Using constant-pressure molecular-dynamics simulation we have studied the nature of ferroelastic phase transition in two-dimensional molecular monolayers. For Lennard-Jones interaction parameters appropriate for ${\mathrm{O}}_2$ molecules, we find, in contrast to the prediction of the renormalization-group calculation of the associated Ginzburg-Landau-Wilson Hamiltonian, a first-order phase transition to the paraelastic phase precipitated by the formation of large density of localized defects of herringbonelike structure.

We calculate the effect of f-wave pairing fluctuations on the collective-mode spectrum of ${}_{}{}^3{}_{}{}^{}\mathit{A}$. Our main result is that the normal flapping mode ceases to be well defined below a temperature ${\mathrm{T}}_{\mathrm{nfl}}$, which is proportional to the (attractive) f-wave coupling constant ${\mathrm{g}}_3$. As one approaches ${\mathrm{T}}_{\mathrm{nfl}}$ from above, the normal-flapping–mode frequency tends rapidly to zero. The corresponding peak feature in the sound attenuation thus provides a sensitive probe of ${\mathrm{g}}_3$.

By application of the perturbed γ-ray distribution method in connection with heavy-ion reactions and recoil-implantation techniques, magnetic single-ion instabilities of Pr, Nd, and Pm ions in small-volume hosts like Ta, W, Os, and Ir have been found. The local susceptibilities observed in the instable Pr, Nd, and Pm systems are strongly reduced compared to both the stable $3^{+}$ and $4^{+}$ ion behaviors. The data indicate a strong 4f–conduction-electron hybridization as the common basic mechanism for the instabilities in Ce, Pr, Nd, and Pm systems.

We observed that the photoemission intensity from solids may depend explicitly on the spin state of the photoexcited electrons. This new phenomenon is explained by spin-dependent transmission through the surface of solids with nonvanishing spin-orbit coupling. It is demonstrated for photoemission from Pt(111) with elliptically polarized synchrotron radiation.

A cluster-model study of Cl and F chemisorbed at a fourfold site of Cu(100) shows that the halogen ionicity is essential -1. The interaction and bonding arise, almost entirely, from the Coulomb attraction between the charged halogen and metal and from the polarization of the electrons associated with these units; covalent bonding makes a very small contribution. The polarization dramatically reduces the dipole moment from that given by the unpolarized ionic units. Thus, changes in the work function are not a measure of the adsorbate ionicity.

We investigate the physical processes which determine the optical spectra of modulation-doped semiconductor quantum-well structures as a function of doping. We argue that even at low doping concentrations, excitons are heavily dressed by charge- and spin-density excitations of the Fermi sea, implying, already in that limit, a Stokes shift between emission and absorption. For all doping concentrations, the charge and spin polarization of the Fermi sea due to many-body effects leads to an enhancement of the symmetry breaking in quantum-well structures, which may explain polarization anomalies observed in luminescence.

A strong temperature and magnetic field dependence of conductivity has been found in ${\mathrm{Cd}}_{0.95}$${\mathrm{Mn}}_{0.05}$Se. The effect appears to result from the influence of magnetic polarons and of the exchange-induced spin splitting on the quantum corrections to the conductivity of disordered magnetic metals.

Narrow Xe 5p→6s and Kr 4p→5s resonances (ΔE<80 meV) have been observed in the adsorbate phase on Pt(111) and graphite (0001). The photon-induced transitions reveal an additional level splitting compared to the gas phase and the intensities show a significant substrate dependence. The resonances were detected via spectroscopy of the electrons emitted due to a subsequent relaxation decay of the excited state. Measurement of the electron-spin polarization clarified the nature of the new decay mechanism observed and furthermore provided an unambiguous quantum-number labeling of the resonances.

The nonlinear response of cooled extrinsic Ge photoconductors to periodic excitation is experimentally studied. Measured phase portraits, Poincaré sections, and power spectra show subharmonic behavior characteristic of driven nonlinear oscillators including a period-doubling cascade to chaotic oscillation which produces excess broad-band noise with observed noise temperatures as high as ∼${10}^9$ K. The experimental results are in qualitative agreement with numerical simulations of a simple rate-equation model of extrinsic photoconductors.

Deposition of arsenic on Si(100) results in a well-ordered, highly passivated, and stable surface. From a comparison between angle-resolved photoemission data and ab initio pseudopotential calculations we conclude that the observed 2×1 reconstruction is caused by the formation of symmetric As-As dimers on the surface. The calculated surface band dispersion for this model is in excellent agreement with experiment.

We present trajectory calculations of electron- or photon-stimulated desorption of positive ions from alkali halides via the ‘‘Coulomb explosion’’ mechanism, in which desorption is due to the repulsive forces resulting from formation of a positive halogen ion (${\mathrm{F}}^{+}$). In many circumstances, the lattice is shown to rearrange within ∼${10}^{\mathrm{-}13}$ s and trap the ${\mathrm{F}}^{+}$ ion, thus blocking desorption. The dynamic lattice distortions are crucial in the determination of which desorption channels are open, which species desorb, and what final kinetic energies are obtained.

The first electronic structure calculation of the ordered α, β, and γ cubic phases of an ‘‘interstitially filled tetrahedral compound’’ ${\mathrm{A}}^{\mathrm{I}{\mathrm{B}}^{\mathrm{II}{\mathrm{C}}^{\mathrm{V}}}}$ (where the ${\mathrm{B}}^{\mathrm{II}}$ and ${\mathrm{C}}^{\mathrm{V}}$ atoms occupy the normal zincblende sites and ${\mathrm{A}}^{\mathrm{I}}$ occupies one of the empty zincblende tetrahedral interstitial sites) reveals strongly covalent (${\mathrm{B}}^{\mathrm{II}\mathit{-}{\mathrm{C}}^{\mathrm{V}}}$) and strongly ionic (${\mathrm{A}}^{\mathrm{I}\mathit{-}{\mathrm{C}}^{\mathrm{V}}}$) bonds in the same structure, uperior cohesion relative to the III-V analog (GaAs), and semiconducting (α and β forms) as well as metallic (γ-form) behavior.

We report the first systematic study of the corrections to the electron density of states of a 1D system, ultranarrow granular aluminum wires. These corrections do not have the ${\mathrm{V}}^{\mathrm{-}1/2}$ dependence predicted by theory, but are significantly larger than the corrections observed in corresponding bulk samples. At high magnetic fields, low temperatures, and very low voltages, we see evidence of a logarithmic gap in the density of states.

We discuss the conditions that dynamic symmetries impose on the scattering S matrices and construct these matrices for problems with SO(2,1), SO(2,2), and SO(2,3) dynamical groups. The latter group appears to be very useful for the analysis of heavy-ion collisions.

The route to chaos found from the delay-differential rate equations is basically different from the subharmonic cascade which is generic of the adiabatic-following-approximation equation. The Lyapunov dimension of each chaotic attractor is found to increase linearly with γ${\mathrm{\tau }}_{\mathrm{R}}$, the ratio of the delay time to the medium lifetime. This clearly shows the invalidity of the difference-equation mapping whose dimension never exceeds 2.

We describe a new method of measuring the Lense-Thirring relativistic nodal drag using LAGEOS together with another high-altitude, laser-ranged, similar satellite with appropriately chosen orbital parameters. We propose, for this purpose, that a future satellite such as LAGEOS II have an inclination supplementary to that of LAGEOS. The experiment proposed here would provide a method for experimental verification of the general relativistic formulation of Mach’s principle and measurement of the gravitomagnetic field.

We used the relativistic Doppler effect to shift the energy of the fourth-harmonic photons of a Nd-doped yttrium aluminum garnet laser into the range from 1.4 to 15.8 eV in a moving atom’s reference frame by varying the angle of intersection theta between the laser beam and an 800-MeV atomic hydrogen (${\mathrm{H}}^0$) beam. We measured the intersection angle theta for several well known Lyman transitions (1s to np) in ${\mathrm{H}}^0$ and fitted these data by the form E=($E_0$/$g_0$)γ(1+β costheta). The value of $E_0$/$g_0$ obtained in this manner, compared with the measured value of $E_0$ for the laser photons, yielded $g_0$=1.000 04(27) at β≃0.84. The prediction of special relativity that $g_0$=1 is thus verified to an accuracy of 2.7×${10}^4$.

A two-level system is treated which interacts with a degenerate fermionic heat bath. Arbitrarily strong screening by fermions is taken into account. The hopping of the two-level system may be spontaneous or assisted by the fermionic bath. By derivation of scaling equations it is shown for the spin-(1/2) case that because of the assisted hops the two-level system cannot be localized in one of the states.

We consider the problem of a free particle in a rigid box with one wall fixed and the other oscillating periodically in time. The spectral properties of the evolution operator are calculated. We find that by a tuning of Planck’s constant, the statistics of the quasienergy spectrum go continuously from showing Poisson to Gaussian-orthogonal-ensemble-like properties. This change is related to a transition from localized to extended states in energy space. We make the conjecture that recent results of microwave excitations on quasi one-dimensional highly excited hydrogen atoms may be related to this work.

Consequences of geometrical constraints from integrability along all super lightlike lines are examined in N-extended supergravity theories. It is shown that these constraints give rise, through Bianchi identities, to equations of motion of the conformal type for all forms of physical fields, with N>4. Our results point to an integrability program for N>4 supergravity similar to that for N>2 supersymmetric Yang-Mills fields.