Arce, R., L. Civale, J. Luzuriaga, J. Guimpel, and F. de la Cruz. "Surface normal regions in superconducting Zr70Cu30 induced by thermal relaxation." Solid State Communications 48, no. 12 (1983): 1027–1030.
Abstract: Penetration depth measurements show that thermal heat treatment in amorphous Zr70Cu30 induces a normal region 5000 Å thick at the surface of ultrarapid quenched ribbons. Upper critical field measurements indicate that the new induced phase is a normal one while the rest of the sample remains as a homogeneous superconducting phase.
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Civale, L., and F. de la Cruz. "Anomalous behavior of superconducting samples with a fixed number of vortices." Physical Review B 36, no. 7 (1987): 3560–3564.
Abstract: We report an anomalous reversible temperature dependence of the magnetization of amorphous type-II superconductors. The experimental results were obtained studying the vortex pinning in samples with very low vortex concentration. The anomaly is shown to be a consequence of the lack of flux quantization in finite samples.
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Civale, L., F. de la Cruz, and J. Luzuriaga. "Critical temperature and density of states in amorphous Zr70Cu30." Solid State Communications 48, no. 4 (1983): 389–391.
Abstract: By means of thermal heat treatment of amorphous Zr70Cu30 it is shown that the induced decrease in critical temperature is followed by a reduction in the electronic density of states of the same magnitude as that obtained by changing the Cu concentration. This result indicates that the density of states is the fundamental microscopic parameter determining the superconducting behavior.
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Civale, L., G. Pasquini, P. Levy, G. Nieva, D. Casa, and H. Lanza. "Time relaxation of persistent currents in YBa2Cu3O7−x crystals with columnar defects." Physica C: Superconductivity 263, no. 1-4 (1996): 389–395.
Abstract: We have measured the persistent currents and their time relaxation in YBa2Cu3O7−x single crystals with correlated disorder introduced by irradiation with high-energy heavy-ions. For vortex density lower than the defect density, and for applied fields either parallel or nonparallel to the columnar defects, we find clear evidence of a pinning-crossover between a regime of strong individual pinning at low temperatures and a regime of weaker collective pinning at high temperatures. We explore the vortex dynamics above and below this crossover.
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Civale, L., G. Pasquini, P. Levy, G. Nieva, and H. Lanza. "AC susceptibility of pinned vortices in YBa2Cu3O7 crystals with correlated disorder." Advances in Superconductivity: VIII: Proceedings of the 8th International Symposium on Superconductivity (1996): 553.
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Civale, L., H. Pastoriza, F. de la Cruz, J. Guimpel, G. Nieva, J. M. Heintz, O. Durmeyer, and J. P. Kappler. "Meissner fraction of insulating samples of oxide superconductors." Solid State Communications 72, no. 4 (1989): 341–344.
Abstract: The tendency towards superconducting granularity with sample degradation is a common feature of oxide superconductors. We present magnetic, transport and calorimetric results in LiTi$2Ο4$ which show that the topological tendency to segregate the superconducting state into islands surrounded by thin insulating layers is related to the structure of the material rather than to a mechanism associated to high T$_C$. We emphasize that insulating samples with small Meissner fraction can have a superconducting volume fraction close to unity.
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Civale, L., H. Safar, and F. de la Cruz. "Percolation and glass behavior in ceramic superconductors: oxygen effects." Modern Physics Letters B 3, no. 2 (1989): 173–181.
Abstract: It is shown that small variations of oxygen content in La1.8Sr0.2CuO4−δ can be used to control the reversible and irreversible magnetization temperature dependence of the superconducting state. A grain bond model is appropriate to describe the superconducting response of the ceramics. The study of the temperature dependence of the magnetization and the resistive transition temperature, in a slightly deoxygenated sample, show that the reversible superconducting state is strongly correlated to superconducting percolation. Deoxygenation has been shown to be an excellent technique to study the time evolution of metastable states induced by currents in the bonds and or in the grains. It is shown that superconducting grains are not correlated to ceramic grains.
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de la Cruz, F., M. E. de la Cruz, L. Civale, and R. Arce. "Hybridization effects between d and s bans in amorphous materials." In Proceedings of LT-17, 1301. Elsevier Science Publishers BV, 1984.
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Dediu, V. I., Q. D. Jiang, F. C. Matacotta, P. Scardi, M. Lazzarino, G. Nieva, and L. Civale. "Deposition of MBa2Cu3O7-x thin films by channel-spark method." Superconductor Science and Technology 8, no. 3 (1995): 160.
Abstract: Channel-spark pulsed electron beam deposition (CS), a new deposition method based on a simple and inexpensive system, has been used for preparation of high-quality GdBa2Cu3O7-x, Gd1-xEuxBa2Cu3O7-x and YBa2Cu3O7-x thin films epitaxially grown on NdGaO3 and SrTiO3 substrates. Typical critical temperatures for zero DC resistance lie in the intervals 87-89 K for Y-based films and 91.0-92.6 K for Gd- and GdEu-based ones. The transition widths for the best films are less than 0.5 K. The critical current densities reach the values of 3*106 A cm-2 at 77 K, zero field.
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Esparza, D. A., C. A. D'Ovidio, J. Guimpel, E. Osquiguil, L. Civale, and F. de la Cruz. "The granular nature of bulk superconductivity at 40K in La1.8Sr0.2CuO4." Solid State Communications 63, no. 2 (1987): 137–140.
Abstract: We have measured the electrical resistivity, magnetic flux expulsion and critical fields of the new high temperature superconductor La1.8Sr0.2CuO4 after different heat treatments. Our data show that the complete flux expulsion in these samples is consistent with the presence of shielding currents induced in multiple connected structures. The magnetization measurements indicate that the lowest field where flux penetrates into the sample should not be taken to be the bulk Hcl. It is shown that the absolute value of the electrical resistivity and its temperature dependence are not correlated with the superconducting critical field and temperature. We discuss the behaviour of the superconducting parameters and their relation with the electrical resistivity.
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