Magneto-optic characterization of defects and study of flux avalanches in high-T-c superconductors down to nanosecond time resolution

Citation
Bu. Runge et al., Magneto-optic characterization of defects and study of flux avalanches in high-T-c superconductors down to nanosecond time resolution, LASER PHYS, 10(1), 2000, pp. 53-59
Citations number
19
Categorie Soggetti
Apllied Physucs/Condensed Matter/Materiales Science","Optics & Acoustics
Journal title
LASER PHYSICS
ISSN journal
1054660X → ACNP
Volume
10
Issue
1
Year of publication
2000
Pages
53 - 59
Database
ISI
SICI code
1054-660X(200001/02)10:1<53:MCODAS>2.0.ZU;2-4
Abstract
Optical methods offer an intrinsic high potential for experiments with exce llent spatial and in particular also temporal resolution. Using the Faraday effect we carried out magneto-optical investigations of high-T-c supercond uctor thin films in a polarization microscope. Small defects in the superco nducting material which possess a lower critical current density disturb th e homogeneous penetration of magnetic flux into a sample when an external m agnetic field is applied after zero field cooling. This is true even if the defects are below the sample surface or when the superconducting sample is covered by a thin layer of another material, e.g., gold, and can be used t o characterize samples with diameters up to 3 ". For studies of the dynamic s of magnetic flux in a superconducting sample, a pump-probe setup has been used. An instability which causes magnetic flux to enter the sample in den dritic form [1] is triggered by local heating with a focused ns or fs laser pulse. Part of the beam is separated by a beam splitter, passed through a variable delay line of suitable length and used for illumination of the sam ple. For YBa2Cu3O7-delta thin films a spreading velocity of (5 +/- 2) x 10( 4) m/s is found which is an order of magnitude higher than the velocity of sound. The total area of the dendritic structure formed is found to depend linearly on the change Delta B-ext of the external magnetic flux density ap plied before the trigger pulse. No dependence on the pulse duration has bee n observed, suggesting a purely thermal nature of the trigger process.