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Pastoriza, H., and P. H. Kes. "Direct shear probe of vortex lattice melting in Bi$2$Sr$2$CaCu$2Ο8$ single crystals." Phys. Rev. Lett. 75, no. 19 (1995): 3525–3528.
Abstract: We report results of transport measurements on single crystals of the superconductor Bi$2$Sr$2$CaCu$2Ο8$ where weak pinning channels in a strong pinning environment were artificially introduced. The experimental data show that in this material the shear viscosity of the vortex liquid phase suddenly increases upon decreasing the temperature supporting the melting scenario. We also found that below the phase transition the data are in good agreement with plastic ow of a vortex solid through the channels.
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Pastoriza, H., and P. Martinoli. "Phase transitions in triangular arrays of XY spins with variable coupling." Czechoslovak Journal of Physics 46, no. S4 (1996): 1905.
Abstract: We present Monte Carlo simulations in a generalized uniformly frustrated triangular-lattice model of XY spins. The frustration is varied by changing the relative strength, $\etha$, of one of the bonds of the unit well. We found that the ground state transforms from ferromagnetic to anti-ferromagnetic along the variable bond direction for a critical value of $\etha=-1/\sqrt(3)$. Simultaneously, the phase transition towards the paramagnetic state at high temperatures changes from purely Kosterlitz-Thouless like to one of mixed character
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Pastoriza, H., H. Safar, E. F. Righi, and F. de la Cruz. "Flux creep in YBa$2$Cu$3Ο7$ single crystals near $TC$." Physica B 194-196 (1994): 2237–2238.
Abstract: We present magnetic flux relaxation measurements which show that the flux creep behavior in the field and temperature range in which the lower critical field $Hc1$ is quenched to zero differs from that of the mixed state region above the mean field previous $Hc1(T)$ line. This is taken as evidence for the presence of magnetic excitations that cause the Meissner state to break down below the mean field $T_C$ at previous $H=0$.
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Pérez-Morelo, D. J., E. Osquiguil, A. B. Kolton, G. Nieva, I. W. Jung, D. López, and H. Pastoriza. "Thermodynamic evidence for the Bose glass transition in twinned YBa2Cu3O7-δ crystals." Physical Review B 92, no. 2 (2015): 020510.
Abstract: We used a micromechanical torsional oscillator to measure the magnetic response of a twinned YBa2Cu3O7−δ single crystal disk near the Bose glass transition. We observe an anomaly in the temperature dependence of the magnetization consistent with the appearance of a magnetic shielding perpendicular to the correlated pinning of the twin boundaries. This effect is related to the thermodynamic transition from the vortex liquid phase to a Bose glass state.
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Rumi, G., L. J. Albornoz, P. Pedrazzini, M. I. Dolz, H. Pastoriza, C. J. van der Beek, M. Konczykowski, and Y. Fasano. "Entropy jump at the first-order vortex phase transition in Bi2Sr2CaCu2O8+δ with columnar defects." Materials Today: Proceedings 14 (2019): 30–33.
Abstract: We study the entropy jump associated with the first-order vortex melting transition (FOT) in Bi2Sr2CaCu2O8+δ crystals by means of Hall probe magnetometry. The samples present a diluted distribution of columnar defects (CD) introduced by irradiation with Xe ions. The FOT is detected in ac transmittivity measurements as a paramagnetic peak, the height of which is proportional to the enthalpy difference entailed by the transition. By applying the Clausius-Clapeyron relation, we quantify the evolution of the entropy jump Δs as a function of the FOT temperature, TFOT, in both pristine crystals and crystals with CD. On increasing the density of CD, Δs decreases monotonically with respect to values found in pristine samples. The Δs versus TFOT dependence in the case of pristine samples follows reasonably well the theoretical prediction of dominant electromagnetic coupling for a model neglecting the effect of disorder. The data for samples with a diluted distribution of CD are not properly described by such a theoretical model.
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Safar, H., H. Pastoriza, F. de la Cruz, D. J. Bishop, L. F. Schneemeyer, and J. V. Waszczak. "Bulk phase transition in YBa$2$Cu$3$O7-δ single crystals." Phys. Rev. B 43, no. 16 (1991): 13610–13613.
Abstract: Precise magnetization measurements of YBa$2$Cu$3$O7-δ single crystals have found evidence for a bulk phase transition a few degrees below the superconducting critical temperature. The phase transition is indicated by a sudden drop of the lower critical field , $H_C1(T)$, separating a full coherent state at low fields and temperatures, the Meissner state, from a region at higher temperatures where magnetic excitations are induced at $H=0$.
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Safar, H., H. Pastoriza, J. Guimpel, F. de la Cruz, D. J. Bishop, L. F. Schneemeyer, and J. V. Waszczak. "Breakdown of the Meissner state in YBa$2$Cu$3$O7-?." In Transport properties of superconductors, edited by R. Nicolsky, 140. Progress in High Temperature Superconductivity 25. Singapore: World Scientific, 1990.
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Salazar Alarcón, L. and Martínez, E. D. and Rodríguez, L. M. and Pastoriza, H. "Topographical and Physicochemical Contrast in Photopatterned SU-8 Films for Microfabrication of Multilayer Structures." Advances in Materials Science and Engineering 2016 (2016): 5278102.
Abstract: During SU-8 standard photolithography process, a patterned topography is formed with a characteristic height profile produced by the different shrinkage of the UV exposed and masked regions. We study the change of wettability, film solubility, and topographic modifications on SU-8 films of different thicknesses and show its relevance in the formation of spinning-flow arrays on top layers made from positive photoresists. Also, considerable contrast in film solubility and surface energy as observed from contact angle measurements is produced. Interface diffusion of the photoresists was also observed and followed by Rutherford Back Scattering. We discuss the derivations of the mentioned effects concerning the limitations to multilayered microfabrication processes and possibilities to take advantage of the surface profiles obtained.
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Shalóm, D. E., and H. Pastoriza. "Vortex motion rectification in Josephson junction arrays with a ratchet potential." Phys. Rev. Lett. 94, no. 17 (2005): 177001.
Abstract: By means of electrical transport measurements we have studied the rectified motion of vortices in ratchet potentials engineered on over-damped Josephson junction arrays. The rectified voltage as a function of the vortex density shows a maximum efficiency close a matching condition to the period of the ratchet potential indicating a collective vortex motion. Vortex current reversals where detected varying the driving force and vortex density revealing the influence of vortex-vortex interaction in the ratchet effect.
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Shalóm, D. E., and H. Pastoriza. "Experimental Method to Measure Anisotropic Transport in 2D Superconductors." Journal of Low Temperature Physics 135 (2004): 153–156.
Abstract: A two-coil kinetic inductance technique for measuring anisotropic response in two-dimensional (2D) superconductors is presented. Serpentine-shaped coils are lithographically patterned directly on top of the sample, separated by isolation layers. The drive and receive coils are positioned in a way that enhances signal from longitudinal currents and reduces transversal ones, maximizing the ratio. Anisotropic transport can be directly measured with this technique, even when anisotropy is induced by the transport current.
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