Ale Crivillero, M. V., M. L. Amigó, D. G. Franco, A. Badía-Majós, J. Guimpel, and G. Nieva. "In Plane Vortex Dynamic Anisotropy in the Iron Deficient Fe_{1-y}Se Superconductor." Journal of Low Temperature Physics 179, no. 1-2 (2015): 9–14.
Abstract: We present electrical transport measurements in the superconducting dissipative state of crystalline iron deficient Fe 1−y Se samples. These iron deficient samples were synthesized using NaCl/KCl flux and are characterized by the presence of correlated defects. The dissipation in electrical transport experiments, when the driving current is perpendicular or parallel to the crystal planes, depends strongly on the direction of the applied magnetic field , ( H=12 T), within the sample plane. There is a dissipation modulation each 60∘ due to the presence of the correlated defects. We correlate these angular dependent features with the variation of the critical currents ( Jc ) changing the direction of H confined in the crystals planes. Jc was measured from magnetization loops at fixed temperatures and angles of H always within the basal planes.
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Aragón Sánchez, J., R. Cortés Maldonado, M. I. Dolz, N. R. CejasBolecek, C. J. van der Beek, M. Konczykowski, and Y. Fasano. "Direct visualization of local interaction forces in Bi2Sr2CaCu2O8+δ vortex matter." Materials Today: Proceedings 14 (2019): 34–37.
Abstract: We study the local vortex-vortex interaction force fi of the structure frozen during a field-cooling process in an electron-irradiated Bi2Sr2CaCu2O8+δ sample. We compute this magnitude from snapshots of the vortex structure obtained via magnetic decoration experiments at various fields H in the same sample. Since the observed structures correspond to the equilibrium ones frozen at T∼Tirr(H)[1], at this temperature the local modulus of fi roughly equals the local pinning force at the decorated surface of the sample. We estimate the most probable local pinning force from the mode value of the fi(r)distribution, fpm. We found that fpm grows algebraically with H and in electron-irradiated samples is 50-20% smaller than for samples with columnar defects.
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Cejas Bolecek, N. R., M. I. Dolz, A. Kolton, H. Pastoriza, C. Jvander Beek, M. Konczykowski, M. Menghini, G. Nieva, and Y. Fasano. "Geometrical Confinement Effects in Layered Mesoscopic Vortex Matter." Journal of Low Temperature Physics 179, no. 1-2 (2015): 35–41.
Abstract: We study the geometrical confinement effect in Bi 2 Sr 2 CaCu 2 O 8+δ mesoscopic vortex matter with edge-to-surface ratio of 7–12 %. Samples have in-plane square and circular edges, 30 μ m widths, and ∼ 2 μ m thickness. Direct vortex imaging reveals the compact planes of the structure align with the sample edge by introducing topological defects. The defect density is larger for circular than for square edges. Molecular dynamics simulations suggest that this density is not an out-of-equilibrium property but rather determined by the geometrical confinement.
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D'Anna, G., and Andr. "Flux-line response in 2H-NbSe2 investigated by means of the vibrating superconductor method." Physica C: Superconductivity and its applications 218, no. 1-2 (1993): 238–244.
Abstract: We measure transverse AC losses in the low- and high-amplitude regime of 2H-NbSe2 single crystals using vibrating superconductor methods. The measurements are sensitive to small deviations of the critical state. The data constitute evidence for a peak effect of the critical current as a function of the temperature in this compound. We construct in the H-T phase diagram the “peak-effect” line which is supposed to mark an abrupt cross-over in the vortex-pinning regime.
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Decca, R., E. Osquiguil, F. de la Cruz, C. D'Ovidio, M. T. Malachevski, and D. Esparza. "Non linear temperature dependence of the resistivity of LaSrCuO: Effects of Sr content." Solid State Communications 69, no. 4 (1989): 355–357.
Abstract: The linear temperature dependence of the electrical resistivity has been taken to be one of the characteristic features of the ceramic superconductors. Measurements of the electrical resistance of the LaSrCuO system in a wide temperature range show that the previous statement is only an approximation valid for some values of the Sr concentration.
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Decca, R. S., H. D. Drew, B. Maiorov, J. Guimpel, and E. J. Osquiguil. "Inducing superconductivity at a nanoscale: Photodoping with a near- field scanning optical microscope." Journal of Microscopy 194, no. 2-3 (1999): 407–411.
Abstract: The local modification of an insulating GdBa2Cu3O6.5 thin film, made superconducting by illumination with a near-field scanning optical microscope (NSOM), is reported. A 100-nm aperture NSOM probe acts as a sub- wavelength light source of wavelength ?(exc)=480-650 nm, locally generating photocarriers in an otherwise insulating GdBa2-Cu3O6.5 thin film. Of the photogenerated electron-hole pairs, electrons are trapped in the crystallographic lattice, defining an electrostatic confining potential to enable the holes to move. Reflectance measurements at ? = 1.55 ?m at room temperature show that photocarriers can be induced and constrained to move on a ?? 200 nm scale for all investigated ?(exc). Photogenerated wires present a superconducting critical temperature T(c) = 12 K with a critical current density J(c) = 104 A cm-2. Exploiting the flexibility provided by photodoping through a NSOM probe, a junction was written by photodoping a wire with a narrow (? 50 nm) under-illuminated gap. The strong magnetic field modulation of the critical current provides a clear signature of the existence of a Josephson effect in the junction.
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Decca, R. S., H. D. Drew, E. Osquiguil, B. Maiorov, and J. Guimpel. "Anomalous proximity effect in underdoped YBa2Cu3O6+x Josephson junctions." Physical Review Letters 85, no. 17 (2000): 3708–3711.
Abstract: Experiments were carried out to probe the underdoped insulating material by the Josephson effect. Junctions were fabricated by exploiting the capability of locally photodoping insulating RBa2Cu3O6+x (R = rare earth) material. The existence of an anomalously large proximity effect was confirmed. The critical current of the junctions was consisted with the conventional Josephson relationship.
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Dhalle, M., W. Boon, E. Osquiguil, C. Van Haesendonck, Y. Bruynseraede, J. Kwarciak, and O. Van Der Biest. "Correlation between critical current and resistivity in YBa2Cu3O7." Physica C: Superconductivity and its applications 185-189, no. PART 4 (1991): 2447–2448.
Abstract: Critical current versus temperature measurements were carried out in ceramic YBa2Cu3O7 samples. The samples were all prepared using the same sintering procedure, but starting from powders obtained by different wet and dry methods. All samples showed a linear Jc vs. T behaviour, typical of Josephson weak-link coupling, with a slope that depends on the preparation method. Using the Ambegaokar-Baratoff relation for Jc, the difference in slopes can be attributed to a change in the characteristic value of the junction resistance. This value turns out to be clearly correlated with the resistivity in the normal state.
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Dolz, M. I., P. Pedrazzini, H. Pastoriza, M. Konczykowski, and Y. Fasano. "Effect of Quenched Disorder in the Entropy-Jump at the First-Order Vortex Phase Transition of Bi{2}Sr{2}CaCu{2}O{8 + \delta }." Journal of Low Temperature Physics 179, no. 1-2 (2015): 28–34.
Abstract: We study the effect of quenched disorder in the thermodynamic magnitudes entailed in the first-order vortex phase transition of the extremely layered Bi 2 Sr 2 CaCu 2 O 8+δ compound. We track the temperature-evolution of the enthalpy and the entropy jump at the vortex solidification transition by means of AC local magnetic measurements. Quenched disorder is introduced to the pristine samples by means of heavy-ion irradiation with Pb and Xe producing a random columnar-track pins distribution with different densities (matching field BΦ ). In contrast with previous magneto-optical reports, we find that the first-order phase transition persists for samples with BΦ up to 100 Gauss. For very low densities of quenched disorder (pristine samples), the evolution of the thermodynamic properties can be satisfactorily explained considering a negligible effect of pinning and only electromagnetic coupling between pancake vortices lying in adjacent CuO planes. This description is not satisfactory on increasing magnitude of quenched disorder.
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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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