Correa, V. F., G. Nieva, and F. de la Cruz. "Vortex softening: Origin of the second peak effect in Bi2Sr2CaCu2O8+delta." PHYSICAL REVIEW LETTERS 87, no. 5 (2001): 057003.
Abstract: Magnetic hysteresis and transverse ac permeability measurements in Bi2Sr2CaCu2O8+delta allow a comparative analysis of the critical current with the elastic response of vortex structures, in equilibrium with their pinning potential, in the field and temperature region where the second peak is detected. This study provides strong evidence that the second peak has its origin in changes of the elastic equilibrium properties of the vortex structures.
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Correa, V. F., J. A. Herbsommer, E. E. Kaul, F. de la Cruz, and G. Nieva. "Order-disorder transition and the zero-dimensional vortex pinning regime in Bi2Sr2CaCu2O8+delta." PHYSICAL REVIEW B 63, no. 9 (2001): 092502.
Abstract: We make a comparative study between the ab plane's dc critical current and the ac transverse magnetic permeability μ(perpendicular to) in the Campbell limit for optimally doped and overdoped Bi2Sr2CaCu2O8+delta samples. We focus attention on the low-temperature region [T/T-c(0) < 0.25], where the transition to the zero-dimensional Larkin limit is detected by the critical current as well as by a rapid change of the Labusch parameter with temperature. The order-disorder transition, characterized by the second peak in magnetization, disappears in the presence of this zero-dimensional pinning regime.
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Grigera, S. A., E. Morré, E. Osquiguil, G. Nieva, and F. De la Cruz. "Nonlocal transport properties and size effects in heavily twinned YBa2Cu3O7-delta single crystals." Solid State Communications 107, no. 7 (1998): 335–339.
Abstract: We demonstrate experimentally that when the vortex correlation length in the liquid state becomes of the order of the sample thickness, size effects dominate the transport properties of the macroscopic vortex structures, implying a nonlocal response in the transformer experiments.
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Rodríguez, E., C. Duran, J. Luzuriaga, F. de la Cruz, and C. Fainstein. "Anomalous behaviour of the vortex structure in Bi4Ca2Sr4Cu4O16+y measured with a vibrating reed at low magnetic fields." Physica C: Superconductivity 165, no. 3-4 (1990): 315–320.
Abstract: The response of the vortex structure in ceramic samples of Bi4Ca2Sr4Cu4O16+y has been measured by means of a vibrating reed technique in magnetic fields below 0.2 T. An anomally in the response of the reed is seen at temperatures of around 30 to 40 K, well below the critical temperature, indicating a transition similar to that attributed to a melting of the Flux Line Lattice. There is a shift in the temperature at which the anomaly is detected when one increases the driving force on the reed, while the dissipation shows a maximum associated to the transition which scales with the square of the applied magnetic field. Comparison with magnetization measurements shows that there is non-zero critical current at the same temperature where the anomalous behaviour is detected with our technique.
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de la Cruz, M. E., E. J. P. Godfrin, F. de la Cruz, and C. de Allende. "Superconducting intermediate state in cadmium." Solid State Communications 18, no. 6 (1976): 747–749.
Abstract: Perpendicular magnetic critical fields for cadmium foils were measured to thicknesses below the temperature dependent coherence length. The presence of supercooling indicates first-order thermodynamic transitions for all samples. A modification of Davies' model leads to a good fit of the experimental data.
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Esquinazi, P., M. E. de la Cruz, A. Ridner, and F. de la Cruz. "Heat treatment effects in amorphous metals: Zr70Cu30 and La70Cu30." Solid State Communications 44, no. 6 (1982): 941–944.
Abstract: We measured the electrical resistivity (4–300 K), superconducting critical temperature and thermal conductivity (0.5–7 K) of the amorphous metals Zr70Cu30 and La70Cu30. Heat treatments below crystallization temperature induced changes in these properties. In particular, in the first stage of the annealing of Zr70Cu30 there are systematic changes in the thermal conductivity and the critical temperature, while the electrical resistivity remains constant. We show that there is no simple correlation between the thermal conductivity processes in the low temperature and plateau regions. We also show that the thermal conductivity of as quenched La70Cu30 is typical of amorphous metals, contrary to information previously reported.
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Esquinazi, P., M. E. de la Cruz, and F. de la Cruz. "Heat treatment effects in La70Cu30 amorphous system." Physica B+C 108B, no. 1-3 (1981): 1215–1216.
Abstract: It is shown that superconductivity is a useful tool to investigate the evolution of the amorphous state, when heat treatment below the crystallization temperature.
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Kaufman, H. L., and F. de la Cruz. "Fluctuation induced diamagnetism in aluminum." Solid State Communications 9, no. 20 (1971): 1729–1732.
Abstract: The magnetic field and temperature dependence of the magnetization of bulk aluminum near the normal-superconductor transition has been measured. Due to the large amount of supercooling in one of the samples it was possible to extend the measurements well below the critical temperature. A comparison of the experimental results with theory is presented.
Résumé
Nous avons mesuré la dépendance en champ magnétique et en température de la magnétisation d'un échantillon massif d'aluminium au voisinage de la transition état normal-état supraconducteur. Grâce au ‘supercooling’ important d'un des échantillon, nous avons pu étendre nos mesures bien au dessous de la température critique. Nous comparons les résultats expérimentaux à la théorie.
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de la Cruz, F., H. J. Fink, and J. Luzuriaga. "Temperature dependence of the superconducting giant-vortex state. Theory and Experiment." Physical Review B 20, no. 5 (1979): 1947–1959.
Abstract: When a type-I superconductor with a surface nucleation field Hc3(T)>Hc(T) (thermodynamic critical field) is thermally cycled in an axially applied magnetic field H0 between the temperatures T(Hc3) and about T(Hc), experiments show that the magnetization changes reversibly. The latter is diamagnetic near T(Hc3) but can be paramagnetic just above T(Hc). This behavior is explained by assuming that the fluxoid quantum number b is fixed at the transition from the normal to the superconducting state and retained at lower temperatures. The value of b is determined almost entirely by the flux at the transition which is enclosed by a contour located at a distance ξ1.7 from the surface inside the cylinder (ξ is the coherence length). The temperature variation of the order parameter f at the surface of the cylinder, the magnetization m, and the temperature at which m=0 for f≠0 are calculated for R>>ξ. Conservation of the fluxoid quantum number, while T is varied causes the two opposing surface currents to become imbalanced. This is the source of the observed para- and diamagnetism.
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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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