We present the first measurements at millikelvin temperatures of both the real and the imaginary parts of the transverse-acoustic impedance of an oscillating surface in contact with dilute solutions of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ in ${}_{}{}^4{}_{}{}^{}\mathrm{He}$, as well as with pure ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ with and without a surface boundary layer of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$. Except for pure ${}_{}{}^3{}_{}{}^{}\mathrm{He}$, large departures from hydrodynamic behavior are found which are inconsistent with slip theories incorporating specular scattering at the boundary. The effects of the ${}_{}{}^4{}_{}{}^{}\mathrm{rich}$ surface boundary layer and of surface roughness are discussed.

A heavy particle moving by hopping on a lattice is considered. The screening and assisted hopping due to the electrons result in logarithmic contributions to the scattering amplitude. In the study of a one-dimensional model, scaling similar to the anisotropic antiferromagnetic Kondo problem is found. The large-scaled couplings reduce the width of the heavy particle band essentially. The results obtained hold also for heavy particles forming a degenerate Fermi gas.

Microcrystalline samples of BC8 silicon III and hexagonal silicon IV, grown under high pressure in the diamond anvil cell, remain metastable at ambient pressure. Hall-effect and low-temperature resistivity measurements show Si III to be a hole semimetal with p≊5×${10}^{20}$ ${\mathrm{cm}}^{\mathrm{-}3}$. Photoconductivity data show that Si IV, like Si I, is an intermediate-gap semiconductor. The observed behavior confirms theoretical predictions on these two new elemental materials.

We study the heat diffusion and the thermal conductivity of the interacting disordered electron liquid in the metallic regime close to the metal-insulator transition. The heat-diffusion constant provides a direct measurement of the quasiparticle diffusion constant which scales differently from the charge-diffusion coefficient. The thermal conductivity scales like the electrical conductivity establishing the validity of the Wiedemann-Franz law up to the metal-insulator transition.

The linearity of the power response of yttrium iron garnet films to a microwave pulse having length shorter than the delay time characteristic of the specimen is investigated. In particular, a threshold is found above which output power increases with respect to standard linear trend. The above novel effect, analyzed in some detail on five epilayers of different thicknesses, cannot be explained in terms of usual nonlinear processes. An interpretation in terms of soliton excitation, accounting for the existence in the system of both intrinsic nonlinearity and dispersion, is proposed.

The effective screened interaction for electrons in a layered electron gas is derived. This interaction reflects the existence of the plasmon band. This unique structure of collective excitations, absent in both the three-dimensional and the two-dimensional electron gas, affects electronic properties of the layered electron gas. With use of the dynamical random-phase approximation the quasiparticle self-energy, effective mass on the Fermi surface, and lifetime are calculated as functions of electron density and distance between layers. The lifetime exhibits a dramatic dependence on dimensionality and layering of the electron gas.

We have measured current-voltage characteristics of very small [0.4–0.02 (μm${)}^2$] Sn-${\mathrm{SnO}}_{\mathrm{x}}$-Sn tunnel junctions, having estimated charging energy $e^2$/2C comparable to their other characteristic energies. In the higher-$R_n$ devices, after rising just below $T_c$, $I_c$ decreases as the temperature is decreased further, and then increases again, at the lowest temperatures. Although the junctions are hysteretic, a significant resistance is found at currents below $I_c$. We suggest an interpretation involving the quantum nature of φ and the competition between the charging, Josephson, and thermal energies of the system.

The 5f spectral weights in the heavy-fermion alloy system ${\mathrm{U}}_{\mathrm{x}}$${\mathrm{Y}}_{1\mathrm{-}\mathrm{x}}$${\mathrm{Al}}_2$ (x=0.1,0.02) have been measured by resonant photoemission. The major features of the spectra of the dilute systems are identical to those for x=1, showing that single-site effects dominate the large–energy-scale features of the spectrum even in the concentrated system.

We calculate the Hohenberg-Kohn-Sham energy response kernel $K_{\mathrm{xc}\left(\mathrm{q}\right)}$ exactly for the high-density electron gas, and thus generalize the classic work of Ma and Brueckner to finite wave vector. The results are relevant to (1) density-functional theory, where we verify that one of the key assumptions used in the Langreth-Mehl functional was qualitatively correct and suggest possible improvements; (2) dielectric response theory, where we exactly calculate the leading correction to the static Lindhard screening function; and (3) a static attractive 1/$r^6$-like interaction between like-charged point particles—we verify the recent suggestion of Maggs and Ashcroft that such an interaction exists and calculate its value.

We report experimental values for the band-edge hydrostatic deformation potentials of GaAs and InP semiconductors. The deformation potentials are determined directly by observation of the universal pressure derivative of transition-metal defect levels and consideration of this pressure derivative in the context of recent models of heterojunction band lineup. We obtain values of -9.3 and -7.0 eV for the conduction-band deformation potentials of GaAs and InP, respectively, determined from the uniaxial-stress deep-level transient spectroscopy on defect levels of Ti and V.

The electron-stimulated ${\mathrm{O}}^{\mathrm{-}}$ desorption yields from ${\mathrm{O}}_2$ condensed on a thick rare-gas (Ar, Kr, or Xe) film are reported. It is shown that coherent scattering of electrons in the rare-gas film dramatically enhances the ${\mathrm{O}}^{\mathrm{-}}$ yields near the Bragg reflection energies.

Multiple-quantum NMR coherences created from the coherent excitation of the soliton nuclear hyperfine interactions are generated and detected by electron-spin echoes in polyacetylene, (CH${)}_{\mathrm{x}}$. The multiple-quantum spectra observed for both trans- and cis-(CH${)}_{\mathrm{x}}$ are identical from 4 to 300 K, establishing that both the soliton spin-density distribution and on-chain mobility are identical in these isomers throughout this temperature range.

Recently, Berry recognized that topological phase factors may arise when a quantum mechanical system is adiabatically transported around a closed circuit. We have measured Berry’s topological phases by polarized-neutron spin rotation in a helical magnetic field. Berry’s law is thus verified for fermions.

It is pointed out that for the pulsed rotators the classical resonance-overlapping criterion for the onset of chaotic motion implies the existence of avoided crossings among an arbitrarily large number of quantum levels at the classical limit ħ small, nħ=A close to a classical resonance.

The spectrum of excitations of a spin-(1/2 Heisenberg chain in the region of anisotropy 1>Δ>0 (where the model is critical and has no bound states) exhibits a ‘‘tower structure’’ in the energy-momentum plane as predicted by the hypothesis of conformal invariance. For a given magnetization the apices of the towers are located on a parabola. The spectrum shows remarkable degeneracies at some discrete values of Δ given by the Tutte-Behara numbers.

We develop a two-potential approach to the decay of a quasistationary state. The method enables us to obtain a simple algebraic formula for the decay width and the energy shift of a metastable state. The quasiclassical limit of the width found leads to the well-known Gamow formula, this time with a well-defiend preexponential factor. The energy shift together with its quasiclassical limit is obtained in closed form.

Positrons from a ${}_{}{}^{27}{}_{}{}^{}\mathrm{Si}$ source, obtained through the reaction ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$(p,n${)\mathrm{}}^{27}$Si, were scattered off electrons in a target of polyethylene, and $e^{+}$$e^{\mathrm{-}}$ coincidences were detected in a pair of plastic scintillators. The detector aperatures were restricted to accept only events corresponding to maximum momentum transfer at center-of-mass angle π/2. The variation with energy of the corresponding laboratory angle was utilized to obtain the scattering excitation function from the continuous positron spectrum. Center-of-mass kinetic energies in the $e^{+}$$e^{\mathrm{-}}$ system covered the range 342 to 845 keV.

The nucleus ${}_{}{}^{152}{}_{}{}^{}\mathrm{Dy}$, with sharp ridges in the γ-γ energy correlation matrix, stands out from three neighboring nuclei which exhibit less pronounced structures. The ridges include the observed discrete superdeformed band, but must be composed mainly of unresolved superdeformed bands, which decay predominantly to less deformed states. A simple decay model is proposed.

Above-threshold multiphoton ionization angular distributions have been studied for elliptical laser polarization in xenon and krypton. In contrast to previous linear and circular polarization studies, the angular distributions are strongly dependent on the order of the above-threshold-ionization peak, even for very high-energy electrons. This provides a new test for theories of atomic photoionization in intense laser fields. A standard nonperturbative model, when generalized to accommodate elliptical polarization, is found to yield angular distributions which are in reasonable accord with experimental results.

An improvement in precision beyond the limit set by the vacuum-state or zero-point fluctuations of the electromagnetic field is reported for the measurement of phase modulation in an optical interferometer. The experiment makes use of squeezed light to reduce the level of fluctuations below the shot-noise limit. An increase in the signal-to-noise ratio of 3.0 dB relative to the shot-noise limit is demonstrated, with the improvement currently limited by losses in propagation and detection and not by the degree of available squeezing.