International Journal of Modern Physics B

The temperature dependence of the NMR spin-lattice relaxation time is analyzed for preliminary evaluation of the correlation time of the local dynamics of the polymeric chain, for the molten polyisoprene and some polyisoprene-CCl₄ solutions. Complementary information concerning this dynamics were obtained from the analyze of the ESR spectra recorded from the nitroxide molecules (2, 2, 6, 6, tetramethyl piperidin-1-yloxyl) dissolved in the polyisoprene-CCl₄ solutions.

Multi-band superconductivity is investigated by using two-particle Green's function techniques, and equations for coupled states are derived in the framework of a two-band model. These results suggest that superconductivity appears, even if electron–electron interaction is positive. We also present a cooperative mechanism for multi-band superconductivity.

A model is introduced for two reduced BCS systems which are coupled through the transfer of Cooper pairs between the systems. The model may thus be used in the analysis of the Josephson effect arising from pair tunneling between two strongly coupled small metallic grains. At a particular coupling strength the model is integrable and explicit results are derived for the energy spectrum, conserved operators, integrals of motion, and wave function scalar products. It is also shown that form factors can be obtained for the calculation of correlation functions. Furthermore, a connection with perturbed conformal field theory is made.

La_0.5Ca_0.5MnO₃ (LCMO) thin films grown on SrTiO₃ substrate with different thickness were investigated using high resolution X-ray diffraction, small angle reflectivity, and atomic force microscope (AFM). All the films are demonstrated to be c-axis oriented. The surface and interface structure of the films were obtained. It was found that the surface morphology of the films strongly depends on the thickness, and the film will crack when the thickness of the film reach a critical thickness. The surface roughness of the films increases with the thickness. The interface between the films and the substrates are very clear. There exists a non-designed cap layer on the surface of the LCMO layer.

One-, two- and three-dimensional structures A_xB_y can be characterized by the numbers T₁, T₂ and T₃ of the nearest, next-nearest and third neighbors of the same kind. A smaller number of structures at the border of the T₁, T₂, T₃ structure map is stabilized by enthalpy compared to an increased number of entropy stabilized structures away from the border. Structures with T₁ = 2 nearest neighbors of all A atoms are suitable for infinite chains of polymers like (CH)_∞, (CHCH₂)_∞ or (CH₂)_∞.

We deposited copper phthalocyanine (CuPc) films on (100) silicon wafers by means of a vacuum evaporation method and investigated the dependence of X-ray diffraction pattern on film thickness. We concluded that the planar molecule of CuPc is stacked normal to the substrate within 700 nm from an interface. Above 700 nm, four types of nearly parallel stacking were also observed. These results show the spontaneous formation of the two-layer structure in CuPc films thicker than 700 nm.

The pseudogap structure in low energy excitation in cuprates appears below a temperature and the spectral density exhibits strong wave-vector dependence. An electronic model that emphasized the coupling of carrier in Cu-O with phonon is examined for pseudogap. The electron–phonon interaction originates from the modulation of on-site and hopping energy and leads to spontaneous Jahn–Teller-like distortion and pseudogap below a critical temperature. At low temperature the spectral density has two-peak structure about the Fermi level for all k along Γ-M whereas such structure exists along Γ-X for small k only. The magnitude of pseudogap shows strong k-dependence — maximum along Γ-M and vanishes along Γ-X. These features emphasize the role of electron–phonon interaction in formation of pseudogap.

Dk values at the diffusion of CO₂ through microporous PTFE of 1 to 7 × 10^-7cm²s^-1 in the concentration range from 4 × 10^-4 to 0.22 g/l CO₂ are determined using a simple, fast and reliable potentiometric method. The method is based on the least-squares fitting of the potential versus time response of a self made CO₂ sensitive Severinghaus type sensor with PTFE as a gas-permeable membrane. The obtained results are in good agreement with other reported literature data, both experimental or calculated ones using molecular dynamics simulations. The proposed technique is very sensitive especially at low concentrations of gas and may be used for the study of other polymeric membranes too.

Density of state calculation performed previously for the Harper-equation by Wannier, Obermair and Ray [Phys. Status SolidiB93, 337 (1979)] are updated analytically and numerically. One considers both the influence of anisotropy and commensurability parameters. The main point of our generalization is to account for a multiplicity parameter describing the amount of coprime realizations of the commensurability parameter.

The dispersion relations of energy bands in solids are characterized by their density of states, but a given density of states may originate from various band structures. We show how a spherically symmetric dispersion can be constructed for any one-band density of states. This method is applied to one-, two- and three-dimensional systems. It also serves to establish that any one-band spectrum with finite bandwidth can be obtained from a properly scaled dispersion relation in the limit of infinite dimensions.

The thermal noise of DC Josephson current in the superconducting leads coupled with a quantum dot system is investigated, and the general thermal current noise formula is derived in the presence of Zeeman field. The resonant structure versus gate voltage and Zeeman energy are displayed. Novel structures associated with the bound state and normal energy state are obtained. As the temperature is low, the Andreev reflection plays an important role in thermal noise and this provides new channels for electron to tunnel. However, if the temperature is high enough, the thermal noise due to Andreev reflection is trivial compared with the normal transport one. The thermal noise versus phase difference is also given to exhibit the temperature dependence. The Fano factor versus phase is much larger than 1 if the temperature is nonzero.

PZT(Zr:Ti=52:48) ceramics can be modified by Gd³⁺, giving compositions Pb_1-xGd_x- (Zr_0.52Ti_0.48)1-x/4 O₃ with x = 0.00, 0.01, 0.5, 1, 2, 6 and 10 mole percent. X-ray diffraction patterns show that all PGZT samples are of tetragonal structure and the highest doping should be no more than 2 mole percent Gd at which impurity unreacted oxides start to appear. ESR spectra of PGZT's indicate that Gd³⁺ can enter both A and B sites of the perovskite structure instead of only A site as widely believed. As a result, the tetragonality (c/a ratio) first increases and reaches a maximum at x ≅ 0.8 mole percent and drops as Gd³⁺ enters more A sites. The doping should, however be limited to one mole percent as overdoping proves detrimental to the dielectric and piezoelectric properties of PGZT. The dielectric constant (1 kHz) of the poled samples reaches a maximum value of 1150 at x = 0.02 while the largest d₃₃ value of 160 pC/N is achieved at only lightly doped 0.01 mole percent. Furthermore, the Gd doping has a drastic effect on Q_m and the dissipation factor DF — the former drops sharply while the latter increases with x.

In a recent work we have introduced a novel approach to study the effect of weak nonlinearity in the transfer function on the information transmitted by an analogue channel, by means of a perturbative diagrammatic expansion. We extend here the analysis to all orders in perturbation theory, which allows us to release any constraint concerning the magnitude of the expansion parameter and to establish the rules to calculate easily the contribution at any order. As an example we explicitly compute the information up to the second order in nonlinearity, in presence of random Gaussian connectivity and in the limit when the output noise is not small. We analyze the first and second order contributions to the mutual information as a function of the nonlinearity and as a function of the number of output units. We believe that an extensive application of our method via the analysis of the different contributions at distinct orders might be able to fill a gap between well-known analytical results obtained for linear channels and nontrivial treatments which are required to study highly nonlinear channels.

We presented here the phase diagrams and the influence of the external electric field on the lyotropic liquid crystal phase (LLC) for some binary and pseudoternary systems based on surfactants. Binary systems are of the type surfactant/water (S/W) and the pseudoternary systems are of the type surfactant/oil/water (S/O/W). Two surfactants have been used: the lauryl alcohol ethoxilated with 11 molecules of ethylene oxide (LA11EO), which is a nonionic compound, and a mixture of LA11EO with the cationic surfactant named alkyl C₁₂–C₁₄-dimethyl-benzyl ammonium chloride. Based on these two types of surfactants, pseudoternary systems were prepared. Pine oil has been used as the oil. The region where the LLC phase appears depends on the concentration of the surfactant and that of the pine oil, respectively. It is strongly influenced by the nature of the surfactant and by the presence of the pine oil for the same type of surfactant. The influence of the external electric field, investigated by measuring the electric current appearing in the samples for different concentrations of surfactant and pine oil was found to be more important in the case of the systems based on the nonionic-cationic mixture of surfactants. The results are discussed in terms of a theoretical model based on the local thermal equilibrium approach for systems running nonstatic processes.