The time-dependent resistance fluctuations due to motion of H in amorphous PdSi metal films exhibit 1/f noise with two thermally activated peaks, one at 80 K and one shifting with H concentration between 160 and 130 K. The higher peak closely matches an internal-friction peak, showing that the same H hops can relax elastic strain and modulate resistance, while the lower peak reflects hops that do not relax strain. Thus resistance fluctuations and mechanical dissipation provide complementary probes of defect motion.

It is argued that the threshold transition that occurs in the phase-deformation model of charge-density-wave systems in an applied electric field is destroyed in all dimensions by phase slips (amplitude fluctuations). The one-dimensional case is demonstrated using an exactly soluble model.

A theory of optical transitions from a valence state to the conduction band taking into account the dynamical response of the Fermi sea is given using the functional-integral method. The method yields an approximation for the effects of the finite hole mass and finite temperature on the Mahan edge singularities. Magneto-optical spectra are calculated for n-doped quantum wells, which explain the range of observed behavior corresponding to finite-to-infinite hole mass at various temperatures.

A transverse voltage is observed when a current is passed through a narrow channel in a two-dimensional electron gas, using two nonidentical opposite point contacts as voltage probes. The transverse voltage is even in the applied current, and exhibits oscillations as the number of occupied subbands in one of the voltage probes is varied. The effect is shown to be related to the thermopower of a quantum point contact.

Discontinuities have been observed in the energy dependence on magnetic field of the luminescence line corresponding to 2D electron-hole recombination in GaAs/AlGaAs heterojunctions at filling factors ν=2/3, 1/3, 4/5, 3/5, 2/5, 1/5, 1/7, and 1/9. We associate these energy-position shifts with discontinuous behavior of the chemical potential due to condensation of the 2D electrons into an incompressible Fermi-liquid state, and thereby evaluate the energy gaps at fractional filling factors down to 1/9.

Thin gates of type-II superconducting materials have been prepared on top of the two-dimensional electron gas in a GaAs/AlGaAs heterostructure. In an applied magnetic field the flux distribution at the electron gas takes the form of flux tubes which are much narrower than an electron phase coherence length. We observe a qualitatively new weak-localization magnetoconductance for small fields proportional to ‖B‖, in contrast to the ${\mathit{B}}^2$ homogeneous result and in semiquantitative agreement with the theory of Rammer and Shelankov.

Classical theories and their quantum generalizations for the ordered state of a dipole magnet make universal predictions for cubic lattices. In particular, fcc dipolar systems are predicted to be ferromagnets. We present the first direct test of this prediction, in several of the fcc ${\mathrm{Cs}}_2$Na R (${\mathrm{NO}}_2$${)}_6$ rare-earth salts, and find agreement with theory. Predicted quantum anisotropy due to zero-point motion of the spins is not observed.

We present a theory of Raman scattering in the Hubbard model. The scattering of light has two contributions. One gives rise to scattering by spin degrees of freedom in the insulating case where the general form of the scattering Hamiltonian is derived. The fluctuations of the ‘‘chiral’’ spin operator ${\mathrm{\Sigma }}_{{\mathit{S}}_{\mathit{i}}}$⋅(${\mathrm{S}}_{\mathit{i}}$×${\mathrm{S}}_{\mathit{k}}$) are shown to contribute in the ${\mathit{B}}_{2\mathit{g}}$ scattering geometry. The other contributes in the doped case and is shown to probe the fluctuations of the ‘‘stress tensor.’’ This quantity is not conserved, and hence its fluctuations at small q inherent in optical experiments need not be small, in striking contrast to density fluctuations in usual metals.

We diagonalize fully the 4×4 S=1/2 Heisenberg model with nearest-neighbor (${\mathit{J}}_1$) and second-neighbor (${\mathit{J}}_2$) exchanges for several values of ${\mathit{J}}_2$/${\mathit{J}}_1$. For ${\mathit{J}}_2$/${\mathit{J}}_1$≊1/2 the specific heat shows a peak near T=0.27${\mathit{J}}_1$, and the dimer order increases sharply around that temperature. In contrast, the twist order considered earlier by Dagotto and Moreo drops below that temperature, and its T=0 value is roughly the same as that at T=∞. This shows that while the system may develop long-range dimer order (and it certainly has appreciable short-range dimer order) for these values of ${\mathit{J}}_2$/${\mathit{J}}_1$, there is no indication of enhanced twist order.

A field theory for the strong-coupling limit of a one-dimensional copper-oxide model is obtained from a weak-coupling point of view. Complementary aspects of strong correlations and band motion are incorporated in a natural way. Doping induces soliton or antisoliton charge excitations into a state with explicity broken chiral symmetry. The solitons or antisolitons have divergent superconductive pairing-correlation functions and various properties reminiscent of doped holes or electrons in high-temperature superconductors.

Inelastic neutron scattering was used to investigate liquidlike motions and the nature of a dynamic transition in myoglobin, a small globular protein. The signature of the transition is a strong enhancement of low-frequency density fluctuations and a corresponding decrease in elastic scattering above 180 K. It is shown that the line shape of the inelastic-scattering function approximates the scaling behavior predicted for a simple liquid by mode-coupling theories in the vicinity of the liquid-glass transition.

We present a novel cluster algorithm for Monte Carlo simulations of the fully frustrated Ising model on the square lattice. The new method does not suffer from problems of metastability, and is extremely efficient even at T=0. Our algorithm is a special case of a more general Monte Carlo simulation scheme. The general scheme unifies many cluster algorithms that were developed recently in order to accelerate Monte Carlo simulations.

A new approach to clustering based on statistical physics is presented. The problem is formulated as fuzzy clustering and the association probability distribution is obtained by maximizing the entropy at a given average variance. The corresponding Lagrange multiplier is related to the ‘‘temperature’’ and motivates a deterministic annealing process where the free energy is minimized at each temperature. Critical temperatures are derived for phase transitions when existing clusters split. It is a hierarchical clustering estimating the most probable cluster parameters at various average variances.

We study a deterministic version of the cellular automaton first shown to display self-organized criticality. Detailed analysis shows that there exist many coexisting periodic attractors, with a period that is independent of initial condition. This leads us to picture the critical state as the union of many such coexisting, neutrally stable orbits. Dhar’s recently developed formalism [Phys. Rev. Lett. 64, 1613 (1990)] can be used to explain many of the observed regularities.

The mass of bodies with appreciable gravitational self-energy vary in time at a rate proportional to any time variation of the gravitational coupling parameter G. As a result of these mass variations, gravitationally compact bodies will experience anomalous accelerations proportional to their motion relative to the cosmological rest frame in which G=G(t). These effects alter the relationship between the rate of change of orbital period for compact bodies and the rate of change, if any, of G. The binary pulsar system PSR 1913+16 is consequently found to be a somewhat less sensitive probe of a possible nonzero Ġ/G than has been suggested.

We constrain, from the observed properties of diffuse interstellar clouds, the interactions of halo particles with atomic hydrogen.

We show that axions emitted by SN 1987A, with coupling strengths to nucleons in the range 9×${10}^{\mathrm{-}7}$≲${\mathit{g}}_{\mathit{a}\mathit{N}}$≲1×${10}^{\mathrm{-}3}$, would have produced an unacceptably large signal at the Kamiokande proton-decay experiment. Axions with ${10}^{\mathrm{-}10}$≲${\mathit{g}}_{\mathit{a}\mathit{N}}$≲1.4×${10}^{\mathrm{-}6}$ would have altered the neutrino flux from that observed, so using results from SN 1987A alone, one may nominally rule out the entire range ${10}^{\mathrm{-}10}$≲${\mathit{g}}_{\mathit{a}\mathit{N}}$≲${10}^{\mathrm{-}3}$. Uncertainties in our estimates prevent us from categorically excluding a small window around ${\mathit{g}}_{\mathit{a}\mathit{n}}$≃${10}^{\mathrm{-}6}$, which could have interesting consequences for supernova theory and cosmology.

We show that an integral S over the spectral function of spin-1 states of the Higgs sector is constrained by precision weak-interaction measurements. Current data exclude large technicolor models; asymmetry measurements at the CERN ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ collider LEP and the SLAC Linear Collider will soon provide more stringent limits on Higgs-boson strong interactions.

The charged-particle fractional momentum distribution within jets, D(z), has been measured in dijet events from 1.8-TeV p¯p collisions in the Collider Detector at Fermilab. As expected from scale breaking in quantum chromodynamics, the fragmentation function D(z) falls more steeply as dijet invariant mass increases from 60 to 200 GeV/${\mathit{c}}^2$. The average fraction of the jet momentum carried by charged particles is 0.65±0.02(stat)±0.08(syst).

A search has been carried out for long-lived neutral particles which could be created in resonant ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ scattering, with an invariant mass around 1.8 MeV/${\mathit{c}}^2$. A monoenergetic positron beam was scattered from a thin Be foil, and an active-shadow technique was used to suppress elastic ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ scattering. No evidence was found for neutral particles decaying dominantly into ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ pairs, in the lifetime region between 4.5×${10}^{\mathrm{-}13}$ and 7.5×${10}^{\mathrm{-}12}$ s (95% C.L.). This result, together with our previous work, eliminates recent theoretical models that have introduced new neutral particles in this mass region.