The excitation spectra of compressional modes of ${}_{}{}^4{}_{}{}^{}\mathrm{He}_{\mathit{N}}^{}{}_{}{}^{}$, N=20, 70, and 240, clusters at 0 K are calculated by treating the cluster as a quantum liquid drop. The spectrum of N=240 strongly resembles that of liquid helium with a visible roton structure, while for N=20 no roton minimum is seen and N=70 shows a weak minimum. Implications of these findings for superfluidity in helium clusters are discussed.

It is shown that the superfluid turbulence arises as a convective, not an absolute, instability. A continuous source of macroscopic quantized vortices is therefore required, not only to initiate the turbulence, but also to keep the vortex tangle alive. It is demonstrated that a streamwise-pinned, remanent vortex at the channel inlet can act as the fluid dynamical analog of a phase-slip center, injecting vortex filaments into the flow at a steady rate. Several such vortex mills in tandem are sufficient to initiate and sustain the turbulent state.

The transmission of phonons with frequencies above 140 GHz across a solid-solid interface is examined by phonon imaging. Heat pulses transmitted through varying thicknesses of MgO films on Ge clearly display total internal reflection beyond a critical angle and frustrated total internal refraction when the film thickness is comparable to the phonon wavelength. These manifestations of Snell’s law demonstrate the specular (i.e., not diffuse) refraction expected from acoustic mismatch theory, in contrast to most earlier measurements.

One-phonon ionization of donors in germanium via intervalley scattering by slow TA phonons at the X point of the Brillouin zone is demonstrated by the stress dependence of phonoconductivity. Superconducting aluminum junctions are used as tunable quasimonochromatic phonon sources up to these extreme frequencies. The ionization probability is found to be increased when donor levels associated with stress-shifted higher valleys of the conduction band cross the lowest valley(s).

We report the first observation of a novel growth mode in a metal/metal epitaxy system: bilayer formation in Au overlayers grown on Ag(110). By using medium energy ion scattering to determine the morphology and structure of the overlayers, we find direct evidence that bilayers form spontaneously over a wide range of coverages. We discuss the possible causes of this unusual growth behavior.

We have performed the first calculation of the activation energy for self-diffusion in a liquid metal which contains no adjustable parameters. The calculation uses the local-density-functional theory combined with the Car-Parrinello technique for molecular-dynamics simulation. The coefficient of self-diffusion agrees well with the experimental value and fits the form D=${\mathit{D}}_0$ i/rexp(-${\mathit{E}}_{\mathit{a}}$/${\mathit{k}}_{\mathit{B}}$T) with ${\mathit{E}}_{\mathit{a}}$=0.099 eV, ${\mathit{D}}_0$=0.84×${10}^{\mathrm{-}3}$ ${\mathrm{cm}}^2$/sec, compared to the most recent experimental values of ${\mathit{E}}_{\mathit{a}}$=0.096 eV, ${\mathit{D}}_0$=0.86×${10}^{\mathrm{-}3}$ ${\mathrm{cm}}^2$/sec.

A variable-temperature scanning tunneling microscope has been used to elucidate the structure of the nearly commensurate (NC) charge-density-wave (CDW) phase in 1T-${\mathrm{TaS}}_2$. Between 230 and 350 K the NC CDW phase consists of a hexagonal array of commensurate domains separated by diffuse domain walls where the CDW phase and amplitude change. The average domain period and size increase continuously as the temperature is lowered over this range. Microscopic details of this growth process are discussed.

We test the implicit prediction of a recent classical model that transport anomalies in ballistic multiprobe conductors—the last plateau, quenching, and the negative bend resistance—should scale with Fermi momentum, ${\mathit{p}}_{\mathit{F}}$. Data from junctions defined by adiabatic lateral potentials (having corners with radii of curvature ${\mathit{r}}_{\mathit{J}}$>ħ/${\mathit{p}}_{\mathit{F}}$) qualitatively scale classically; departures observed are attributed to momentum-memory loss from random scattering. With more abrupt (square-cornered) junctions, however, nonclassical ${\mathit{p}}_{\mathit{F}}$ dependence emerges.

The results of a new experiment, which records transient, pulsed-laser-induced surface photovoltages by following photoemission shifts measured with synchrotron radiation, are reported. Comparison of the surface photovoltage decays with numerical simulations reveals large surface recombination rates for a variety of Si(111) surface preparations. The space-charge layer near the surface is found to govern the surface and bulk carrier concentrations to a remarkable extent, particularly when band bending is large.

It is shown that an orbital-polarization correction to a spin-polarized band-structure calculation leads to an insulating gap for CoO, in sharp contrast to a standard band calculation. Orbital-polarization instabilities, though, are not found for FeO and ${\mathrm{La}}_2$${\mathrm{CuO}}_4$.

Lattice U(1) instantons in 2+1 dimensions have no fermion zero modes and do not break U(2n) flavor symmetry. Nevertheless, instantons in the presence of massless fermions interact via logarithmic potentials. These results are applied to the ‘‘flux’’ phase of a SU(n) antiferromagnet and the possibility of a transition from a gapless spin-liquid state to Néel order as n decreases from 4 to 2 is discussed.

We investigate the Fermi-liquid parameters and the superconducting instabilities of the t-J model using a systematic large-N expansion. We compare our results with the predictions of the Brinkman-Rice picture. The leading superconducting instability is in the d-wave channel and has cos${\mathit{K}}_{\mathit{x}}$-cos${\mathit{K}}_{\mathit{y}}$ symmetry and increases with doping.

The exact Schrödinger equation involving a modified Fröhlich Hamiltonian used in Davydov soliton theory is formulated in terms of unitary time displacement and phonon coordinate displacement operators. Use is made of the sparse nature of the resulting matrix operators to develop an algorithm for vector processing on the Cyber 205 supercomputer. All numerical calculations lead us to conclude that the Schrödinger equation does not support the existence of the Davydov soliton as a persistent localized entity.

Considering the ι(1460) to be the physical glueball G and to mix with η’, we then find the mixing angle to be restricted to 0.15>sin${\theta }_2$>-0.43 from the data of ${\pi }^0$,η,η’→2γ and the upper bound on ι(1460)→2γ. The transition matrix element for $K_L$→$G^0$ (bare glueball) is also computed (and found to be comparable to that for $K_L$→${\pi }^0$). These permit the glueball contribution to $K_L$→2γ and & to be significant. Finally, for large mixing angles, the decay of $D_s^{+}$ into a glueball is sizable, e.g., B($D_s^{+}$→ι(1460)${\pi }^{+}$) can be as large as 1%, and searches for glueballs in these decays are highly desirable.

It is shown that in a light-cone representation of nucleons soft-pion theorems which are violated in instant-form quark models can be recovered with suitable choices of parameters of the model. Instantaneous terms must be included for the soft-pion limit. The proton form factors are fit up to $q^2$=3 (GeV/c${)}^2$ in this model.

We show that the QCD van der Waals interaction due to multiple gluon exchange provides a new kind of attractive nuclear force capable of binding heavy quarkonia to nuclei. The parameters of the potential are estimated by identifying multigluon exchange with the Pomeron contributions to elastic meson-nucleon scattering. The gluonic potential is then used to study the properties of cc¯ nuclear-bound states. In particular, we predict bound states of the ${\eta }_c$ with ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ and heavier nuclei. Production modes and rates are also discussed.

We report generating squeezed light via parametric down conversion of a Q-switched and frequency-doubled multi-longitudinal-mode Nd-doped yttrium-aluminum-garnet laser. A local oscillator with appropriate temporal incoherence is needed to homodyne detect the generated squeezed light. As a first approximation, we derive the local-oscillator beam from the same multimode laser whose harmonic is used to pump the parametric down-conversion process. 0.08±0.2 dB of squeezing is routinely observed.

In a crossed-beam experiment the angle-integrated ionization cross section for both positron and electron impact on atomic hydrogen (excluding positronium formation) has been measured in the energy region of 17.5 to 600 eV. Below 450 eV the positron cross section is larger than the electron one, at 50 eV by about a factor of 2. Absolute cross sections are obtained by comparing the electron data with literature values. At energies above 30 eV all theoretical predictions lie below our measured cross sections for positron-impact ionization.

The H mode was achieved in limiter discharges of a tokamak with lower-hybrid current drive for the first time. Simultaneous application of rf powers at two different frequencies such as 1.74 and 2.23 GHz or 1.74 and 2.0 GHz appeared to be effective in the attainment of the H mode. The threshold lower-hybrid power was as low as Ohmic-heating power with hydrogen plasmas. A nearly steady-state edge-localized-mode-free H mode with a duration up to 3.3 sec was established without significant impurity accumulation.

Zero sound attenuation at 8.9 and 26.8 MHz in ${}_{}{}^3{}_{}{}^{}\mathit{B}$ shows an extremum at ${\mathrm{T}}_{\mathrm{AB}}$ in a field of ∼2 kG at low pressures, both in the stationary and in the rotating superfluid. This is in accordance with the prediction that a critical magnetic field separates two types of B phases at the AB transition line, with and without nodes in the energy gap, respectively, and with a change in the nature of the transition. The AB phase transition takes place via an intermediate state, possibly a new phase, characterized by excess sound attenuation.