Huge compact flux avalanches in superconducting Nb thin films

• Published in: Physica. C, Superconductivity Superconductivity, 2004-09, Vol.411 (1), p.11-17
• Main Authors: Welling, M.S., Westerwaal, R.J., Lohstroh, W., Wijngaarden, R.J.
• Format: Article
• Language: English
• Subjects: Avalanche; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Exact sciences and technology; Flux jump; Low tc films; Magneto-optical imaging; Niobium; Physics; Properties of type I and type II superconductors; Superconducting films and low-dimensional structures; Superconductivity; Superconductor; Thin film; Vortex lattices ,flux pinning, flux creep
• ISSN: 0921-4534; 1873-2143
• DOI: 10.1016/j.physc.2004.06.011

Using a magneto-optical technique we perform a quantitative analysis of magnetic flux penetration in superconducting niobium thin films on A-plane ( 1 1 2 ¯ 0 ) sapphire substrates as a function of temperature (1.5 K ⩽ T ⩽ T c = 9.2 K). In these samples we observe huge compact avalanches (HCAs for brevity), very much like some snow-avalanches and unlike the rough dendritic flux penetration observed on R-plane ( 1 1 ¯ 0 2 ) sapphire. The behavior observed is consistent with the occurrence of thermo-magnetic avalanches as proposed by Aranson et al. [Phys. Rev. Lett. 87 (2001) 067003]. For increasing temperature, we find: (1) an increased branching of the HCA. (2) An increased applied field necessary for the first HCA to occur. (3) A decrease in the number of HCAs, accompanied by more ‘regular’ flux penetration (above 6.2 K avalanches are completely absent). (4) An increase of the total amount of flux as well as the area of the HCA.