Superfluid and vortex dynamics in a fractal system were investigated by measuring the complex sheet impedance of a wire network of interconnected Sierpinski gaskets exposed to a weak magnetic field. By probing the network response over a range of length scales covering four stages of hierarchy in the gaskets, we find strong evidence for unusual scaling of the vortex energy ${\mathit{U}}_{\mathit{n}}$ with the size ${\mathit{r}}_{\mathit{h}}$ of the loops, ${\mathit{U}}_{\mathit{h}}$∝${\mathit{r}}_{\mathit{h}}^{\mathrm{-}\mathrm{\zeta }}$ with ζ=ln5/3/ln2, predicted by theory.

An excess low-voltage conductance is observed in Nb-InGaAs contacts at low temperatures and interpreted as being due to a pair current across the superconductor-semiconductor interface. This is the first observation of a pair current, a nonequilibrium manifestation of the proximity effect, in junctions having one electrode which is not a superconductor. A model is presented which accounts for the observed behavior. In addition to the pair current, it is demonstrated that these junctions exhibit excess conductance due to Andreev scattering.

Small-capacitance tunnel junctions show single-electron effects and, in the superconducting state, the coherent tunneling of Cooper pairs. We study these effects in a system of two voltage-biased Josephson junctions in series. Novel features show up in the I-V characteristics, in particular, pronounced structures at subgap voltages. These are due to combined quasiparticle and pair tunneling and to higher-order Cooper-pair tunneling processes. Several of them have been observed in experiments.

We have measured the full voltage dependence of the quantum conductance and quantum susceptance which arise, respectively, from the dissipative and nondissipative quasiparticle tunneling currents in a superconductor-insulator-superconductor tunnel junction. Using a standing-wave technique, we measured the admittance of the tunnel junction at 87 GHz. The admittance is the sum of the quantum conductance and the quantum susceptance. We report the first direct observation of the reactive quasiparticle singularity which is evident in the quantum susceptance.

We report critical-current measurements in all high-${\mathit{T}}_{\mathit{c}}$ superconducting-normal-superconductor junctions using ${\mathrm{Y}}_{0.6}$${\mathrm{Pr}}_{0.4}$${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ (with ${\mathit{T}}_{\mathit{c}\mathit{N}}$=40 K) as the normal metal. Above ${\mathit{T}}_{\mathit{c}\mathit{N}}$, we find a clear exponential dependence of ${\mathit{I}}_{\mathit{c}}$ on the thickness of the barrier which is characteristic of the proximity effect. The order-parameter decay length is about 120 Å for T>60 K, and it diverges as ${\mathit{T}}_{\mathit{c}\mathit{N}}$ is approached. We estimate that ${\xi }_0$ for this material is 80±25 Å.

The random-matrix-theory approach to the avoided-crossings probability distribution for quantum chaotic systems is proposed. Analytical results are obtained for all three (orthogonal, unitary, and symplectic) universality classes of physical systems as well as for systems with partially broken time-reversal invariance. The numerical experiments on the kicked-top model give results in excellent agreement with the theoretical predictions.

We analyze the dynamic behavior of large two-dimensional systems of limit-cycle oscillators with random intrinsic frequencies that interact via time-delayed nearest-neighbor coupling. We find that even small delay times lead to a novel form of frequency depression where the system decays to stable states which oscillate at a delay and interaction-dependent reduced collective frequency. For greater delay or tighter coupling between oscillators we find metastable synchronized states that we describe analytically and numerically.

Results for d=2 percolation allow one to determine exactly the critical exponents for a polymer undergoing the special surface transition, while its bulk is at the FTHETA’ point. ${\gamma }_1$=8/7 and ${\mathrm{\phi }}_{\mathit{s}}$=8/21 are the entropic and the crossover surface exponents, respectively. On the other hand, exact enumerations analysis leads to conjecture ${\gamma }_1$=4/7 at an ordinary FTHETA’ point. This strongly supports universality of FTHETA and FTHETA’ points. Similar exact results are obtained for a multicritical walk in the presence of correlated percolation vacancies.

For multiparticle systems we formulate the notions of signal locality (i.e., absence of faster-than-light signaling) and Einstein-Bell locality (or local realism) and obtain inequalities between experimental correlation functions to test them. Quantum theory obeys signal locality but violates Einstein-Bell locality by a factor $2^{\left(\mathit{n}\mathrm{-}1\right)/2}$ for n-particle systems.

We analyze the possibility of solving the strong CP problem by imposing parity symmetry. Some simple realizations of such a scheme are given and interesting phenomenological and cosmological consequences are discussed.

The disappearance of transverse collective flow for ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$${+}^{27}$Al collisions is studied with an improved Boltzmann-Uehling-Uhlenbeck equation. For collisions at impact parameters less than 3 fm, the predicted energy of balance, ${\mathit{E}}_{\mathrm{bal}}$, is very sensitive to the in-medium nucleon-nucleon cross section, but insensitive to the equation of state. At larger impact-parameter collisions, the sensitivities to both the in-medium nucleon-nucleon cross section and the equation of state at subnuclear density becomes comparable. Comparisions with experimental data indicate an in-medium nucleon-nucleon cross section in the range of 25–45 mb.

The (α+d) breakup of 60 MeV ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ scattered from ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ has been measured inside the grazing angle for c.m. energies of the fragments between 100 keV and 1.5 MeV. We find the integrated cross sections to be in agreement with Coulomb excitation theory, but the angular correlations of nonresonant breakup exhibit significant deviations from this theory. This shows that the measured breakup cross section cannot be related by first-order Coulomb excitation theory to the astrophysically relevant ${}_{}{}^4{}_{}{}^{}\mathrm{He}$(d,γ${)}^6$Li capture reaction.

We study supersymmetric quantum mechanics with particular emphasis on factorization as a key to understanding the recently discovered isospectral γ ray cascades seen in neighboring superdeformed nuclei. Explicit realization of the general algebraic approach leads to state doubling in the odd-A nucleus.

In this work, we analyze the influence of non-Markovian effects on a pulsed time-delayed four-wave-mixing experiment. By using a perturbative approach the density matrix equations are solved for a medium modeled by two-level systems and excited by short pulses. We show that the intensity of the diffracted light can be expressed as a simple function of the bath memory function. This demonstrates the interest of such an experiment to get information on the bath.

We report the first precise measurements of parity nonconserving (PNC) optical rotation in atoms, carried out on the 876-nm M1 transition in bismuth. We obtain ${\mathit{R}}_{\mathit{i}}$=Im(E$1_{\mathrm{PNC}}^{\mathit{i}}$/M1)=(-10.12±0.20)×${10}^{\mathrm{-}8}$, where E$1_{\mathrm{PNC}}^{\mathit{i}}$ is the E1 amplitude mixed into the transition by the nuclear spin-independent PNC interaction. The result is in excellent agreement with the standard model of the electroweak interaction. The amplitude of nuclear spin-dependent PNC rotation is found to be less than 1.5×${10}^{\mathrm{-}2}$ of that due to the nuclear spin-independent interaction.

It is shown that photons in a polar crystal with a high nonlinearity can feel an attractive effective interaction by exchange of virtual phonons. A coherent state is unstable with respect to such an interaction, and a superguiding state is formed through the association of photons in pairs with opposite wave vectors and spins. The photon pairs travel without scattering attenuations. If the photons propagating in a wave guide enter the superguiding state, the wave guide exhibits an ultralow energy loss.

rf power in the lower-hybrid-frequency range is shown to produce plasma of density in the ${10}^{13}$ ${\mathrm{cm}}^{\mathrm{-}3}$ range in the small toroidal heliac SHEILA by launching helicon waves. Measurements of wave dispersion and mode structure confirm that an m=1 helicon mode is launched inside the highly asymmetric plasma confined in the device. The suggestion that the main energy-transfer mechanism is by Landau damping is strongly supported by the experimental data.

Brillouin scattering in an organic glass-forming liquid up to a pressure of 12 GPa is reported. The onset of the unrelaxed regime is indicated by a distinct maximum in the acoustic attenuation at a pressure ${\mathit{P}}_{\mathrm{\alpha }}$, above which weak shear modes are resolved. Sound velocity data are fitted in a self-consistent way which accounts for relaxation by combining the ‘‘universal’’ Vinet equation of state with an expression for the dynamical modulus. This analysis yields the pressure dependences of the relaxed and unrelaxed moduli, relaxation time, and density over the pressure range studied.

By use of conformal field theory, we calculate the energies of one or more curved domain boundaries at two-dimensional critical points. We find the interaction of two separated boundaries of the same type to be weakly attractive, and proportional to the square of an operator-product expansion coefficient. In a strip of width L, the interaction vanishes exponentially with separation, over a distance set by L. It is also small for nearby domains when one of them is much smaller than L. Many-body interaction energies are weak as well.

We measure for the first time the average mechanical response of a III-V mixed crystal with a two-mode behavior, ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Al}}_{\mathit{x}}$As, to a vibrational excitation at frequencies in the gap between the two optical-phonon branches. These frequencies are selected by the boundary conditions applied to the optical phonons confined in the GaAs layers of GaAs/${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Al}}_{\mathit{x}}$As superlattices. We measure their variations with the composition of the alloy layer. The alloy lattice dynamics predicted in the coherent potential approximation is perfectly verified: The gap is shown to be divided into GaAs- and AlAs-type ranges. At the cutoff frequency the average damping becomes infinite.