Lopez, D., E. F. Righi, G. Nieva, F. de la Cruz, W. K. Kwok, J. A. Fendrich, G. W. Crabtree, and L. Paulius. "Amplification of the c-axis vortex correlation by twin-boundary pinning at the vortex liquid-solid phase transition." PHYSICAL REVIEW B 53 (1996): R8895.
Abstract: Transport measurements using the dc flux transformer configuration together with c-axis resistance data in clean and twinned YBa2Cu3O7-δ single crystals show that vortices are localized by the twin-boundary potential. The results support the existence of a divergent tilt modulus [D. R. Nelson and V. M. Vinokur, Phys. Rev. B 48, 13 060 (1993)] in a liquid that freezes into a Bose glass
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López, D., E. F. Righi, G. Nieva, F. de la Cruz, W. K. Kwok, J. A. Fendrich, G. W. Crabtree, and L. Paulius. "Discontinuous Onset of the c-axis Vortex Correlation at the Melting Transition in YBa2Cu3O7." In Proceedings of the 10th Anniversary Hts Workshop on Physics, Materials and Applications, edited by B. Batlogg, 411. Singapore: World Scientific Publishing Company, 1996.
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López, D., G. Nieva, and F. de la Cruz. "In- and out-of-plane vortex correlations in YBa2Cu3O7." Physical Review B 50 (1994): 7219.
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López, D., E. A. Jagla, E. F. Righi, E. Osquiguil, G. Nieva, E. Morré, F. de la Cruz, and C. A. Balseiro. "Dynamic softening of vortex lines in YBa2Cu3O7−δ single crystals." Physica C: Superconductivity 260, no. 3-4 (1996): 211–216.
Abstract: Transport measurements in the mixed state of oxygen-deficient YBa2Cu3O7−δ single crystals using the flux transformer configuration show that the flux liquid changes with increasing anisotropy from strongly correlated to uncorrelated in the field direction. For intermediate coupling, the current inducing loss of vortex correlation has a maximum near the irreversibility temperature. Thus, an effective softening of vortex lines with decreasing temperature is detected. We propose a simple model that accounts for this behavior by including the effects of the pinning potential on the dynamics of vortices.
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López, D., R. Decca, and F. de la Cruz. "Topological pinning and flux flow in ceramic superconductors." Solid State Communications 79, no. 11 (1991): 959–962.
Abstract: The transport current dissipation in the high Tc superconducting ceramic La1.85Sr0.15CuO4−δ shows a sin2 Θ voltage dependence where Θ is the angle between the transport current and the magnetic field. This result and the experimental evidence of an angle independent critical current cannot be explained by the conventional description of flux motion in homogeneous type II superconductors. The results are analyzed in the framework of a granular system where pinning is induced by the topological distribution of current flowing through a multiply connected medium. The dissipation in the superconducting state is found to be due to two additive contributions, one induced by the movement of magnetic flux and the other associated to dissipation in the Josephson junction.
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López, D., G. Nieva, F. de la Cruz, Henrik Jeldtoft Jensen, and Dominic O’Kane. "Flux cutting in YBa2Cu3O7-δ single crystals: Experiment and phenomenological model." Physical Review B 50 (1994): 9684.
Abstract: We measured the current-induced loss of vortex correlation in YBa2Cu3O7-δ crystals using the pseudo-dc-flux-transformer geometry. We find that the current density Jcut at which the top and bottom voltage drops differ is a linear function of temperature, is independent of pinning, and depends on the thickness of the sample. This thickness dependence strongly suggests that the electrical current flows at the surface of the sample. The observed behavior with temperature, magnetic field, and thickness is described by a phenomenological model.
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López, D., G. Nieva, and F. de la Cruz. "Long range correlations of the vortex structure in YBCO single crystals." Physica C: Superconductivity 235-240, no. 4 (1994): 2575–2576.
Abstract: Transport measurements in the mixed state of YBa2Cu3O7 single crystals using the “DC flux transformer” configuration show that the glass-liquid phase transition at the irreversibility line, TI(H), behaves as a three dimensional vortex phase transition. These results together with resistance measurements in the c direction show that the vortex correlation across the sample is destroyed at a temperature Tth(H), higher than TI(H). The sample thickness dependence of Tth(H) suggest that in the real thermodynamic phase transition (infinite sample), the long range correlation in the ab plane as well in the c direction is lost at the single temperature TI(H).
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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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Guimpel, J., C. Monton, N. Haberkorn, and F. de la Cruz. "Magnetic behaviour of superconductor/ferromagnet metallic and perovskite based superlattices." physica status solidi (c) 4, no. 11 (2007): 4174–4180.
Abstract: We present a study of the magnetic behaviour of superconducting/ferromagnetic superlattices, both for metallic and perovskite based systems. In the first case we find that the response is determined by the ferromagnetic layer regime. If these layers are very thin, no ferromagnetism is observed, but the superconducting layers are decoupled, and the superlattice behaves as a stack of independent superconducting films. For thicker ferromagnetic films, ferromagnetism is established and the effective field resulting from the superposition of stray and applied fields dominates the superconducting response of the superlattice. For the perovskite based superlattices, the physical properties are more affected by interface disorder. In this case we have found that the behaviour can be interpeted as charge carrier transfer between both materials, inducing a change in the magnetic character of the manganite. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
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Guimpel, J., M. E. de la Cruz, F. de la Cruz, H. J. Fink, O. Laborde, and J. C. Villegier. "Size dependence of the Superconducting critical temperature and fields of Nb/Al multilayers." Journal of Low Temperature Physics 63, no. 1-2 (1986): 151–165.
Abstract: The critical temperatureT cof Nb/Al multilayers decreases as the total sample thicknessd Tis decreased while the thickness of each Nb and Al layer is kept constant. To understand this behavior, models based on the proximity effect and on weak two-dimensional (2D) localization are employed. The latter uses a characteristic length, the thermal diffusion length, in relation tod Tto obtain 2D behavior and leads to a reasonable explanation ofT c(d T). It is also found that the slope atT c(d T) of the critical magnetic field perpendicular to the layers is independent ofd Twhen the Nb and Al layer thicknesses are kept constant. The angular dependence of the critical field is also measured.
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