Table of contents

A mean-field replica-type theory is presented for long-range Ising spin-glasses whose interactions can be written in the form J_ij = J_ij^IJ_ij^SK, where J^SK is a quenched Gaussian interaction, as in the SK spin-glass, and J^I is a deterministic matrix which defines the structure or inhomogeneity of the model and must have a finite rank in the thermodynamic limit. The spin-glass model proposed by Franz, Parisi and Virasoro (Europhys. Lett., 17 (1992) 5) can be written in this form, with J^I having rank 2, and is used as a case study to illustrate our theory. In the context of replica theory we also consider the stable states of this model, which appear continuously as the temperature is lowered.

We study the irreversible A + B → 0 reaction between particles which interact through short-range forces. The analysis leads to equations similar in structure to expressions which describe the growth of rough interfaces. We analyse the accumulation of particles under steady generation conditions. For screened electrostatic interactions in one dimension the numerical study of the theoretically derived equations displays an algebraic increase with time of the number of particles, n(t) ∼ t^γ with γ = 0.196 ± 0.011. We present theoretical arguments for γ = 1/5. On the other hand, for non-interacting particles one has γ = 1/4.

The theoretically predicted appearance of the temperature difference between the opposite sides of charging or discharging capacitors was observed for the first time. The capacitor of ferroelectric PbMg_1/3Nb_2/3O₃ crystal with Ni electrodes was charged applying the field to E = 10⁶ V/m with the time constant ≈ 10⁻⁵ s. The temperature difference at 300 K reached ≈ 10⁻⁴ K. The theoretical analysis of a "generalized Peltier effect" at the boundary of two arbitrary materials is done and it is shown that the experimental result can be considered as a "dieletric Peltier effect".

The K⁺-nucleon two-body potential is derived in the framework of the constituent quark model and it may provide reasonable explanation for the large K⁺-nucleon scattering phase shift of P-wave I = 0, J = 1/2 channel. On the basis of the derived K⁺-nucleon interaction, the real part of the K⁺-nucleus optical potential is constructed. Reasonable good agreement between theoretical cross-section and experimental data may be reached by requiring a weak imaginary part of the optical potential, as expected for the K⁺-nucleus scattering.

Diamagnetism in helium Rydberg atoms is studied near the ionisation threshold using constant scaled-energy laser spectroscopy. Quasi-Landau resonances in the Fourier transform of the energy spectrum are explained using the classical periodic-orbit theory. Long laser scans combined with a high-frequency resolution allow for a detailed comparison between experiment and theory. Resonances with a scaled action /π up to 20 are identified and reproduced with an accuracy of 0.015. It is demonstrated that interference effects between resonances should be taken into account.

The Super-ACO Free-Electron Laser (FEL) has been operated around 350 nm first at 600 MeV and more recently in June 1992 at 700 and 800 MeV, which is the highest energy for an FEL. Because of the energy increase, the laser lifetime is greater than ten hours and the output power has been enhanced by two orders of magnitude. In addition, with its good temporal stability, it appears to be a possible tool for users.

A fivefold quasi-crystalline structure in a liquid has been obtained with five ultrasonic beams coming together in water according to a regular pentagonal array. A pressure scanning by means of a hydrophone probe has been made to show in a direct way the evidence of the quasi-crystalline pressure structure. Acousto-optic diffraction experiments by using a laser beam have also been performed.

The problem of bulk self-diffusion in quasi-crystals is studied. We propose one possible mechanism for this process. Our scenario for diffusion is based on properties specific of the structure of quasi-crystals. The order of magnitude of the diffusion coefficient for a simple model of structure is estimated. The possibility that the proposed mechanism dominates over all other (standard) ones and the possible shape of the Arrhenius plot are discussed.

We have measured the magnetization of thick Nb_xSi_1−x films as a function of temperature (T) and magnetic field (H) near the metal-insulator (MI) transition. In the insulating phase the susceptibility χ ∝ T^−α with α ≈ 0.8 and both the T- and the H-dependence of χ are well described by a hierarchical spin-pairing model. In the metallic phase χ shows a similar power-law behavior with α ≈ 0.55, indicative of non-Fermi liquid behavior. We compare these results with similar measurements in doped semiconductors and with existing theories of the disordered insulating and metallic phases. The data suggest a decoupling of transport and magnetic behavior at the MI transition.

Based on finite-size scaling ideas a new approach to analyse the singularities associated with second-order phase transitions is presented. Under certain requirements, the method allows to derive an upper limit for the critical exponent from finite-size data that describe the system far away from the transition. By extrapolation the critical exponent ν is determined. As an example, the approach is applied to the metal-insulator transition in disordered systems. The result ν = 1.35 ± 0.15 is independent of the employed random distribution. With field theoretical arguments we discuss and generalize this result. Our results are consistent with the assumption that one-parameter scaling and universality are valid in the 3D Anderson model.

We consider a SNS junction, where the normal metal is taken to be in the quantum Hall regime. The induced supercurrent is carried by the edge states which are always extended. The coherence length along the direction of the edge state is determined by the drift velocity due to the surface electric field, and is much larger than the magnetic length. In a point contact junction, the critical supercurrent is independent of the positions of the leads, and depends only on the junction perimeter. We estimate the magnitude of this effect and comment on its experimental realizability.

Random telegraph voltage noise signals strongly dependent on externally applied magnetic field and transport current have been detected in c-axis-oriented BiSrCaCuO thin films at temperatures just below the onset of superconductivity. Signals appeared only in a narrow range of bias currents and associated magnetic fields. Such signals, already observed in granular YBaCuO films at helium temperatures, seem to be a universal feature of high-T_c superconducting films. Observed signals are consistently interpreted as an evidence of vortex hopping between two distinct pinning sites. Resistivity fluctuations and intrinsic SQUID detection are proposed as alternative mechanisms converting flux noise into random telegraph voltage signals.

Experimental evidence is presented for a competition between the superconducting and a structural transition in La_1.85−xNd_xSr_0.15CuO₄ as a function of the Nd content. At high Nd concentration (x ⩾ 0.18) a discontinuous, first-order structural transition is found, which destroys superconductivity and has a drastic influence on the normal-state transport properties. At lower Nd concentration (x < 0.18) a sharp superconducting transition occurs, which seems to suppress the structural phase transition.

The damage spreading technique is applied to ± J and Gaussian Ising spin glasses and ferromagnets in dimensions 3 and 4. By comparing with established values for the ordering temperatures in the spin glasses, it is shown that an independent damage spreading criterion can be used to obtain a reliable estimate of T_g, as long as precautions are taken concerning size effects. The physical significance of the damage spreading parameter is discussed.

We consider the hysteretic response of a system of two-dimensional planar spins in contact with a heat bath, to a uniform external magnetic field varying sinusoidally in time. The temperature is below the Kosterlitz-Thouless transition temperature T_KT. We show that for small H₀ and ω, the area of the hysteresis loop scales as (H₀ω)^α, where H₀ is the amplitude and ω the frequency of the external field, and α is an exponent which varies continuously from 1/2 to 16/31, as the temperature increases from zero to T_KT. This is an example of a driven dissipative system which shows self-organized criticality with continuously varying exponents.

It is shown that a particle with electric charge placed in a magneto-electric medium becomes a source of induced magnetic field the volume integral of whose divergence is non-zero. The particle with electric charge thus acquires a magnetic charge. It can also acquire an electric-dipole moment and all higher multipole moments forbidden by time reversal symmetry.

We investigate the effect of mixing two diblock copolymers of identical chemical structure but different molecular weight on self-assembled bilayers, using theoretical concepts of curvature elastic energy. Entropy and chain-chain interactions are found to favour ideal mixing in the two monolayers composing the bilayer, while curvature energy favours an inhomogeneous distribution of chains among the layers and, therefore, vesicle formation. The vesicle phase boundaries are determined as a function of mixture composition and molecular weight. We find that adding a small fraction of shorter chains to a copolymer bilayer is much more effective in destabilizing lamellar bilayers than the addition of a small fraction of longer chains.