Table of contents

Entanglement may be considered a resource for quantum information processing, as the origin of robust and universal equilibrium behaviour, but also as a limit to the validity of an effective potential approach, in which the influence of certain interacting subsystems is treated as a potential. Here we show that a closed three-particle (two protons, one electron) model of a He⁺-ion featuring realistic size, interactions and energy scales of electron and nucleus, respectively, exhibits different types of dynamics depending on the initial state: For some cases the conventional approach, in which the nucleus only appears as the center of a Coulomb potential, is valid, in others this approach fails due to entanglement arising on timescales as small as 10⁻⁵s. Eventually, the system can even show signatures of thermodynamical behaviour, i.e. the electron may relax to a maximum local entropy state which is, to some extent, independent of the details of the initial state.

The uniform asymptotic approximation for large η of the exact 3D Coulomb scattering wave function Ψ_c is obtained. This approximation is deduced by using the closed-form expressions of Ψ_c and of its components Ψ_cdpw and Ψ_cdow in terms of the Coulomb wave functions and their derivatives, obtained in the present letter.

Gamma-Ray Bursts (GRBs) production is discussed in the framework of the Brans-Dicke (BD) theory of gravity. We derive the effective potential and the acceleration of a scalar particle propagating in a gravitational field described by BD theory. The rate of the energy radiated by charged particles is also calculated. Constraints on parameters entering the BD theory are fixed in order to reproduce the typical outputs energy of GRBs.

We study and explore the symmetry properties of fermions coupled to dynamical torsion and electromagnetic fields. The stability of the theory upon radiative corrections as well as the presence of anomalies are investigated.

We study the probability, P_S(t), of a cluster to remain intact in one-dimensional cluster-cluster aggregation when the cluster diffusion coefficient scales with size as D(s) ∼ s^γ. P_S(t) exhibits a stretched exponential decay for γ < 0 and the power laws t^−3/2 for γ = 0, and t^{−2/(2 − γ)} for 0 < γ < 2. A random walk picture explains the discontinuous and non-monotonic behavior of the exponent. The decay of P_S(t) determines the polydispersity exponent, τ, which describes the size distribution for small clusters. Surprisingly, τ(γ) is a constant τ = 0 for 0 < γ < 2.

We consider a population of parametrically excited globally coupled oscillators in a weakly nonlinear state. The instabilities of collective modes lead to a traveling-wave regime, where intensities of oscillations of each oscillator vary periodically in time. For large excitation amplitudes a frozen state with nearly uniform oscillation intensities is observed.

Transient phase dynamics, synchronization and desynchronization which are stimulus-locked (i.e. tightly time-locked to a repetitively administered stimulus) are studied in two coupled phase oscillators in the presence of noise. The presented method makes it possible to detect such processes in numerical and experimental signals. The time resolution is enormous, since it is only restricted by the sampling rate. Stochastic stimulus locking of the phases or the n:m phase difference at a particular time t relative to stimulus onset is defined by the presence of one or more prominent peaks in the cross-trial distribution of the phases or the n:m phase difference at time t relative to stimulus onset in an ensemble of post-stimulus responses. Unlike the presented approach, both triggered averaging (where an ensemble of post-stimulus responses is simply averaged) and cross-trial cross correlation (CTCC) lead to severe misinterpretations: The oscillators' coupling may cause a transient anti-phase clustering of the post-stimulus responses. Triggered averaging cannot distinguish such a response decorrelation from a mean amplitude decrease of the single responses. CTCC not only depends on the oscillators' phase difference but also on their phases and, thus, inevitably displays "artificial" oscillations that are not related to synchronization or desynchronization.

Considering the multiple scattering from a highly inhomogeneous medium occupying a half-space, a solution of the Bethe-Salpeter equation is obtained using the Wiener-Hopf method. The result obtained generalizes the well-known Milne solution to the case of anisotropic single-scattering in the P₁ approximation. The dependence of the coherent backscattering on the anisotropy parameter is derived directly and shown to differ essentially from that predicted by the diffusion approximation. Initial slopes of coherent backscattering as well as temporal correlation function are found to be in fair agreement with known experimental data.

A model of Boussinesq convection in a fast rotating spherical layer with the free-rotating inner core is considered. To solve the problem, two sets of equations are used. First, we solve the original Navier-Stokes equation and thermal-flux equation on the coarse grid. The small-scale flow features are described in terms of the shell model technique. The influence of small scales on large-scales is taken into account by means of effective viscosity, which is calculated from the spectral energy flux defined in the shell model. The properties of the turbulent spectrum is considered.

X-ray microdiffraction (μ-XRD) is used for the first time to probe the liquid crystal (LC) ordering in confined LCs. We report on the direct observation of the director field in single droplets of nematic LCs embedded in a solid polymeric matrix (polymer-dispersed LCs). The bipolar configuration is identified in droplets with radius R ⩽ 1 μm. Both the director distribution function and the droplet order parameter are obtained from diffraction patterns and the results are in excellent agreement with theoretical calculations. This technique is unique in its application to dispersed mesophases in that it allows to probe the local (μm length scale) LC ordering. The possibility of focusing measurements on single droplets eliminates the problems connected with averaging, which are typical of other techniques. Our results prove that μ-XRD is a novel and valuable tool in the study of confined LCs and open new exciting opportunities for future investigations.

We have investigated the vortex state in a superconducting dice network using the Bitter decoration technique at several magnetic frustrations f = ϕ/ϕ₀ = 1/2 and 1/3. In contrast to other regular network geometries where the existence of a commensurate state was previouly demonstrated, no ordered state was observed in the dice network at f = 1/2 and the observed vortex-vortex correlation length is close to one lattice cell.

When a corrosive solution reaches the limits of a solid sample, a chemical fracture occurs. An analytical theory for the probability of this chemical fracture is proposed and confirmed by extensive numerical experiments on a two-dimensional model. This theory follows from the general probability theory of extreme events given by Gumbel. The analytic law differs from the Weibull law commonly used to describe mechanical failures for brittle materials. However, a three-parameter fit with the Weibull law gives good results, confirming the empirical value of this kind of analysis.

A 1 μm diameter Pb crystallite, supported on Ru(001), was equilibrated and imaged by scanning tunneling microscopy at 298 K. The vicinal shapes close to the (111) facet at the top of the crystal were analyzed in detail to determine the critical shape exponent and the step-step interaction energy as well as the interaction constant of the potential. An average shape exponent of 1.47 and a step interaction energy of ∼ 32 meV/Ų were obtained. The exponent is very close to the theoretically predicted universal value of 3/2 and as such provides clear evidence for a dominant 1/x² step interaction potential. The ratio of step free energy to step interaction energy for Pb at 298 K is ∼ 0.34.

We study the growth of gas bubbles surrounded by liquid during the phase separation of a pure CO₂ sample quenched from one-phase to two-phase region of the phase diagram by rapid cooling in microgravity. The vicinity of the critical point ensures slowing-down of the growth process. The bubble growth by coalescence is modified by local laser heating. It induces a thermocapillary (Marangoni) effect that attracts the bubbles towards the center of the beam. At the beginning of the phase separation, a bubble is trapped there and "captures" the surrounding bubbles. The growth exponent for the central bubble radius is close to 0.5, while that for the other bubbles is 1/3. We present a theoretical model that explains the experimental data and justifies that the temperature can vary along the gas-liquid interface in a pure fluid during its phase separation.

We have studied the chemical potential shift in La_{1 − x}Sr_xMnO₃ as a function of doped hole concentration by core-level X-ray photoemission. The shift is monotonous, which means that there is no electronic phase separation on a macroscopic scale, whereas it is consistent with the nanometer scale cluster formation induced by chemical disorder. Comparison of the observed shift with the shift deduced from the electronic specific heat indicates that hole doping in La_{1 − x}Sr_xMnO₃ is well described by the rigid-band picture. In particular no mass enhancement toward the metal-insulator boundary was implied by the chemical potential shift, consistent with the electronic specific-heat data.

We have performed a photoemission study of La_{1 − x}Sr_xTiO_{3 + y/2} near the filling-control metal-insulator transition (MIT) as a function of hole doping. The spectral intensity at the chemical potential (μ) and the mass enhancement factor deduced from the bandwidth show qualitatively the same doping dependence as the specific coefficient γ except for near the MIT, where additional mass renormalization may occur in the vicinity of μ. Upon antiferromagnetic ordering, spectral weight transfer occurs from the coherent to the incoherent parts, which we associate with the partial gap opening at μ.

The interaction energy of three adsorbates on a surface consists of the sum of the three pair interactions plus a trio contribution produced by interference of electrons which propagate the entire perimeter, d₁₂₃, of the three-adsorbate cluster. Here we investigate this triple-adsorbate interaction that is mediated by the isotropic Shockley surface-state band found on noble-metal (111) surfaces. Our experimentally testable result depends on the s-wave phase shift, δ_F ≠ 0, characterizing the standing-wave patterns seen in scanning-tunneling microscopy (STM) images. Compared with the adsorbate-pair interactions, and in contrast to bulk-mediated interactions, the trio contribution has a slightly weaker amplitude and asymptotically decays slightly faster, ∝ d₁₂₃^−5/2. It also has a distinctive oscillation period dependent on d₁₂₃. We finally compare the asymptotic description with exact model calculations.

According to the crystal structure of MgB₂ and band structure calculations quasi–two-dimensional (2D) boron planes are responsible for the superconductivity. We report on critical fields and resistance measurements of 30 nm thick MgB₂ films grown on MgO single crystalline substrate. A linear temperature dependence of the parallel and perpendicular upper critical fields indicates a 3D-like penetration of magnetic field into the sample. Resistivity measurements, in contrast, yield a temperature dependence of fluctuation conductivity above T_c which agrees with the Aslamazov-Larkin theory of fluctuations in 2D superconductors. We consider this finding as an experimental evidence of two-dimensional nucleation of superconductivity in MgB₂.

We formulate the Dynamical Mean-Field Approximation equations for the double-exchange system with quenched disorder for arbitrary relation between Hund exchange coupling and electron bandwidth. Close to the ferromagnetic-paramagnetic transition point the DMFA equations can be reduced to the ordinary mean-field equation of Curie-Weiss type. We solve the equation to find the transition temperature and present the magnetic phase diagram of the system.

We have employed a new experimental configuration to measure ferromagnetic X-ray resonance exchange scattering (XRES) from a EuS single crystal. Using polarisation analysis we could achieve a magnetic-scattering intensity stronger than charge scattering resulting in an asymmetry ratio as large as R_a = 0.67 at the Eu_LII edge. By a combined refinement of the dependencies of the scattered intensity on the energy and the applied magnetic field we could uniquely determine spectroscopic information such as the 5d conduction band exchange splitting = 0.27(1) eV.

We report an Inelastic Neutron Scattering (INS) study of the fully deuterated molecular compound K₆[V₁₅^IVAs₆O₄₂] · 9D₂O (V₁₅). Due to geometrical frustration, the essential physics at low temperatures of the V₁₅ cluster containing 15 coupled V⁴⁺ (S = 1/2) is determined by three weakly coupled spin-(1/2) on a triangle. The INS spectra at low energy allow us to directly determine the effective exchange coupling J₀ = 0.211(2) meV within the triangle and the gap 2Δ = 0.035(2) meV between the two spin-(1/2) doublets of the ground state. Results are discussed in terms of deviations from trigonal symmetry and Dzyaloshinskii-Moriya (DM) interactions.

Magnetoresistance in the spin-density wave (SDW) state of (TMTSF)₂PF₆ is known to exhibit a rich variety of the angular dependencies when a magnetic field B is rotated in the b' − c*, a − b' and a − c* planes. In the presence of a magnetic field the quasiparticle spectrum in the SDW with imperfect nesting is quantized. In such a case the minimum quasiparticle energy depends both on the magnetic-field strength |B| and the angle θ between the field and the crystal direction a, b' or c*. This approach describes rather satisfactory the magnetoresistance above T* ≈ 4K.

The dynamical properties of the small fullerene cluster (C₆₀)₁₄, confined between two parallel graphite walls, have been studied using a molecular-dynamics (MD) simulation method. An interesting instance of behaviour of C₆₀ molecules in this environment has been discovered. For a range of distances d between the graphite walls (2.2 nm < d < 2.7 nm) the fullerenes form two monolayers parallel to the graphite surfaces (no migration of molecules between layers). The monolayers slide one against the other and perform a torsional motion.

The spontaneous formation of lipid vesicles (liposomes) in aqueous lecithin/bile salt mixtures is studied using time-resolved static and dynamic light scattering. These measurements reveal a strong dependence of the kinetic rates and end-state liposome properties on total amphiphile concentration and, even more pronounced, on ionic strength. The observed trends contradict equilibrium calculations, but are in quantitative agreement with a kinetic model that we present. This model identifies the key kinetic steps during vesicle formation: rapid formation of disc-like intermediate micelles, growth of these micelles and closure to form vesicles. This work offers conclusive evidence for kinetic rather than thermodynamic control of the end-state properties.

Erratum of Europhys. Lett.58 p. 202