A quasi-one-dimensional S=1 antiferromagnet with XXZ-type intrachain couplings and Ising-type interchain couplings is studied. It has been suggested that when the interchain couplings are sufficiently small such a system has no long-range order, even at T=0, because of strong quantum fluctuation caused by the Haldane gap. Treating the problem in a restricted Hilbert space which describes the low-energy behavior of S=1 antiferromagnets rather accurately, we prove two theorems which establish the existence of a unique disordered ground state with a gap.

The interactions in the magnetoplumbite isomorph ${\mathrm{SrCr}}_8$${\mathrm{Ga}}_4$${\mathrm{O}}_{19}$ are highly frustrated. Thermodynamic data are presented and show the existence of a transition from paramagnetic to spin-glass ordering but only at ${\mathit{T}}_{\mathit{c}}$=3.3 K, despite the high Curie-Weiss temperature of 515 K. Other unusual properties include a low-temperature specific heat varying as ${\mathit{T}}^2$ and an inverse relationship of ${\mathit{T}}_{\mathit{c}}$ to magnetic-ion concentration for a set of differently prepared crystals. This result is conjectured to arise from competition between 2D frustration and a tendency toward 3D order, controlled by preferential site substitution.

We have measured the low-temperature magnetization response of ${10}^7$ isolated mesoscopic copper rings to a slowly varying magnetic flux. At sufficiently low temperature, the total magnetization response oscillates as a function of the enclosed magnetic flux on the scale of half of a flux quantum. The amplitude of the oscillatory moment is ≊1.2×${10}^{\mathrm{-}15}$ ${\mathrm{Am}}^2$ and decreases exponentially with increasing temperature on the scale of the correlation energy ${\mathit{E}}_{\mathit{c}}$=hD/(2L${)}^2$≊80 mK. This is evidence for a flux-periodic persistent current in each ring of average value 3×${10}^{\mathrm{-}3}$e${\nu }_{\mathit{F}}$/L.

The Peierls instability for linear spectrum fermions is considered. It is shown that for a sufficiently strong fermion interaction a phase transition takes place, and the fermions become massive. This phenomenon is analogous to chiral symmetry breaking in 3+1 QED. The large-N approximation is applied. It is shown that in the weak-coupling limit fluctuations of the order parameter are strong and can lead to a first-order phase transition. In the strong-coupling limit, the phase transition is of the second type. The effect of anisotropy of the spectrum is discussed.

Several recent models of high-${\mathit{T}}_{\mathit{c}}$ superconductivity predict static internal magnetic fields along the c axis due to spontaneously broken parity and time-reversal symmetries. Muon spin relaxation has been used to study the internal fields in c-axis-oriented samples of sintered ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ and of thick-film ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_8$. The magnitude, anisotropy, and temperature dependence of the observed fields favor a nuclear dipolar origin. Any anomalous fields at ${\mathrm{\mu }}^{+}$ sites in bulk ${\mathrm{CuO}}_2$ superconductors must be ≲0.08 mT.

The lifetime of the first excited level of the symmetric C-H stretching mode of ${\mathrm{CH}}_3$S chemisorbed on a Ag(111) surface was measured by picosecond vibrational spectroscopy. A biexponential decay (∼3- and 63-ps lifetimes at 300 K) was observed, with a substantial temperature dependence of the slow component. Both decay processes are assigned to intramolecular vibrational relaxation. The decay rates are 2 orders of magnitude too fast to be explained by electron-hole-pair damping by the metal substrate.

A picosecond time-resolved infrared technique has been used to measure the transient response of vibrationally excited CO adsorbed on the surface of a Pt(111) single crystal. Transient bleaching signal decay is interpreted as giving ${\mathit{T}}_1$ for damping of vibrationally excited CO. Transient absorption is discussed in terms of transitions from the excited adsorbate band to overtone levels.

Sensitive micropipet methods have been used to measure the relation between tension and the projected surface area in fluid membranes of vesicles over a 4-order-of-magnitude range in tension (${10}^{\mathrm{-}3}$–10 dyn/cm). In the low-tension regime (<0.5 dyn/cm), the data confirm the prediction of equilibrium theory that the projected area should increase logarithmically with tension as shape fluctuations become progressively restricted. The slope of log(tension) versus area dilation yields and the elastic bending modulus of the membrane. In the high-tension regime, the projected area crosses over to vary linearly with tension due to direct expansion of area per molecule.

It is shown on the basis of numerical data that the normalized localization length of eigenvectors of band random matrices follows a scaling law. The scaling parameter is ${\mathit{b}}^2$/N, where b measures the bandwidth and N is the size of the matrix.

We present a solvable singular quantum billiard which displays fully developed wave chaos. Its level statistics is investigated and proved to coincide with predictions of the Gaussian orthogonal ensemble of random matrices. The corresponding wave functions are shown to be well approximated by a Gaussian ransom variable.

We investigate the order-parameter distribution P(q) of the Ising spin glass with nearest-neighbor interactions in four dimensions using Monte Carlo simulations on lattices of linear dimension up to L=6. We find that, below the transition temperature ${\mathit{T}}_{\mathit{c}}$, the weight at small q seems to saturate to a nonzero value as the size increases, similar to the infinite-range Sherrington-Kirkpatrick model. We discuss our results in the light of recent theoretical predictions for the nature of the spin-glass phase.

We show that for fermions interacting with potentials with a momentum cutoff the Hamiltonian is stable and defines a time evolution in the Heisenberg representation. A mixing property of these systems is derived.

In calculating the transport properties of relativistic electromagnetic or quark-gluon plasmas microscopically, one encounters the problem of divergent constituent cross sections arising from the exchange of transverse photons or gluons. Inclusion of Landau damping of the virtual quanta exchanged provides an effective long-wavelength cutoff. Dominance of Landau damping over a possible magnetic mass in QCD is demonstrated in the weak-coupling limit. The viscosities of a pure gluon plasma and a quark-gluon plasma are calculated in weak coupling from a variational solution to the Boltzmann equation.

The neutrino-induced nuclear transition ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(${\nu }_{\mathit{e}}$,${\mathit{e}}^{\mathrm{-}}$${)}^{12}$N (g.s.) has been observed with a 15-ton fine-grained tracking detector. The exclusive final state is identified by both an electron track and the positron decay of the ${}_{}{}^{12}{}_{}{}^{}\mathrm{N}$. From the observation of 181±17 ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(${\nu }_{\mathit{e}}$,${\mathit{e}}^{\mathrm{-}}$${)}^{12}$N (g.s.) events with subsequent positron decays the flux-averaged cross section, equivalent to the cross section for 35.0-MeV neutrinos, is [1.05±0.10(stat)±0.10(syst)]×${10}^{\mathrm{-}41}$ ${\mathrm{cm}}^2$. This result is in good agreement with recent calculations.

We solve a set of Faddeev equations for some realistic two-nucleon potentials, taking into account the two-pion-exchange three-nucleon interaction, the Coulomb interaction, and the charge-independence- and charge-symmetry-breaking (CIB and CSB) interactions. After 32 case studies, we find a very good linear relationship between ${}_{}{}^3{}_{}{}^{}\mathrm{H}$ and ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ binding energies, from which we deduce a model-independent value for the Coulomb energy difference (648±4 keV for the finite-size protons) and the CIB and CSB nuclear effects. With other small effects, these effects reasonably account for the ${}_{}{}^3{}_{}{}^{}\mathrm{-}_{}^3{}_{}{}^{}$he binding-energy difference.

We excited helium atoms using 10–20-keV ${\mathrm{H}}_2^{+}$ (${\mathrm{D}}_2^{+}$) ion impact and investigated the intensity of the λ($4^3$D-$2^3$P)=447 nm line as a function of an electric field -2 kV/cm≲F≤+2 kV/cm applied antiparallel and parallel to the ion beam. The recorded signals were strongly asymmetric with respect to the sign of the electric field. This asymmetry is explained by assuming a coherent excitation of He levels with different angular momenta (4d,4f and 5f,5g). These measurements demonstrate that angular momentum coherences of impact-excited states can also be observed in nonhydrogenic systems.

We report a new kind of multiphoton dissociation in intense laser fields. ${\mathrm{H}}_2^{+}$ molecular ions were formed in above-threshold ionization of ${\mathrm{H}}_2$ gas by intense 532-nm, 100-ps laser pulses. Observations suggest that multiphoton couplings soften the molecular bond, resulting in dissociation at laser intensities over 50 TW/${\mathrm{cm}}^2$. The ion-dissociation spectra have multiple peaks caused by multiphoton transitions during dissociation of ${\mathrm{H}}_2^{+}$.

The transfer of negative pions in mixtures of bromodecane and carbon tetrachloride has been investigated by combined measurements of ${\mathrm{\pi }}^0$’s produced from nuclear capture on hydrogen and pionic x rays following Coulomb capture on bromine and chlorine. A significant fraction of pion transfer occurs via an external transfer process. The results represent the first direct observation of transfer in condensed matter.

Self-consistent calculations of radio-frequency (rf), current-drive requirements are presented for tokamak, magnetohydrodynamics equilibria which have been tested for stability. These stable equilibria include ones which have been chosen to have a large fraction of the current generated by the neoclassical bootstrap effect, greatly reducing the required current-drive power.

In a circular cross-section plasma bounded by a limiter, the H-mode transition is triggered by a rapid rampdown in plasma current during auxiliary heating, even in the case when the edge electron temperature gradually decreases prior to the transition. This result suggests that the transition is governed by the enhancement of the magnetic shear near the plasma edge, associated with the radial modification of the edge current-density profile.