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A procedure for the numerical prediction of the microwave nonlinear behavior (intermodulation products, degradation of quality factors, etc.) of TM010 disk resonators has been developed. The procedure is based on relating a very general description of HTS nonlinearities with the circuit elements of a nonlinear radial transmission line. This radial transmission line is then analyzed using the harmonic balance algorithm. Successful cross-checks are performed by comparing simulations with theoretical results obtained for a specific model of HTS nonlinearity. The application of this procedure to the determination of nonlinear material parameters from disk resonator measurements is illustrated as well as its use for simulating filters with several inter-coupled disks. Correction: J. Mateu, IEEE Trans. Appl. Superconduct., vol. 11, pp. 135–138, Mar. 2001. On p. 137 of the above paper, the first sentence of the paragraph immediately following equation (14) should read as follows.

Cu K-edge absorption (EXAFS and XANES) spectroscopy has been used to investigate instantaneous local lattice fluctuations in the cuprate superconductors. We find an abrupt change in the instantaneous local lattice fluctuations across the charge-stripe ordering temperature. Here we report this order parameter like behavior of the local lattice fluctuations in a model charge stripe ordered La1.48Nd0.4Sr0.12CuO4 system and argue that the change in the local lattice structure is a response function of the charge-stripe ordering in these materials. The results provide a direct evidence for electron-lattice interactions to be an important ingredient for the charge-stripe ordering in the cuprate superconductors.

The anomalous behavior observed in the optical spectral weight (W) of the cuprates provides valuable information about the physics of these compounds. Both the doping and the temperature dependences of Ware hardly explained through conventional estimates based on the f-sum rule. By computing the optical conductivity of the doped Hubbard model with the Dynamical Mean Field Theory, we point out that the strong correlation plays a key role in determining the basic features of the observed anomalies: the proximity to a Mott insulating phase accounts simultaneously for the strong temperature dependence of W and for its zero temperature value. (c) 2007 Elsevier B.V. All rights reserved.

Les oxydes supraconducteurs à température critique élevée, à base de bismuth et comportant 2 ou 3 plans cuivre, sont synthétisés suivant diverses méthodes. Nous réalisons ensuite l'élaboration par frittage de matériaux composites aléatoires, constitués d'une dispersion de grains supraconducteurs de phase au bismuth 2212 dans une matrice d'argent. Nous étudions la résistivité électrique et l' aimantation en effet d'écran des matériaux en fonction de la température, du champ magnétique et de la concentration en phase supraconductrice. Les comportements observés sont interprêtés dans le cadre d'une approche phénoménologique impliquant la notion de "liens supraconducteurs faibles". Enfin, nous tentons de relier, par des mesures de spectroscopie de photoelectrons X, les informations statistiques obtenues aux caractéristiques chimiques des jonctions intergranulaires.; non disponible

The formation of the textured Bi,Pb(2223) in mono- and multifilamentary tapes is described as a result of several reactions, involving an intermediate phase Bi,Pb(2212), which is formed as a solid solution of the initial phase Bi(2212), the latter having a monoclinic superstructure. For Bi,Pb(2223) tapes, a direct correlation between the degree of texturing of the initial Bi(2212) grains after rolling (before reaction) and of the current carrying Bi,Pb(2223) platelets (after reaction) is shown. The difference between the critical current densities of pressed and rolled tapes is discussed by comparing the maximum applicable uniaxial pressure with the local pressure exerted by the rolls. The optimization of the complex preparation process leading to long rolled Bi,Pb(2223) tapes is discussed. The lateral distribution of the transport critical current densities in monofilamentary Bi,Pb(2223) tapes with jc(77K, 0T) = 28000A/cm2 shows a marked minimum at the center and a maximum at the sides, the highest value reaching 54000A/cm2. At 4.2K and 14T, the same tape reached the value jc=75000A/cm2. For long (>1m), rolled multifilamentary Bi,Pb(2223) tapes with 7 and 19 cores, critical current densities up to 23000A/cm2 have been obtained. The field dependance of jc is essentially the same as for monofilamentary tapes. The variation of the critical current density in Bi,Pb(2223) tapes as a function of B and T is presented and discussed within the "railway switch" model.

While there is increasing evidence for antiferromagnetic (AF) ordering in the Cu–O planes of high-Tc superconductors, either static or fluctuating, there is no direct evidence so far for the charge stripes that should separate the AF domains. In the optical response of La2−xSrxCuO4, for x values in the superconducting range, we identify strong far-infrared peaks whose energy, width, and intensity are consistent with a scenario of charge stripe dynamics in the Cu–O planes.

L' étude d'une technique originale de croissance cristalline, basée sur l'utilisation d'un échangeur thermique et nommée HEM (Heat Exchanger Method), a été entreprise. Un dispositif expérimental a été développé et optimisé. La modélisation des échanges thermiques a conduit a l'élaboration d'un code de calcul numérique. Ce dernier est valide par confrontation des résultats de la simulation aux données expérimentales obtenues lors de la croissance d'un matériau école, le germanium. Le champ d'application de la technique HEM a alors été étendu à l'obtention de céramiques texturées du supraconducteur à haute température critique YBa2Cu3O7-x. Après une étude de la microstructure des textures, un mécanisme de texturation est proposé. Enfin, des cristaux du compose NaMgF3 (perovskite) sont obtenus par HEM. Leur étude en température, par observation des domaines ferroélastiques et par spectroscopie Raman, révèle l'existence d' une seule transition de phase.; non disponible

Temperature dependent positron lifetime measurements in Y1-xPrxBa2Cu3O7-δ are discussed, and reveal positron trapping at low temperature (T

International audience; Homogeneous Tl1.8Ba2CaCu208 ceramics were synthesized by a novel route, starting from Tl2Ba205 precursors and using high gas pressures. This method allows tight control of thallium losses, resulting in dense, large-grained samples with sharp superconducting transitions above 105 K. Results of a characterization by X-ray diffraction, optical micrographs and micro-probe analysis are presented, together with selected physical properties.

The general principles of the low-temperature spectroscopic cathodoluminescence (LTSCL) technique in the scanning electron microscope (SEM) are outlined. CL microscopy and spectroscopy are now being extended in new directions. Analysis of the intrinsic CL from quantum well materials by LTSCL is proving valuable for microcharacterization and such work can be expected to expand rapidly. The main, early CL results in this exciting field are summarized here. In geology, CL microscopy, without spectroscopy, is widely used via electron-beam attachments to light microscopes and the addition of spectral analysis to these studies is overdue. Much CL from minerals and ceramics comes from trace amounts of rare earth or transition metal ions, so the nature of this important type of emission is briefly described. Results on ceramic materials illustrating the advances in the field and the distinctive nature of the rare earth and transition metal ion emission bands are reviewed. The fascinating high Tc superconducting ceramics emit CL and there are a number of papers reporting the emission spectra of these materials, but no theoretical interpretation of the information is yet available. A new factor in the situation is the commercial availability of complete LTSCL systems, removing one of the main obstacles to the adoption of the technique by more laboratories.

Using the slave boson approach to treat the Ud → ∞ limit for the Coulomb repulsion on the copper site in the p-d model we give a short account on various charge fluctuation modes. The effect of the slave boson field adjustment on the strength and the Fermi surface effects for k = 0 and k = (π, π) charge transfer modes is discussed. The implications for the screening of the corresponding electron-phonon couplings is also pointed out.

Angle resolved one-hole spectra have been calculated starting from a realistic tight-binding Hamiltonian and including correlation and surface effects. The hole self-energy has been evaluated using the t -matrix approximation for the hole-hole scattering. To account for surface effects the local density of states of the outermost atomic layers has been determined assuming an ideal termination of the crystal and a non polar basal plane surface. The theoretical curves allow one to assign the main features of the spectra at high symmetry points of the Brillouin zone, except for the peak observed at 8.5 eV binding energy. It is suggested that the discrepency may arise from the neglecting of the k -dependence in the self-energy or from the extrinsic nature of the peak.

A procedure for the numerical prediction of the microwave nonlinear behavior (intermodulation products, degradation of quality factors, etc.) of TM010 disk resonators has been developed. The procedure is based on relating a very general description of HTS nonlinearities with the circuit elements of a nonlinear radial transmission line. This radial transmission line is then analyzed using the harmonic balance algorithm. Successful cross-checks are performed by comparing simulations with theoretical results obtained for a specific model of HTS nonlinearity. The application of this procedure to the determination of nonlinear material parameters from disk resonator measurements is illustrated as well as its use for simulating filters with several inter-coupled disks.

Numerical database systems have recently become available online. Their enhanced search capabilities and fast retrieval of data make them a valuable tool in research. In particular, CRYSTDAT which is a search and analysis system for NBS CRYSTAL DATA has proven to be powerful in the identification of crystalline materials. In conjunction with a single-crystal x-ray diffractometer, a qualitative as well as quantitative phase determination is easily performed. The use of CRYSTDAT will be illustrated in several examples.