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Bolecek, N. R. C., M. I. Dolz, H. Pastoriza, M. Konczykowski, C. J. van der Beek, A. B. Kolton, and Y. Fasano. "Excess of topological defects induced by confinement in vortex nanocrystals." Physical Review B 96, no. 2 (2017): 024507.
Abstract: We directly image individual vortex positions in nanocrystals in order to unveil the structural property that contributes to the depletion of the entropy jump entailed at the first-order transition. On reducing the nanocrystal size, the density of topological defects increases near the edges over a characteristic length. Within this “healing-length†distance from the sample edge, vortex rows tend to bend, while towards the center of the sample, the positional order of the vortex structure is what is expected for the Bragg-glass phase. This suggests that the healing length may be a key quantity to model confinement effects in the first-order transition of extremely layered vortex nanocrystals.
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Dolz, M. I., N. R. C. Bolecek, J. Puig, H. Pastoriza, G. Nieva, J. Guimpel, C. J. van der Beek, M. Konczykowski, and Y. Fasano. "Enhancement of penetration field in vortex matter in mesoscopic superconductors due to Andreev bound states." Physical Review B 100, no. 6 (2019): 064508.
Abstract: We study the field for the penetration of a first vortex, HP, for vortex matter nucleated in micron-sized samples with edges aligned along the nodal and antinodal directions of the d-wave superconducting order parameter of Bi2Sr2CaCu2O8−δ. Here we present evidence that the HP for vortex matter nucleated in mesoscopic samples with edges parallel to the nodal direction is larger than for the antinodal case, ∼72% at low temperatures. This finding supports the theoretical proposal that surface Andreev bound states appearing in a sample with edges parallel to the nodal direction would produce an anomalous Meissner current that increases the Bean-Livingston barrier for vortex penetration.
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Sanchez, J. A., G. Rumi, R. C. Maldonado, N. R. C. Bolecek, J. Puig, P. Pedrazzini, G. Nieva, M. I. Dolz, M. Konczykowski, C. J. van der Beek et al. "Non-Gaussian tail in the force distribution: a hallmark of correlated disorder in the host media of elastic objects." Scientific Reports 10, no. 1 (2020): 19452.
Abstract: Inferring the nature of disorder in the media where elastic objects are nucleated is of crucial importance for many applications but remains a challenging basic-science problem. Here we propose a method to discern whether weak-point or strong-correlated disorder dominates based on characterizing the distribution of the interaction forces between objects mapped in large fields-of-view. We illustrate our proposal with the case-study system of vortex structures nucleated in type-II superconductors with different pinning landscapes. Interaction force distributions are computed from individual vortex positions imaged in thousands-vortices fields-of-view in a two-orders-of-magnitude-wide vortex-density range. Vortex structures nucleated in point-disordered media present Gaussian distributions of the interaction force components. In contrast, if the media have dilute and randomly-distributed correlated disorder, these distributions present non-Gaussian algebraically-decaying tails for large force magnitudes. We propose that detecting this deviation from the Gaussian behavior is a fingerprint of strong disorder, in our case originated from a dilute distribution of correlated pinning centers.
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