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Arce, R., F. de la Cruz, and H. J. Fink. "Model relating superconductive penetration depth and metallurgical phase separation in amorphous La70Cu30." Solid State Communications 42, no. 8 (1982): 575–577.
Abstract: A model is proposed to account for the large increase in the measured penetration depth of superconducting, amorphous La70Cu30 when the specimens are annealed sufficiently long near, but below, the crystallization temperature. It is suggested that a metallurgical phase separation occurs with domain dimensions in the submicrometer range. Penetration depth measurements as a function of temperature in a weak magnetic field are a useful tool to detect changes in phase separation in high-K materials.
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Guimpel, J., and F. de la Cruz. "Electrical resistivity of amorphous Zr70Cu30 and the Kondo like model." Solid State Communications 44, no. 7 (1982): 1045–1046.
Abstract: Electrical resistivity measurements of amorphous Zr70Cu30 as a function of the concentrations of two level systems show that a Kondo like theory cannot explain the observed temperature dependence.
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Arce, R., F. de la Cruz, and J. Guimpel. "Superconducting behavior of amorphous Zr70Cu30." Solid State Communications 47, no. 11 (1983): 885–887.
Abstract: Measurement of the Meissner penetration depth, λ(T) were made in amorphous Zr70Cu30 samples. The results indicate that this amorphous alloy behaves as a BCS superconductor with 2Δ(0)+45 degree rulekTc = 3.8, where Δ(0) is the superconducting energy gap at T=0 and Tc the critical temperature. It is also concluded that the low energy excitation, TLS, characteristics of amorphous material does not contribute to Tc.
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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., 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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Osquiguil, E., V. L. P. Frank, and F. de la Cruz. "Two dimensional collective flux pinning in melt spun superconducting amorphous Zr70Cu30." Solid State Communications 55, no. 3 (1985): 227–230.
Abstract: We have measured the critical currents in melt spun amorphous Zr70Cu30 and their evolution with heat treatment. We found that the pinning forces may be interpreted in terms of the Larkin-Ovchinnikov two dimensional collective pinning theory.
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Luzuriaga, J., C. D'Ovidio, and F. de la Cruz. "Ideal two dimensional flux pinning induced by annealing in superconducting amorphous Zr75Rh25." Solid State Communications 57, no. 9 (1986): 753–756.
Abstract: By annealing amorphous Zr75Rh25 prepared by melt spinning an ideal behaviour of the critical current was observed, in which the measured pinning forces are seen to follow the two dimensional Larkin-Orchivnikov theory. In the region where this theory is valid the changes in the pinning forces can be explained by the changes in the superconducting matrix and it can be assumed that the pinning centers do not change with the heat treatment.
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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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Núñez Regueiro, M., M. A. Izbizky, and P. Esquinazi. "Thermal conductivity and “disorder” in high temperature superconductors." Solid State Communications 67, no. 4 (1988): 401–404.
Abstract: We analyze the controversial thermal conductivity results on high temperature superconductors by scaling the data with material parameters to compare them to other materials with similar behaviour. We show that they have the same general features observed in amorphous and disordered crystalline materials. Possible origins of the disorder are discussed.
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Osquiguil, E., R. Decca, G. Nieva, L. Civale, and F. de la Cruz. "La1.80 Sr0.20 CuO4-delta a clean limit superconductor." Solid State Communications 65, no. 6 (1988): 491–494.
Abstract: The electrical resistivity of the superconductor La1.80Sr0.20Cu04-? has been measured in a wide range of temperatures as a function of oxygen and vacuum heat treatments. The resistivity changes reversibly orders of magnitude with oxygen concentration. There is no sign of saturation at high temperatures, even for samples where the resistivity is increased by heat treatment in vacuum. Using the experimental data and general arguments it is concluded that the ceramic superconductors are high ? materials in the clean limit.
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