Schematic diagram of a MOI setup. A sample is mounted on a massive cold finger of a He-flow cryostat. Resistive coils are used as a source of external magnetic field. The light from a mercury lamp shines through a polarizer and is guided onto an indicator film, where it experiences Faraday rotation. The light is then reflected by a thin mirror and projected through an analyzer onto a CCD matrix of a computer-operated camera.
Dendritic flux avalanche observed in film by MOI. From Ref. 6.
Magneto-optical images of a NbN film at in increasing applied field, illustrating development of the dendritic flux avalanches. From Ref. 24.
MOI demonstrating irreproducibility of the flux distribution that results from the dendritic avalanches. (a) The three images were taken under identical experimental conditions. (b) Image obtained by superimposing the three images above. Repeatable parts of the flux front appear as gradations of white. From Ref. 25.
Magneto-optical images of dendritic flux avalanches in a NbN film taken at a) and b) .
One half of a superconductor strip on a substrate. The dark gray area is the flux-penetrated region (Ref. 31).
Dispersion relations for small and large , for and . From Ref. 31.
MOI of flux distribution in samples of different width at and magnetic field of . From Ref. 25.
Threshold magnetic field for onset of the dendritic instability in strips of different width. Experimental data (symbols) are in a good agreement with a fitted theoretical curve (solid curve), for . From Ref. 25.
Temperature dependence of the threshold magnetic field (from Ref. 25). Experimental data obtained for the wide sample (●) and for a wide Nb film (▲).13 The solid curves are theoretical fits. The dashed lines show the limiting temperature above which the instability vanishes.
Schematic plot illustrating the existence of two threshold fields for the dendritic instability, adapted from Ref. 24. The two main curves represent the dependence of the threshold field on the critical current density and a typical monotonic field dependence of . The intersection of the two curves defines the two thresholds and for the onset and vanishing of the instability.
Field dependence of the critical current density at measured using MOI in NbN thin film (Ref. 24).
Thermomagnetic instability diagram of NbN at (Ref. 24): the lower and upper threshold fields and , measured at different , limit the region where the dendritic avalanches were observed.
Instability onset field as a function of the critical current at in NbN thin film. From Ref. 24.
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