Observation of symmetric patterns in the flux distribution of thin YBa2Cu3O7−x films

Abstract

We havc ~nvestigated the magnetic field distribut~on in epitaxial YBa,Cu,O,-, films on square SrTiO, and MgO substrates. Fn fields between 20 mT and IT a magnetooptic method was applied,complemcn~cd by a qcanntng micro Hall probe for the low field range. Thc flus ~sobsenped to penetrate Ln a rarher rceular way. displaying the fourfold svmmetn of our ramples The penetratxon starts preferent~ally from the sample edees. A qualltat~ve description of 1 h 1~ penetration process 1s sup~ested, whlch rcl!rs an the cumat ure oft he shield~ng cursent paths. 1.Tntaoduction ning micro Halt probe, which confirmed these results.Among the potential applications of high-T, superconductors thin epitaxial films of ~h e s e materials will certainly play a prominent role. For this purpose it is essential to have methods available which allow one to check the sample quality on a large scale, simultaneously being fast and conlacrlcss. Here we reporl on measurements with a magneto-optical technique which fulfills these requirements.We have used this method to study the penetration of magnetic flux and the resulting distribution in square YBa,Cu,O,-, The rneasuremcnts were performed in a n optical toploading cryostat down to temperatures of 2 K.

Crossover between fractal and nonfractal flux penetration in high-temperature superconducting thin films

“…[1][2][3][4][5][6][7][8][9] This behavior is in contrast with the smooth and well-defined flux penetration observed in single crystals 1,2,10-17 and in some thin films. 1,18,19 That the flux penetration in thin films is often more fractal-like than in single crystals is rather surprising since the stability of the flux front should increase for decreasing thickness, and hence be very stable in the thin-film case.…”

Influence of microscopic defects in type-II superconducting thin films on the magnetic flux penetration

“…In a perpendicular external magnetic field flux enters a quadratic or rectangular type-II superconducting thin film preferentially at the edges in the form of a convex flux front, but not from the corners. 8,18,19 On the right and the left of the sample in Fig. 2 the flux distribution is locally disturbed by natural and artificial defects.…”

Dynamics of the dendritic flux instability in YBa 2 Cu 3 O 7 − δ films

“…-Due to the high velocity of the flux dendrites in thin films a temporal resolution in the sub-nanosecond regime is required to register the development of flux avalanches with sufficient accuracy. We have used a magneto-optic technique, with a Bi-doped Yttrium Iron Garnet (YIG) film on Gadolinium Gallium Garnet as the sensor layer [14], which was mounted on top of the superconductor [15]. The spatial resolution was on the order of a few µm.…”