We study the effect of a lateral superlattice potential on the field-induced spin-density-wave (FISDW) instability of the highly anisotropic two-dimensional electron system under magnetic fields. The superlattice with period double the interchain distance causes an oscillatroy double splitting of the magnetic energy spectrum. It suppresses the transition into the FISDW subphases with even index numbers. We apply this model to the organic superconductor (TMTSF${)}_2$${\mathrm{ClO}}_4$ with the anion-ordering superlattice, and give a possible explanation for its anomalous FISDW behavior.

The magnetic ordering at the surface of epitaxial Cr overlayers on Fe(100) is studied by spin-polarized electron-energy-loss spectroscopy. The exchange asymmetry oscillates with the thickness of the Cr overlayer with a period of about two atomic layers, proving directly that the surface Cr layer has a net ferromagnetic moment and that successive layers order antiferromagnetically. The exchange asymmetry is predominantly due to spin-flip scattering. The spin-flip spectrum broadens toward lower energy with increasing thickness, suggesting that Cr may have a surface-enhanced magnetic moment.

The spin polarization of secondary electrons from a Cr film on Fe(100), measured with scanning electron microscopy with polarization analysis (SEMPA), oscillates as a function of Cr thickness with a period near two atomic layers, consistent with incommensurate spin-density-wave antiferromagnetism in the Cr. The position of a phase slip due to incommensurability varies reversibly by 14 layers over the temperature range of 310 to 550 K. The Cr surface magnetic moment persists well above the Néel temperature of bulk Cr.

We have developed new techniques for measuring infrared spectra at megabar pressures using synchrotron radiation and applied them to study the ${\mathit{Q}}_1$(1), ${\mathit{Q}}_1$(1)+${\mathit{S}}_1$(0), and ${\mathit{Q}}_{\mathit{R}}$(J) vibrational transitions of solid hydrogen to 180 GPa. The frequency difference between the ${\mathit{Q}}_1$(1) infrared and Raman vibrons increases from 3 ${\mathrm{cm}}^{\mathrm{-}1}$ (zero pressure) to 510 ${\mathrm{cm}}^{\mathrm{-}1}$ (180 GPa), including a dramatic increase in intermolecular coupling with pressure. A negative frequency shift is observed for the infrared vibron above 140 GPa. A significant increase in frequency and LO-TO splitting of the lattice phonon is also documented.

Photoluminescence due to radiative transitions between the valence and outermost core bands, in which the Auger process is energetically forbidden, is studied in mixed ${\mathrm{Rb}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Cs}}_{\mathit{x}}$F crystals. The results provide clear evidence that a hole created in the ${\mathrm{Rb}}^{+}$ 4p core band migrates through the crystal, and is trapped at the ${\mathrm{Cs}}^{+}$ 5p core state. The diffusion coefficient of the core holes is estimated to be 1.5×${10}^{\mathrm{-}5}$ ${\mathrm{cm}}^2$/s. Furthermore, a comparison with photoelectron data reveals an important role of relaxation effects in the deexcitation process of core holes.

The energy loss of H projectiles in solid and gaseous Zn has been measured for the first time down to 20 keV/u, showing large differences in the stopping cross section depending on the state of aggregation of the target. For 25-keV protons, the stopping cross section of Zn in the gas phase is found to be 60% higher than that in the solid phase. A charge-state approach to the stopping power of ions in the solid and in the gas is successful in explaining this effect.

For impact of slow multicharged N, Ne, Ar, and I ions on clean polycrystalline gold (impact velocity 1×${10}^4$<${\mathit{v}}_{\mathit{p}}$<15×${10}^4$ m/s, for the first time the statistics of the resulting electron emission have been determined, from which rather precise total electron yields have been derived. From the impact-velocity dependences of yields and the shapes of electron multiplicities two different contributions to electron emission are identified, one probably being due to autonization before surface impact and the other due to faster autoionization just at the surface or already inside the solid.

It is shown that the recent Greenberger-Horne-Zeilinger ‘‘all or nothing’’ contradiction of quantum mechanics with local realism can be exhibited on a macroscopic scale where a large number of particles are incident on each analyzer. We present a formulation of the all or nothing paradox in terms of boson fields, and suggest how the paradox might be realized using a correlated photon triplet. The suggested experiment might be readily extended to test, for the first time to our knowledge, quantum mechanics against local realism for situations of more than one quanta per wave packet incident on each measurement apparatus.

A geometrical phase is constructed for dissipative dynamical systems possessing continuous symmetries. It emerges as the natural analog of the holonomy associated with the adiabatic variation of parameters in quantum-mechanical and classical Hamiltonian systems. In continuous media, the physical manifestation of this phase is a spatial shift of a wave pattern, typically a translation or rotation. An illustration associated with pattern formation in fluids is provided.

We reexamine the stochastic gravitational wave background resulting from inflation and its effect on the cosmic microwave background radiation (CMBR). Measurement by the Cosmic Background Explorer satellite of a CMBR quadrupole anisotropy places an upper limit on the vacuum energy during inflation of ≊5×${10}^{16}$ GeV. Gravitational waves from inflation could produce the entire observed signal if the vacuum energy during inflation was as small as 1.5×${10}^{16}$ GeV at the 95% confidence level. This coincides with recent estimates of grand unification scales inferred from renormalization-group arguments, for Supersymmetric grand unified theories. Further tests of this possibility are examined, based on analyzing the energy density associated with gravitational waves from inflation.

Using the Bethe ansatz equation the mass gap of the chiral SU(n)×SU(n) model is calculated in terms of the Λ parameter in the modified minimal subtraction scheme. The result is in reasonable agreement with recent Monte Carlo data.

Positron asymmetry in the decay of muons produced in ${\mathit{K}}^{+}$→${\mathrm{\mu }}^{+}$ν has been precisely measured in a search for right-handed currents. A novel technique utilizing a ‘‘${\mathit{K}}_{\mathrm{\mu }2}$ muon beam’’ from the at-rest decay of positive kaons in a primary-proton-beam target was employed. A limit of ‖ξ${\mathit{P}}_{\mathrm{\mu }}$‖>0.990 (90% C.L.) was obtained from the energy-integrated positron asymmetry observed in muon spin precession under a transverse magnetic field. This limit sets a new constraint on the mass of a second weak boson (${\mathit{M}}_{\mathit{W}2}$) as well as on the Cabibbo angle of the right-handed sector.

The effects of nucleon-nucleon correlations and color transparency on the final-state interaction of the struck nucleon in electron-nucleus scattering at high-momentum transfer are discussed. The results of realistic microscopic calculations show that both the mechanisms lead to an enhancement of the nuclear transparency, and that the correlation effects are larger up to momenta ${\mathit{Q}}^2$∼4 (GeV/c${)}^2$.

Using a recently developed Boltzmann-Langevin treatment, we study cluster formation in unstable nuclear matter. The self-consistent propagation of the spontaneous fluctuations restores the predictive power of the one-body approach, even when such catastrophic phenomena are addressed.

Charged particles have been observed in collisions of Au on Au at an incident energy of 150A MeV using a high-granularity detector system covering approximately the forward hemisphere in the center-of-mass system. Highly central collisions have been studied using a double selection criterion which combines large charged-particle multiplicities with small transverse-momentum directivities. In this class of events about one quarter of the total nuclear charge emerges as intermediate-mass fragments with nuclear charges Z>2. These fragments are centered at midrapidity and are produced with large transverse velocities.

Since its introduction in 1950, the Feynman-Kac path-integral approach has received limited use in spite of its simplicity in solving the quantum many-body problem. This paper provides a procedure to include permutation symmetries for identical particles in the Feynman-Kac method. It demonstrates that this formulation is ideally suited for massively parallel computers. This new method is used for the first time to calculate energies of the ground state of H, He, Li, Be, and B, and also the first excited state of He.

We report measurements of collisional rate constants for cold Rb atoms held in a magneto-optical trap. ${}_{}{}^{85}{}_{}{}^{}\mathrm{Rb}$ and ${}_{}{}^{87}{}_{}{}^{}\mathrm{Rb}$ display significantly different behavior. At low trap laser intensities, atoms which undergo a hyperfine-changing collision gain sufficient velocity to escape the trap. Since the hyperfine splittings are quite different for the isotopes, the loss rates display a large isotopic dependence in this regime. At higher trap laser intensities, where trap loss is due to inelastic collisions involving excited atoms, a dramatic and unexpected isotopic dependence is seen. Under identical conditions, the loss rate for ${}_{}{}^{85}{}_{}{}^{}\mathrm{Rb}$ is 3.3 times that of ${}_{}{}^{87}{}_{}{}^{}\mathrm{Rb}$.

By using an electron-phonon coincidence method the photon emission asymmetry in the elementary process of bremsstrahlung from transversely polarized electrons was measured for fixed directions of the outgoing electrons and coplanar geometry. For an electron beam of 300 keV incident on a gold target, emission asymmetries up to 35% were found. Even in the case of no deflection of the decelerated outgoing electrons a nonzero photon emission asymmetry was observed. The measurements are a proper test for theories going beyond the first Born approximation.

A novel type of traveling-wave attractor is found in coupled-map lattices. Attractors with different velocities coexist, which are coded by the asymmetry of the wave form. Admissible velocities for the attractors form a series of bands. The velocity is proportional to the winding number of phase slips. If the wavelength and the system size do not match, the wave is modulated by low-dimensional chaos, which leads to spontaneous velocity switching by frustration or reverse transmission of chaotic modulation.

A quasimirrorless laser is shown to exhibit large interferences between macroscopic quantum states when submitted to weak external magnetic fields. Such a device is shown to have potentialities as a high signal-to-noise ratio vectorial magnetometer, especially because of its sensitivity to the mean value of the longitudinal magnetic field and its fast response to magnetic field variations. The behavior of the laser magnetometer is in good agreement with theory.