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Vortex avalanches in superconductors
 

Review: Experiments in vortex avalanches

E. Altshuler and T. H. Johansen
Reviews of Modern Physics, 76, 471 (2004); cond-mat/0402097; PDF (1Mb)

Avalanche dynamics is found in many phenomena spanning from earthquakes to the evolution of species. It can be also found in vortex matter when a type II superconductor is externally driven, for example, by increasing the magnetic field. Vortex avalanches associated with thermal instabilities can be an undesirable effect for applications, but "dynamically driven" avalanches emerging from the competition between intervortex interactions and quenched disorder constitute an interesting scenario to test theoretical ideas related with non-equilibrium dynamics. However, differently from the equilibrium phases of vortex matter in type II superconductors, the study of the corresponding dynamical phases - in which avalanches can play a role - is still in its infancy. In this paper we critically review relevant experiments performed in the last decade or so, emphasizing the ability of different experimental techniques to establish the nature and statistical properties of the observed avalanche behavior.

 


Vortex avalanches and self organized criticality in superconducting niobium

E. Altshuler et al.
Phys. Rev. B 2004 ; PDF

 

In 1993 Tang proposed [1] that vortex avalanches should produce a self organized critical state in superconductors, but conclusive evidence for this has heretofore been lacking. In the present paper, we report extensive micro-Hall probe data from the vortex dynamics in superconducting niobium, where a broad distribution of avalanche sizes scaling as a power-law for more than two decades is found. The measurements are combined with magneto-optical imaging, and show that over a widely varying magnetic landscape the scaling behaviour does not change, hence establishing that the dynamics of superconducting vortices is a SOC phenomenon.

 



 

2 types of jumps

flux jump in a superconducting film

Theory of flux jump size; Small and big jumps in MgB2

D. V. Shantsev et al.
Phys.Rev.B-2005   PDF,

A. V. Bobyl et al.
Physica C 2004 PDF

Experiment

Magneto-optical imaging was used to visualize the flux penetration in MgB2 films subjected to a slowly varying perpendicular field. Below 10 K, flux jumps with typical size 10-20 microns and regular shape are found to occur at random locations along the flux front. The total number of vortices participating in one jump is varying between 50 and 10000. Simultaneously, big dendritic jumps with dimensions comparable to the sample size (10^6-10^8 vortices) are also found in this temperature range. We believe that both types of jumps result from thermo-magnetic instability.

On the Figure:
The first jump was detected at 4 mT and was as small as 20 vortices. At larger fields more jumps were found with average size gradually increasing to 10000 vortices. At 15 mT the first dendritic jump occured which consisted of millions of vortices.

Theory

Size of flux jumps in superconducting films is calculated assuming their thermal origin. The model is based on the adiabatic approach and takes into account nonlocal electrodynamics in thin superconductors. Flux and temperature distributions in the final state after a jump (adiabatic critical state) are found. The threshold field for thermal avalanches is predicted to be much smaller than that for thick superconductors. All these results as well as field dependence of the jump size are in agreement with experiment on MgB2 films.

 


 

Collapse of the critical state in superconducting niobium: Uniform flux jumps

R. Prozorov et al.
Phys. Rev. B 74, 220511(R) (2006)
PDF

 



Video from ameslab.gov
Giant abrupt changes in the magnetic flux distribution in Nb foils were studied by using magneto-optical visualization, thermal and magnetic measurements. Uniform flux jumps and sometimes almost total catastrophic collapse of the critical state are reported. Results are discussed in terms of thermomagnetic instability mechanism with different heat removal channels.

More videos of jumpy flux penetration in Nb

 

 

 


 

Real-time magneto-optical imaging of vortex avalanches in NbSe2

M. Baziljevich et al.
Adv. Sci. Tech. 38, 377 (2003), PDF