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(Reference retrieved automatically from SciELO through information on FAPESP grant and its corresponding number as mentioned in the publication by the authors.)

Controversial features of granular superconductors studied through the magnetic properties of 2d-Josephson junction arrays

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W. Maluf ; F. M. Araujo-Moreira
Total Authors: 2
Document type: Journal article
Source: Brazilian Journal of Physics; v. 32, n. 3, p. 717-730, Set. 2002.

We have shown that the Paramagnetic Meissner Effect (PME) is directly associated with pinning, and not necessarily related to the presence of pi-junctions. Through the study of the magnetic properties of two-dimensional Josephson junction arrays (2D-JJA) in the present work we show that, among the systems exhibiting PME, only those with suffciently low dissipation and high capacitance will show dynamics reentrance. The concept of a critical state and its use in the interpretation of AC magnetization data in terms of a critical current density were introduced to derive the magnetic properties of hard type-II superconductors. In the critical state model proposed by Bean, flux lines penetrate into the sample and, due to the presence of disorder they give rise to a steady flux gradient. Here we show that in 2D-JJA this typical picture is valid only in short-range distances. For long-range distances, the picture of uniform flux fronts, as described by a critical state model, breaks down and the penetration of the magnetic field takes place through the growth of magnetic dendrites. De Gennes originally compared the slope of a pile of vortices to a sand-pile, with the slope being proportional to the local magnitude of the critical current. Dynamical properties of the sand-pile problem have attracted new attention since it consists of a marginally stable system displaying self-organized criticality (SOC). In this case, when a superconductor is in the Bean critical state, the addition of vortices occurs by increasing the external magnetic field. This procedure is analogous to the introduction of new grains to a sand-pile and is expected to produce an avalanche of grains of sand (or, equivalently, vortices) of all sizes to maintain a constant gradient in the grain (or, magnetic ux) density. We show in this work strong evidences pointing out that, for some specific conditions, magnetic field penetrates 2D-JJA in ux avalanches. (AU)

FAPESP's process: 98/12809-7 - Magnetic properties of Type Nb–AlOx–Nb 2D-Josephson junction arrays
Grantee:Fernando Manuel Araújo Moreira
Support type: Regular Research Grants
FAPESP's process: 98/12593-4 - Study of the magnetic properties of Type Nb–AlOx–Nb 2D-Josephson junction arrays
Grantee:Walter Maluf Junior
Support type: Scholarships in Brazil - Master