A novel method is presented to study the dynamics of vortices in superconducting films at fields close to the upper critical magnetic field. It is shown that moving flux lines in the gate of a superconductor-oxide-semiconductor field-effect transistor are magnetically coupled to a two-dimensional electron gas, leading to an induced voltage. The major part of this voltage is proportional to the magnetoresistance, which is varied by changing the Landau-level filling. A second part is independent of the electron density and is tentatively attributed to the Hall-component of the resistivity tensor.

The critical fluctuations near ${\mathit{H}}_{\mathit{c}2}$(T) in the mixed phase of layered type-II superconductors are related to an equivalent system of classical particles with many-body ‘‘gauge’’ interactions. The scale invariance of this dense vortex plasma leads to a universal character of the vortex solid-liquid melting line where the transition to the superconducting state occurs. The relation to experimental situation in high-${\mathit{T}}_{\mathit{c}}$ and other layered superconductors and superconducting thin films is discussed.

We analyze the nature of the single-particle excitations and the collective modes in the nonmagnetic phase of a generalized t-J model to next to leading order in 1/N. We discuss the essential features of the spectral function of the t-J model and we evaluate it numerically for values of the parameters t,J, and of the doping level relevant to the copper-oxide planes.

A novel power law was found above 65 K in the I-V characterististics of ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_{\mathit{y}}$ single crystals with the magnetic field perpendicular to the c axis. At 80 K, the power-law exponent decreased sharply up to 1.5 T but remained nearly constant above it, suggesting an abrupt crossover to a different mechanism. An unusual field dependence of resistivity was also found, which cannot be explained by simple flux-flow theory. The above novel features of the Lorentz-force-independent dissipation can be consistently explained by a model based on two-dimensional vortex-antivortex pair breaking.

The first polarized infrared-reflectivity measurements of untwinned crystals of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathit{y}}$ as a function of y are reported. We separate the chain and plane contributions to the infrared conductivity, and find that for crystals with ${\mathit{T}}_{\mathit{c}}$≳50 K the prominent normal state midinfrared feature is associated with the chains. A threshold in the plane conductivity at ∼500 ${\mathrm{cm}}^{\mathrm{-}1}$ has a strong temperature dependence just below ${\mathit{T}}_{\mathit{c}}$ suggesting an association with the superconducting gap. Its temperature dependence above and below ${\mathit{T}}_{\mathit{c}}$ is quite similar to that of relevant NMR data, and is suggestive of gap development in the normal state.

We reduce a random-band-matrix (RBM) problem to a one-dimensional, nonlinear, supersymmetric, σ model. This reduction becomes exact in the limit b→∞, b being the effective bandwidth. We prove that ${\mathit{b}}^2$/N, N being the matrix size, is the relevant scaling parameter. When the mean value of diagonal elements increases linearly along the diagonal an extra scaling parameter arises. These conclusions are in agreement with recent numerical results.

We combine the cycle-expansion method with a functional equation to obtain highly excited semiclassical energy eigenvalues for chaotic Hamiltonian systems. Applications to the anisotropic Kepler problem and to a bounded billiard demonstrate the power of the method. The agreement with quantum results is surprisingly good even for highly excited states.

By relating scalar and vector couplings of the hyperons to the inferred empirical binding of the Λ hyperon in saturated nuclear matter, we obtain compatibility of this binding energy with neutron-star masses. Use of the observational constraint on the lower bound on the maximum neutron-star mass and the upper bound of the couplings that are compatible with hypernuclear levels, places bounds on the reduction in neutron-star mass that hyperons produce. For the best current estimate of nuclear-matter properties, the reduction in mass due to conversion of nucleons to hyperons is (0.71±0.15)${\mathit{M}}_{\mathrm{\odot }}$. Neutrons comprise a slight majority population ∼${\mathit{M}}_{\mathrm{\odot }}$ neutron stars with mass ∼1.5${\mathit{M}}_{\mathrm{\odot }}$.

We have measured the cross section as a function of invariant mass for isolated electron pairs produced in p¯p collisions at s=1.8 TeV for pair masses M>30 GeV/${\mathrm{c}}^2$. We find good agreement between the measured distribution and the standard-model prediction for the Drell-Yan production mechanism. Additional heavy neutral vector bosons (Z′) are excluded for ${\mathrm{M}}_{\mathrm{Z}\prime }$<387 GeV/${\mathrm{c}}^2$ (95% confidence level) assuming standard-model couplings. A lower limit of 2.2 TeV (95% confidence level) is placed on the electron-quark compositeness scale parameter ${\mathrm{\Lambda }}_{\mathrm{LL}}^{\mathrm{-}}$ associated with an effective contact interaction.

We have readjusted the short-range part of the Paris nucleon-antinucleon potential taking into account the new pp¯ data, in particular those from the CERN Low-Energy Antiproton Ring. Discrepancies between results of our earlier version and experimental data on charge-exchange cross sections are removed. Moreover, a significant improvement of the fit to cross sections and especially polarization in elastic scattering is obtained. Our analysis shows that the low-energy pp¯ data and the short-range NN¯ interaction are strongly dependent on each other.

We investigate the mechanism of pair creation in scalar QED from spatially homogeneous strong electric fields in 1+1 dimensions. Solution of the semiclassical field equations shows particle creation followed by plasma oscillations. We compare our results with a model based on a relativistic Boltzmann-Vlasov equation with a pair-creation source term related to the Schwinger mechanism. The time evolution of the electric field and the current obtained from the Boltzmann-Vlasov model is surprisingly similar to that found in the semiclassical calculation.

Attempts to reconcile a 17-keV neutrino with constraints from astrophysics and double beta decay have led to model Majorana neutrino mass matrices with vanishing (or nearly vanishing) electron-electron components. A simple parametrization is presented of the higher-order mass effects on the intermediate-state propagator through which 0ν ββ decay can still occur. For light-mass eigenstates, the 0ν and 2ν rates are proportional, with the ratio depending on a weighted sum over mass eigenstates 〈${\mathit{m}}_{\nu }^3$${\mathrm{〉}}_{\mathit{L}\mathit{L}}^{\mathrm{Maj}}$. Thus, model 0ν ββ decay rates can be predicted with confidence.

First experiments are described on the impact of additive noise on the ionization of Rb Rydberg atoms in microwave fields. Dynamical localization and its gradual destruction by noise are observed. The threshold and time dependence of the ionization process are investigated in the presence as well as in the absence of noise. Purely stochastic excitation induces a diffusionlike behavior that might be interpreted as restoration of the classical limit.

We have demonstrated an oscillating-gradient magnetic trap for confining cesium atoms in the lowest-energy spin state. In this state spin-flip collisions are energetically forbidden and thus the primary density- and temperature-limiting process for magnetic traps is eliminated. The atoms are initially collected in a vapor-cell optical trap, then repetitively tossed into a high-vacuum region, focused in three dimensions, and accumulated in the magnetic trap. An optical pumping scheme inserts each new batch of atoms into the magnetic trap without perturbing the atoms already trapped.

We predict that the intensity correlation between the Rayleigh line and a sideband of the fluorescence triplet displays destructive interference between opposite time orders of photon emission. We have measured this effect in natural barium. To our knowledge such an interference effect has not been observed before in atomic physics.

We have detected molecular coherence lasting nearly 9 times the collisional dephasing time in a Raman amplifier. Two laser pulses, separated in time, pumped a common set of hydrogen molecules, producing two Stokes pulses whose relative phase was measured interferometrically. The variance of this phase is a direct measure of the memory of the molecular coherence induced by the first scattering process. This experiment is capable of detecting a level of molecular coherence equivalent to between 15 and 50 vibrational phonons in the most strongly excited mode.

A scheme for measuring squeezing in resonance fluorescence from a single trapped and cooled ion is proposed, which is based on the observation of photon pair correlations after beating the fluorescence with a local oscillator. In addition to squeezing, anomalous moments and sub-Poissoinian photon statistics of the fluorescence contribute to the nonclasical behavior of the light in homodyne detection.

A phenomenon observed in a simple experiment with a diode laser is found to be a basis for powerful spectroscopy. In this spectroscopy, the laser frequency is neither scanned nor modulated. High-resolution spectra in a wide ratio-frequency range, such as Zeeman and hyperfine spectra in both of the ground and the excited states, are observed simultaneously by frequency analyzing the intensity fluctuation of the light transmitted through a sample cell. Demonstrating experiments are carried out with respect to the ${\mathit{D}}_1$ and ${\mathit{D}}_2$ lines of Cs and Rb atoms.

A theory is presented for the time-dependent breakdown of a network of spring (fuse) elements where the probability of breaking an element under load σ is ${\mathrm{\sigma }}^{\mathrm{\eta }}$. For all η, it predicts the system-size scaling of the number of broken elements at breakdown found in simulations. The breakdown is shown to be percolationlike for η≤2 but is due to the dominance of one large growing crack, despite the absence of a failure threshold, for η>2. This transition in fracture behavior and in scaling at η>2 is found to be directly related to the dependence of crack tip stress enhancement on the square root of crack size.

We present the results of a new calculational technique that evaluates the beam-beam force due to an arbitrary charge distribution. We find coherent instabilities that dominate at certain operating points and depend strongly on the degree of damping in the system. We conclude that while these resonances may play a significant role for colliders with low damping, with a careful choice of operating points they are unlikely to present a danger to colliders with greater damping, such as the new generation of high-luminosity heavy-quark factories currently under design.