We use the Hartree-Fock approximation to investigate the ground state of a system consisting of spatially separated electron and hole layers in strong magnetic fields. When the layer separation is larger than a critical value a novel excitonic-density-wave state is found to have a lower energy than either a homogeneous exciton fluid or a double charge-density-wave state. The order parameters of the state satisfy a sum rule similar to that of a charge-density-wave state in a two-dimensional electron system. A possible connection between the new state and a recent experimental result is discussed.

We study the criticality at the spin-glass-ferromagnetic-paramagnetic multicritical point in the d=3, ±J distribution, random-bond Ising model. Using high-temperature expansions to order ${\mathit{T}}^{\mathrm{-}34}$, we estimate that the multicritical point N lies on the Nishimori line at ${\mathit{T}}_{\mathit{c}}$/J=1.690±0.016. Along this line the critical exponents are found to be γ=1.80±0.15 and ν=0.85±0.08. The latter is clearly consistent with the rigorous exponent inequality ν≥2/d. We also calculate the crossover exponent φ and show that the scaling axes at N are in agreement with the recent predictions of Le Doussal and Harris.

Oscillations with a period of two Cr monolayers were measured in the antiferromagnetic exchange coupling between Fe magnetizations separated by Cr. The coupling was measured on a sample consisting of a Au(20 Å)/Fe(50 Å)/Cr(0–18 Å wedge) film deposited by molecular-beam epitaxy on a Fe[100] single-crystal ‘‘whisker.’’ The Cr and Fe grew monolayer by monolayer as monitored by reflection high-energy-electron diffraction. The coupling was determined from the magneto-optic Kerr effect. It was antiferromagnetic for 5–18 Å Cr with four strong peaks and a maximum value of -0.60 mJ/${\mathrm{m}}^2$ for eight monolayers of Cr.

Through Monte Carlo simulations we have studied the spin-glass susceptibility of two-, three-, and four-dimensional spin glasses in a magnetic field. We find that in four dimensions curves of constant susceptibility curve upward as the temperature is lowered, in a manner indicative of the presence of a de Almeida–Thouless (AT) line of phase transitions. In three dimensions the curves of constant susceptibility also appear to curve up, although not as sharply. In contrast, in two dimensions we do not see indications of an AT line.

Some generic properties of charged instanton gases are established in arbitrary dimension, including the fact that the self-energy, if it diverges, must diverge as the logarithm of the correlation length. A real-space renormalization is carried out in d=3 and recursion relations obtained under the assumption that the model can disorder without instantons. They reveal that for models with nontrivial Haldane phases, the correlation-length exponent is not altered by hedgehogs, and that generic instanton gases undergo first-order transitions in three dimensions. In special cases a second-order transition with continuously varying exponents is found.

An exact solution describing flux creep in high-${\mathit{T}}_{\mathit{c}}$ superconductors is found, assuming the creep activation barrier U grows logarithmically with decreasing current j: U=${\mathit{U}}_0$ ln(${\mathit{j}}_0$/j). For incomplete flux penetration, the flux density B is a function of the single variable ξ=x/${\mathit{t}}^{1/(\mathrm{\sigma }+2)}$, σ=${\mathit{U}}_0$/T, and the system considered exhibits self-organized criticality. In a fully penetrated sample, B depends separately upon x and t. A sharp transition between these regimes occurs when the flux fronts from opposite sides of the sample meet, resulting in a kink in the magnetization relaxation curve.

We study the response of pinned flux lattices, under small perturbations in the driving force, below and close to the pinning-depinning transition. For driving Lorentz forces below $F_c$ (the depinning force at which the whole flux lattice slides), the system has instabilities against small force increases, with a power-law distribution characteristic of self-organized criticality. Specifically, $D\left(d\right)\mathrm{}\sim d^{-1.3\mathrm{}}$, where $d$ is the displacement of a flux line after a very small force increase. We also study the initial stages of the motion of the lattice once the driving force overcomes the pinning forces.

Upon cooling partially polymerized vesicles are observed to undergo a spontaneous transition to a wrinkled rigid structure. The transition is reversible: The vesicles unwrinkle upon heating. A model is presented suggesting that this transition could be the membrane equivalent of a glass transition.

The vibrational modes of hydrogen embedded in a Ni crystal are shown to be detectable by high-resolution electron-energy-loss spectroscopy and to be unambiguously distinguishable from the vibrational modes of adsorbed hydrogen on the basis of the dependence of the inelastic electron intensity on electron impact energy. The embedded hydrogen has a vibrational frequency of 800–850 ${\mathrm{cm}}^{\mathrm{-}1}$ and is observed to recombine and desorb as ${\mathrm{H}}_2$ between 180 and 220 K. The absorption of hydrogen into Ni(111) is achieved under UHV conditions by exposure to atomic hydrogen. As much as an equivalent of 8 monolayers has been absorbed.

Practical application of the generalized Bell’s theorem in the so-called key distribution process in cryptography is reported. The proposed scheme is based on the Bohm’s version of the Einstein-Podolsky-Rosen gedanken experiment and Bell’s theorem is used to test for eavesdropping.

Chaos introduces essential complications into semiclassical mechanics and the conventional wisdom maintains that the semiclassical time-dependent Green’s function fails to describe the quantum dynamics once the underlying chaos has had time to develop much finer structure than a quantum cell (h). We develop a method to evaluate the semiclassical approximation and test it for the first time under these circumstances. The comparison of the quantum and semiclassical dynamics of the stadium billiard shows remarkable agreement despite the very intricate underlying classical dynamics.

We evaluate the magnetic moment μ=geħ/2${\mathit{m}}_{\mathrm{\tau }}$c of the τ lepton. This is interesting from a purely theoretical point of view, although an experimental measurement, though difficult, may be possible in the future. Our result, including strong- and weak-interaction contributions, which are large, is ${\mathit{a}}_{\mathrm{\tau }}$=(g-2)/2=11 773(3)×${10}^{\mathrm{-}7}$.

Multifragment events for intermediate-mass fragments (3≤Z≤12) with multiplicity up to four have been observed in the reaction of 0.90 and 3.6 GeV ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ ions with ${}_{}{}^{\mathrm{natAg}}{}_{}{}^{}$ nuclei. Fragment energy spectra and angular distributions are found to be dependent on event multiplicity. The data suggest significant modification of the Coulomb field of the emitting source.

The dynamics of electronic autoionization in ${\mathrm{O}}_2$ has been studied using a new apparatus which combines a free-jet supersonic expansion with synchrotron radiation. Ions and electrons were analyzed by a double time-of-flight spectrometer. The spin-orbit sublevels of the ${}_{}{}^3{}_{}{}^{}\mathrm{\Pi }_{\mathrm{u}}^{}{}_{}{}^{}$ (v=0 and 2) Rydberg states in ${\mathrm{O}}_2$ were selectively excited and the resulting ${\mathrm{O}}_2^{+}$ final states were determined by time-of-flight photoelectron spectros copy. A strong variation of the ${}_{}{}^2{}_{}{}^{}\mathrm{\Pi }_{1/2\mathrm{}\mathit{g}}^{}{}_{}{}^{}$${:}^2$${\mathrm{\Pi }}_{3/2\mathrm{}\mathit{g}}$ branching ratio was observed. This variation results from the selection of a single continuum wave function in the autoionization process.

We report the first observation of quantum beats in the resonance fluorescence of a bound exciton in a semiconductor, the ionized-donor exciton complex in CdS. Measurements of the polarization behavior and magnetic-field dependence of the beats permitted a detailed investigation of strain effects and magneto-optical parameters of the states. From the damping of the beats, coherence times of the order of several hundreds of picoseconds are deduced. For the neutral-donor and -acceptor bound exciton states, very rapid dephasing with coherence times of the order of 20 ps is found.

We have demonstrated experimentally that the contrast lost, due to placing slabs of a material having a neutron optical potential in one leg of a neutron interferometer, can be restored by spectral filtering of the beams leaving the interferometer immediately before detection. The non-Gaussian spectral distribution of the neutrons traversing the interferometer in our experiment leads to an unexpected phase reversal of the interferograms.

It is shown that the frequency-temperature spectrum recently observed by Wu et al. in developed convective turbulence, ${\mathit{F}}_{\mathit{T}\mathit{T}}$(ω)∝${\mathrm{\omega }}^{\mathrm{-}1.4}$, follows from the condition that the entropy flux in $ k — space is constant, just as the Kolmogorov-Obukhov spectrum of barotropic turbulence, ${\mathit{F}}_{\mathit{V}\mathit{V}}$(k)≃(ɛ/ρ${)}^{2/3}$${\mathit{k}}^{\mathrm{-}11/3}$, follows from the condition kinetic-energy flux ɛ(k)=ɛ. On the contrary, for convective turbulence ɛ(k) changes as ${\mathit{k}}^{\mathrm{-}4/5}$ because of conversion of kinetic energy into a potential energy, which leads to a stronger k dependence of the double velocity moment [${\mathit{F}}_{\mathit{V}\mathit{V}}$(k)∝${\mathit{k}}^{\mathrm{-}21/5}$] than that for barotropic turbulence.

We present results of the first orientation-dependent study of the spin dynamics of the low-field spin-ordered phase of solid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$, the U2D2 phase. The results of a hydrodynamical treatment of the spin dynamics describe the observed behavior exceedingly well; however, only if a field- and orientation-independent negative shift, not provided by the theory, is properly incorporated into the equations. This shift does not arise from a lattice distortion as had been expected, and its measured temperature dependence suggests an unknown nonhydrodynamical origin.

We determined the superfluid density ${\mathrm{\rho }}_{\mathit{s}}$ from the speed of heat pulses, using a hydrodynamic model that contains coupling between the aerogel and the helium. To investigate the universality of the exponent of ${\mathrm{\rho }}_{\mathit{s}}$, measurements of ${\mathrm{\rho }}_{\mathit{s}}$ were taken from saturated vapor pressure to 29 bars. Fitting ${\mathrm{\rho }}_{\mathit{s}}$ with a pure power law in reduced temperature leads to a pressure-dependent exponent. Inclusion of a confluent singular term in the fits reveals a pressure-independent exponent ζ=0.755±0.003 which differs from ζ=0.672 for bulk helium.

A mechanical degenerate parametric amplifier has been devised which greatly increases the motional response of a microcantilever for small harmonic force excitations. The amplifier can improve force detection sensitivity for measurements dominated by sensor noise or backaction effects and can also produce mechanical squeezed states. In an initial squeezing demonstration, the thermal noise (Brownian motion) of the cantilever was reduced in one phase by 4.9 dB.