Table of contents

We compute the probability, P, that the second photon of an atomic-cascade experiment, performed to test Bell inequalities, undergoes rescattering. In the case of the experiments of Aspect et al., we find P ≃ 0.1; hence, the possibility that photon rescattering be a "loophole" in the experimental refutation of local hidden-variable theories is ruled out.

The freezing transition of the one-component plasma (OCP) has been studied within the framework of the density functional theory of freezing. The inclusion of terms of third order in the density change is shown to be necessary to describe the transition.

Repulsive three-body forces in the presence of strong and very steep two-body attractive forces have a major effect on the phase diagram of a fluid: very low value of the critical density and strong asymmetry of the coexistence curve with an important singular contribution to the diameter. It is suggested that this is the origin of the known peculiarities of the phase separation taking place in micellar solutions.

We present a complete calculation of the lowest-order gluino-induced corrections to the weak form factors. In an exact supersymmetric theory the two tensorial form factors cancel out. In a realistically broken supersymmetry these corrections turn out to be small and possibly inadequate to bring out the signature of supersymmetry.

The recent experimental measurements for p and αα elastic scattering at high energies have shown that the Chou-Yang conjecture regarding the relationship between the electromagnetic and the hadronic form factor of a particle is only an approximation. A new ansatz has been proposed to obtain hadronic form factors of proton and the α-particle. These form factors have been used to explain the various characteristics of p, αα and pα elastic scattering at high energies.

Euclidean lattice fermions are examined in odd dimensions. The continuum flavours are identified and it is found that the flavours fall into two equal groups requiring inequivalent representations of the Dirac matrices. The relationship of this result to the parity transformation and the role of chiral symmetry are elucidated.

The neutral decay of the η'(958)-meson η' → ωγ → π⁰γγ → 4γ has been studied. The experiment has been performed in the IHEP 70 GeV accelerator with the multiphoton hodoscope spectrometer GAMS-2000. The measured branching ratio of the η' → ωγ decay (BR = 0.0330 ± 0.0036) is found to be in agreement with theoretical predictions.

We consider the autoionization of diatomic quasi-molecular states formed during collisions between multicharged ions and atoms. The N⁷⁺ He case is chosen as a typical example. We show that only double capture can lead to significant autoionization rates.

A recently proposed propensity rule for charge-cloud orientation in heavy-atom collisions is investigated experimentally. The scattered particle-polarized photon coincidence technique is used to study the excitation probability and electronic angular momentum of Mg⁺ ions undergoing 3s → 3p excitation in single collisions with He or Ar and impact parameters of typically (1 ÷ 2) a.u. The (1 ÷ 60) keV impact-energy range includes the region of maximum probability. The propensity rule is here strikingly confirmed and its range of validity illuminated.

We study the effect of a spatially periodic forcing on the appearance of one-dimensional periodic patterns. Analogies with commensurate-incommensurate transitions and the periodic forcing of self-oscillating systems are pointed out. We also give a concrete example of spatial quasi-periodicity and interpret some recent experimental results.

Amorphization by solid-state interdiffusion of bilayers consisting of a Ni single crystal and polycrystalline Zr has been studied by Rutherford-backscattering spectrometry and X-ray diffraction analysis. This type of bilayer samples forms an amorphous phase, starting at the interface in the same way as polycrystalline diffusion couples. The lack of a significant nucleation barrier is in contrast to the recently reported study, where a Zr single crystal and a polycrystalline Ni film did not interdiffuse.

In this letter the construction of a quasi-periodic three-dimensional tiling with one-dimensional translational symmetry is described. The tiling is generated by the projection method. This quasi-lattice can serve as a model of the structure of the decagonal phase of Al-Mn alloys, which has been recently discovered. The present construction is closely related to the projection of two- and three-dimensional Penrose tilings. A comparison is made with the model proposed by Ho.

Activated processes at surfaces–like desorption or oxidation–exhibit thermal anomalies at phase transitions of the underlying substrate. Inter alia, such singularities in the case of a continuous transition are caused by the critical slowing down in the substrate, which leads to pronounced memory effects in the viscosity coefficient. Therefore, we apply a non-Markovian analog of Kramers' classical rate theory. As a result, the anomalies can be expressed in terms of critical exponents associated with the critical surface behaviour.

The influence of a symmetry breaking field on the triangular 3-q incommensurate phase of quartz is discussed. The appearance of a 1-q stripe phase between the β phase and the 3-q phase is expected when a uniaxial stress σ is applied in the (001) plane. In the (σ, T)-plane the 1-q phase is bound by two transition lines which meet at T_i. Elastic-neutron-scattering experiments demonstrate that such a stress-induced 1-q phase is actually observed in quartz and the experimental phase diagram is in qualitative agreement with theory.

The heat capacities C_p of a number of Ge_xSe_1-x amorphous alloys have been measured through the glass transition temperature T_g. In each case C_p rises from a value slightly larger than the classical limiting value of 3R in the glass to a value in the supercooled liquid which is larger by up to 40%. For x = 0.125, 0.2, 0.25 and 0.35 values of C_p in the liquid follow a common curve, identical within the experimental error to that of liquid Se. To explain this insensitivity to structure, a theory is presented for the liquid in which the contributions to the internal energy from vibrational and configurational modes are separated. By identifying the configurational modes with local stresses, an explicit expression can be calculated for the heat capacity which agrees well with experiment.

We compare inelastic electron tunnelling measurements by Yamaguchi and Nishina for a GaSe thin slab with the surface projected total phonon density calculated by a linear-chain model fitted to recent inelastic atom scattering data of GaSe (001). We conclude that in case of relevant differences between bulk and surface-perturbed phonon densities only the latter can be significantly compared with inelastic electron tunnelling spectra. Moreover, our previous observation that the dynamics of surface layers in GaSe is considerably different from that of the bulk is confirmed by a completely independent experimental technique.

Measurements are reported of the derivatives dM/dH and dM/dT of the magnetization of a superconducting network near the superconducting transition temperature in a weak transverse magnetic field. The a.c. susceptibility dM/dH exhibits sharp peaks at integer and fractional number of flux quanta per cell as expected from the phase diagram (H, T) of the network. In contrast, the dM/dT measurements reveal distinct features, characteristic of the equilibrium state below the superconducting transition. These results are compared to recent theoretical predictions for the mixed state of a superconducting network.

We investigate theoretically the behaviour of anisotropic superconductors under uniaxial stress, using the Landau expression for the free energy. It is found that, in many cases, the normal superconducting phase transition splits into two, or even three, second-order transitions. The experimental observation of such a splitting would give much information about the form of the superconducting order parameter of the system.

We report high-field measurements carried out on the pressure-induced super-conductor EuMo₆S_8-YSe_Y. Our results show that the phenomenon of magnetic-field-induced superconductivity (MFIS) occurs in this compound if the critical superconducting temperature T_c is correctly adjusted to a value close to 7 K. Besides, as foreseen by the multiple pair-breaking theory already used in the analysis of the H_c2-data on the pseudoternary Eu_XSn_1-XMo₆S₈, we also observe that MFIS occurs in EuMo₆S_8-YSe_Y at higher fields and higher temperatures than in the former.