (<=3%) in the elastic channel.

The fundamental relationship between radiative lifetime and spectral linewidth of free excitons is demonstrated theoretically and experimentally for quasi 2D excitons in GaAs/AlGaAs quantum wells.

In this paper we present results of electron mobility measurements on AlGaAs as a function of hydrostatic pressure which show the influence of resonant scattering by the central-cell potential of silicon. This is, we believe, the first direct observation of resonant impurity scattering in semiconductors.

Magnetization measurements on a very dilute Au-V alloy yield evidence for the existence of a nontrivial power-law scaling at low temperatures. The n-channel Kondo model fits the data with ${\mathrm{T}}_{\mathrm{K}=60\mathrm{}}$ K and n=5 for an impurity spin S=(3/2. .AE

To determine the phase velocity of the charge-density-wave (CDW) voltage noise and ${}_{}{}^{87}{}_{}{}^{}\mathrm{Rb}$ NMR spectra at an electric field of about 15$E_T$ were measured together with I-V characteristics on a ${\mathrm{Rb}}_{0.3}$${\mathrm{MoO}}_3$ crystal between 40 and 60 K. NMR spectra are reproduced by means of a velocity distribution determined by the noise spectrum. A ratio of the average noise frequency to $j_{\mathrm{CDW}}$ between 12.8 and 17.7 kHz/A⋅${\mathrm{Cm}}^{\mathrm{-}2}$ and a ratio of the average local-field oscillation frequency to $j_{\mathrm{CDW}}$ of 11±1 kHz/A⋅${\mathrm{cm}}^{\mathrm{-}2}$ are found, values close to 12.5 kHz/A⋅${\mathrm{cm}}^{\mathrm{-}2}$ from the electron density. NMR sidebands show that local-field oscillations are coherent.

The f-sum rule, relating effective masses to oscillator strengths, is extended to semiconducting superlattices and applied to GaAs-(Ga,Al)As and HgTe-CdTe. This novel approach is implemented analytically by use of the envelope-function approximation to calculate both parallel and perpendicular masses and is used to account for their difference physically. Agreement with experiment is excellent, but in HgTe-CdTe only if the valence-band offset is small.

A tunneling escape rate 1/${\mathrm{\tau }}_{\mathrm{T}}$ of electrons from a single quantum well through thin barriers was successfully determined by measurement and analysis of the lifetime ${\mathrm{\tau }}_{\mathrm{e}}$ of electrons generated in 6.2-nm GaAs single quantum wells by a picosecond laser pulse. The measured ${\mathrm{\tau }}_{\mathrm{e}}$ was found to decrease systematically as the AlAs barrier thickness ${\mathrm{L}}_{\mathrm{B}}$ was reduced. The ${\mathrm{\tau }}_{\mathrm{e}}$ for ${\mathrm{L}}_{\mathrm{B}}$<4 nm was found to agree very well with the lifetime ${\mathrm{\tau }}_{\mathrm{T}}$ predicted from the energy width of the resonance transmission. Irrelevance of coherence versus incoherence in the tunneling escape process is also pointed out.

We formulate the current-density–functional theory for systems in arbitrarily strong magnetic fields. A set of self-consistent equations comparable to the Kohn-Sham equations for ordinary density-functional theory is derived, and proved to be gauge invariant and to satisfy the continuity equation. We prove that the exchange-correlation energy functional ${\mathrm{E}}_{\mathrm{xc}[\mathrm{n}}$,${\mathrm{j}}_{\mathrm{p}}$] [n(r) is the density and ${\mathrm{j}}_{\mathrm{p}}$(r) is the ‘‘paramagnetic’’ current density] depends on the current via the combination ν(r)=∇×${[\mathrm{j}}_{\mathrm{p}}$(r)/n(r)]. An explicit formula for ${\mathrm{E}}_{\mathrm{xc}}$ is derived, which is local in ν(r).

Neutron scattering demonstrates the coexistence of antiferromagnetic order and spin-glass in the Ising system ${\mathrm{Fe}}_{\mathrm{x}}$${\mathrm{Mn}}_{1\mathrm{-}\mathrm{x}}$${\mathrm{TiO}}_3$ for x=0.33, 0.60, and 0.65. The behavior of the diffuse intensity as well as the inverse correlation length κ as functions of Fe ion concentration x strongly suggests that there exists a phase boundary between the coexistence phase and the pure spin-glass phase. Thus the phase below the Almeida-Thouless line in an Ising spin-glass system should be distinguished from the pure spin-glass phase.

The absence of a detectable γ-ray emission from SN1987A following neutrino burst from this source has closed the window left by accelerator experiments and by previous astrophysical and cosmological observations for the existence of heavy neutrinos whose mass is less than 100 MeV and which are mixed with ${\nu }_3$.

Galaxy and structure formation in a neutrino-dominated universe with cosmic strings is investigated. Strings survive neutrino-free streaming to seed galaxies and clusters. The effective maximum Jeans mass is about 1.5×${10}^{14}$$n_{50}^{\mathrm{-}4}$$M_{\odot }$, lower than in the adiabatic scenario. Hence cluster formation is only marginally different from that in the cold-dark-matter and strings model, but galaxy masses are lower. The mass spectrum of galaxies is flatter than with cold dark matter, and the density profile about an individual loop is less steep, in better agreement with observations.