Is the bean critical state self-organised?

Barford, William; Beere, W.H.; Steer, M. J.

doi:10.1016/0921-4526(94)91407-9

Cited by 2 publications

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“…It is this type of behaviour that has been named the self-organized criticality. Such magnetic flux avalanches have also been observed experimentally (see, e.g., [33,34,[40][41][42][43]).…”

Section: Introductionmentioning

confidence: 60%

“…After the discovery of self-organized criticality [31,32], the hypothesis of self-organization of the critical state in hightemperature superconductors has also been elaborated [33,34]. According to the results of [35], if the characteristic size of an elementary Josephson loop formed by adjacent grains a much exceeds the effective penetration depth λ eff :…”

Section: Introductionmentioning

confidence: 99%

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Voltage fluctuations in granular superconductors in the perpendicular configuration

Gerashchenko

2003

Supercond. Sci. Technol.

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The spectral density of voltage fluctuations in granular YBa2Cu3O7−δ superconductors in the perpendicular configuration has been studied in the flux flow mode. It has been found that, in this case, the 1/f-voltage noise observed depends weakly on temperature and is associated with motion of a magnetic flux in the superconductor. A comparison of the data obtained with the results of previous measurements in parallel configuration has shown that voltage noise is produced by a single common source, which is presumably associated with self-organization of the critical state in granular superconductors.

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“…It is this type of behaviour that has been named the self-organized criticality. Such magnetic flux avalanches have also been observed experimentally (see, e.g., [33,34,[40][41][42][43]).…”

Section: Introductionmentioning

confidence: 60%

Section: Introductionmentioning

confidence: 99%

Voltage fluctuations in granular superconductors in the perpendicular configuration

Gerashchenko

2003

Supercond. Sci. Technol.

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Evidence for self-organized criticality in the Bean critical state in superconductors

Aegerter

1998

Phys. Rev. E

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The time dependence of the magnetization of a type-II superconductor in the Bean critical state is studied. It is found that evolution occurs in the form of bursts, consistent with a model exhibiting self-organized criticality. The distribution of step sizes follows a power law with an exponent of ␣Ӎ 2. At high temperatures the distribution is Gaussian-like, as would be expected in an equilibrium situation. This may allow the experimental study of the occurrence of criticality. ͓S1063-651X͑98͒03508-9͔ PACS number͑s͒: 64.60. Lx, 74.60.Ge, 05.40.ϩj, 87.10.ϩe In a type-II superconductor an applied magnetic field may penetrate into the bulk of the superconducting sample. This happens in the form of quantized lines of magnetic flux. In equilibrium, these flux lines ͑or vortices͒ form a regular hexagonal lattice. Defects in the crystal structure, suppressing the superconductivity, may be favoring the position of a vortex line, effectively pinning it. Thus when the superconductor is driven out of the equilibrium situation it is these pinning sites that determine its behavior ͓1͔. This can be achieved, for instance, by applying the field in the superconducting state, such that penetrating vortices get pinned near the surface. These pinned vortices then repel other entering vortices, leading to an extremal dynamics of the whole system, where the most weakly pinned flux lines depin in order to give way to the pressure exerted by the penetrating flux lines. As is the case in a sandpile, this will eventually lead to a situation with a constant gradient ͑here of magnetic field͒ over the boundary. Such a situation has already been described by Bean some 30 years ago ͓2͔. Recently it has been noted that this state may be an example of self-organized criticality ͑SOC͒ ͓3͔ and thus be governed by power-law distributions in its dynamics ͓4,5͔.SOC has been invoked to explain a host of natural phenomena, ranging from earthquakes ͓6͔ to biological macroevolution ͓7-9͔, that take place far from thermodynamic equilibrium. In the case of earthquakes this is borne out by the Gutenberg-Richter law, describing a power-law distribution in the strength of earthquakes. This is taken as a sign of a critical state, where there are fluctuations on all scales as given by a power-law distribution. In macroevolution, the discovery of punctuated equilibrium in the fossil record by Gould and Eldredge ͓10͔ has led to speculations that similar to the Earth's crust, the biosphere could be in a critical state leading to the observed power-law behavior in the extinction pattern. In the original proposition of SOC the picture of a sandpile was invoked to convey a physical picture of the computer model ͓3͔. Consider a table onto which we drop sand grains at random. After a certain growth period, there will be a sandpile of definite slope that no longer changes with time. In that case the sandpile is in a critical state, where the slope is kept constant by occasional bursts of sandslides ͑avalanches͒, whose size distribution takes the form of a power law....

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Is the bean critical state self-organised?

Cited by 2 publications

References 4 publications

Voltage fluctuations in granular superconductors in the perpendicular configuration

Voltage fluctuations in granular superconductors in the perpendicular configuration

Evidence for self-organized criticality in the Bean critical state in superconductors

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