[en] A novel substrate design is presented for scalable industrial production of filamentary coated conductors (CCs). The new substrate, called ‘two level undercut-profile substrate (2LUPS)’, has two levels of plateaus connected by walls with an undercut profile. The undercuts are made to produce a shading effect during subsequent deposition of layers, thereby creating gaps in the superconducting layer deposited on the curved walls between the two levels. It is demonstrated that such 2LUPS-based CCs can be produced in a large-scale production system using standard deposition processes, with no additional post-processing. Inspection of the conductor cross-section reveals that the deposited superconducting layer is physically separated at the 2LUPS undercuts. Filament decoupling is also seen in maps of the remanent magnetic field and confirmed by transport measurements. (fast track communication)

[en] Five sessions were held at the Sanibel Symposium 2008. 14 speakers, 5 chair persons for these 5 sessions and a number of posters are presented at the poster sessions.

[en] Dispersion relation for the CuO₂ hole is calculated based on the generalized t-t'-J model, recently derived from the three-band one. Numerical ranges for all model parameters, t/J=2.4 endash 2.7, t'/t=0.0 to -0.25, t double-prime/t=0.1 endash 0.15, and three-site terms 2t_N∼t_S∼J/4 have been strongly justified previously. Physical reasons for their values are also discussed. A self-consistent Born approximation is used for the calculation of the hole dispersion. Good agreement between calculated E_k and one obtained from the angle-resolved photoemission experiments is found. A possible explanation of the broad peaks in the experimental energy distribution curves at the top of the hole band is presented. copyright 1996 The American Physical Society

[en] In this work, we report on the effect of Y3+ doping on structural, mechanical and electrical properties of Bi-2202 phase. Samples of Bi2Sr1.9Ca0.1−xYxCu2O7+δ with x=0, 0.025, 0.05, 0.075 and 0.10 are elaborated in air by conventional solid state reaction and characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM) combined with EDS spectroscopy, density, Vickers microhardness and resistivity measurements. A good correlation between the variations of the bulk density and the Vickers microhardness with doping is obtained. The SEM photograph shows that the samples are composed of grains with a flat shape that characterizes the Bi-based cuprates. Quantitative EDS analysis confirms the reduction of Ca content and the increase of Y content when x is increased. The variation of resistivity with temperature shows that only samples with x=0, 0.025 and 0.05 present an onset transition to the superconducting state. The higher onset transition temperature is obtained for x=0.025 and is about 93.62K. The transition is wide and is realized in two steps confirming then the presence of the low Tc Bi-2201 phase in the samples. For x=0.075 and 0.10, a transition to a semiconducting state is seen at low temperatures. Some physical parameters are extracted from these curves and discussed. (Author)

No abstract available

[en] Epitaxial YBa₂Cu₃O_7-δ (013) films have been grown by pulsed laser deposition onto exact and vicinal (011) SrTiO₃ substrates. X-ray diffraction measurements showed that the films contained two mirror-related orientations when grown on exact (011) surfaces, but that a strong preference for only one of the two (013) orientations developed when the substrate surface was tilted by about 2 deg. toward the [011] SrTiO₃ direction. The inclination removed the two-fold symmetry of the surface to induce this preference, resulting in a film with (013) film parallel (011) substrate and [100] film parallel [100] substrate. Films with a single (013) orientation may offer some distinct practical advantages over other monocrystalline film orientations. (author)

[en] To reduce the coupling losses in superconducting structures, the twisting procedure for superconducting filaments and strands is usually applied. In superconducting tapes, the same effect can be achieved in some superconducting AC designs by taking advantage of the changing magnetic field direction with respect to the tape surface (internal twist). We calculate the coupling losses of twisted structures (filaments in strands, strands in cables) or striated YBa₂Cu₃O₇ coated conductors with additional normal plates on the tape connecting the superconductors. By enabling current sharing between the superconductors, such additional normal connections can considerably enhance the stability of the full conductor. Although the coupling losses increase slightly in these structures, it is shown that they can be held at an acceptably low level. This may be very important for superconducting structures with coupling losses that are not very high and therefore require better stability. The most favorable structure for coupling losses is emphasized. (paper)

[en] Using Gorkov's description of weakly coupled superconductors, together with a tight-binding model on two-dimensional lattices, we derive a pair of coupled equations for the mixed (s + id)-wave order parameters. It is shown that only in a small parameter region both the s- and d-wave states coexist with each other, whose order parameters have been obtained as a function of temperature. For the d-wave pairing, the van Hove singularity in the density of states is found to have more evident effect on enhancing the superconducting transition temperature and reducing the isotope-mass exponent, and thereby is more favorable to accounting for experimental data in cuprate superconductors. (orig.)

[en] Using the single flux motion model of Wang, Dong, and Ting (WDT) and taking into account both the pinning and thermal fluctuation, we perform a numerical study to investigate the dependence between the average pinning force anti F_p and the flux velocity v_L in different temperature regions in the mixed-state of high-T_c superconductors. The numerical simulation shows that there does not exist a unified scaling relation between anti F_p and v_L in the whole flux flow temperature region, but anti F_p and v_L keep a linear dependence in the lower temperature region of the negative Hall effect. The variations of the magnetic field or the pinning concentration do not change this linear relation. Employing this linear relation and WDT's theory, we naturally give the scaling law of ρ_xy ∝ ρ^β_xx with β ∼ 2. We also make a power fit for the data of anti F_p and v_L in the high-temperature region of both the negative and the whole positive Hall effect. Finally, we obtain anti F_p ∼ v^-ν_L with ν ∼ 1.5 to 2.0 for different magnetic fields and pinning concentrations. (orig.)

[en] An effective potential is proposed as a means to study the mechanism of pairing of high-T_c super-conductivity in the cuprates. The relation between size and energy of bound states evaluated in a first approximation is comparable to recent calculations obtained through quantum electrodynamics in (2+1) dimensions. In a second approximation, we consider that pairing occurs at the minimum of this effective potential, the problem being related to the quantum mechanical behavior of a particle described by polar coordinates in a plane. So, according to the present model, the topological constraint determined by the CuO₂ planes seems to be most relevant in the understanding of the pairing mechanism. (orig.)