Aragón Sánchez, J., R. Cortés Maldonado, N. R. Cejas Bolecek, G. Rumi, P. Pedrazzini, M. I. Dolz, G. Nieva, C. J. van der Beek, M. Konczykowski, C. D. Dewhurst et al. "Unveiling the vortex glass phase in the surface and volume of a type-II superconductor." Communications Physics 2, no. 1 (2019): 143.
Abstract: Order-disorder transitions between glassy phases are common in nature and yet a comprehensive survey on the entailed structural changes is challenging since the constituents are in the micro-scale. Vortex matter in type-II superconductors is a model system where some of these experimental challenges can be tackled. Samples with point disorder present a glassy transition on increasing the density of vortices. A glassy yet quasi-crystalline phase, the Bragg glass, nucleates at low densities. The vortex glass stable at high densities is expected to be disordered, however its detailed structural properties remained experimentally elusive. Here we show that the vortex glass has large crystallites with in-plane positional displacements growing algebraically and short-range orientational order. Furthermore, the vortex glass has a finite and almost constant correlation length along the direction of vortices, in sharp contrast with strong entanglement. These results are important for the understanding of disorder-driven phase transitions in glassy condensed matter.
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Cejas Bolecek, N. R., A. B. Kolton, M. Konczykowski, H. Pastoriza, D. Dominguez, and Y. Fasano. "Vortex matter freezing in Bi2Sr2CaCu28 samples with a very dense distribution of columnar defects." Physical Review B 93, no. 5 (2016): 054505.
Abstract: We show that the dynamical freezing of vortex structures nucleated at diluted densities in Bi2Sr2CaCu2O8 samples with a dense distribution of columnar defects, B∼10−2BΦ with BΦ=5kG, results in configurations with liquidlike correlations. We propose a freezing model considering a relaxation dynamics dominated by double-kink excitations driven by the local stresses obtained directly from experimental images. With this model we estimate the relaxation barrier and the freezing temperature. We argue that the low-field frozen vortex structures nucleated in a dense distribution of columnar defects thus correspond to an out-of-equilibrium nonentangled liquid with strongly reduced mobility rather than to a snapshot of a metastable state with divergent activation barriers as, for instance, expected for the Bose-glass phase at equilibrium.
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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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Demirdiş, S., C. J. van der Beek, Y. Fasano, N. R. Cejas Bolecek, H. Pastoriza, D. Colson, and F. Rullier-Albenque. "Strong pinning and vortex energy distributions in single-crystalline Ba(Fe{1−x}Co{x}){2}As{2}." Physical Review B 84, no. 9 (2011): 094517.
Abstract: The interrelation between heterogeneity and flux pinning is studied in Ba(Fe1−xCox )2As2 single crystals with widely varying Co content x.Magnetic Bitter decoration of the superconducting vortex ensemble in crystals with x = 0.075 and x = 0.1 reveals highly disordered vortex structures. The width of the Meissner belt bserved at the edges of the crystals, and above the surface steps formed by leaving, as well as the width of the intervortex distance distribution, indicate that the observed vortex ensemble is established at a temperature just below the critical temperature Tc. The vortex interaction energy and pinning force distributions extracted from the images strongly suggest that the vortex lattice disorder is attributable to strong pinning due to spatial fluctuations of Tc and of the superfluid density. Correlating the results with the critical current density ields a typical length scale of the relevant disorder of 40–60 nm.
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Facio, J. I., D. Betancourth, N. R. Cejas Bolecek, G. A. Jorge, P. Pedrazzini, V. F. Correa, P. S. Cornaglia, V. Vildosola, and García D.J. "Lattice specific heat for the RMIn5 (R=Gd, La,Y; M=Co, Rh) compounds: Non-magnetic contribution subtraction." Journal of Magnetism and Magnetic Materials 407 (2016): 406–4011.
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Puig, J., N. R. Cejas Bolecek, J. Aragón Sánchez, M. I. Dolz, M. Konczykowski, and Y. Fasano. "Bridge in micron-sized Bi2Sr2CaCu2O8 sample act as converging lens for vortices." Physica C: Superconductivity and its Applications 590 (2021): 1353948.
Abstract: We report on direct imaging of vortex matter nucleated in micron-sized BiSrCaCuO superconducting samples that incidentally present a bridge structure. We find that when nucleating vortices in a field-cooling condition the deck of the bridge acts as a converging lens for vortices. By means of Bitter decoration images allowing us to quantify the enhancement of vortex-vortex interaction energy per unit length in the deck of the bridge, we are able to estimate that the deck is thinner than m. We show that the structural properties of vortex matter nucleated in micron-sized thin samples are not significantly affected by sample-thickness variations of the order of half a micron, an important information for type-II superconductors-based mesoscopic technological devices.
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Rumi, G., J. Aragón Sánchez, F. Elías, R. Cortés Maldonado, J. Puig, N. R. Cejas Bolecek, G. Nieva, M. Konczykowski, Y. Fasano, and A. B. Kolton. "Hyperuniform vortex patterns at the surface of type-II superconductors." Physical Review Research 1, no. 3 (2019): 033057.
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van der Beek, C. J., S. Demirdis, M. Konczykowski, Y. Fasano, N. R. Cejas Bolecek, H. Pastoriza, D. Colson, and F. Rullier-Albenque. "Vortex pinning : a probe for nanoscale disorder in iron-based superconductors." Physica B 407, no. 11 (2012): 1746–1749.
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