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Journal Articles

Direct imaging of vortex polygons and vortex shells in mesoscopic squares of a weak pinning superconducting thin film

Kokubo, Nobuhito*; Okayasu, Satoru; Nojima, Tsutomu*; Tamochi, Hirotaka*; Shinozaki, Bunju*

Journal of the Physical Society of Japan, 83(8), p.083704_1 - 083704_5, 2014/08

 Times Cited Count:14 Percentile:26.59(Physics, Multidisciplinary)

Journal Articles

Scanning SQUID microscope study of vortex polygons and shells in weak-pinning disks of an amorphous superconducting film

Kokubo, Nobuhito*; Okayasu, Satoru; Kanda, Akinobu*; Shinozaki, Bunju*

Physical Review B, 82(1), p.014501_1 - 014501_7, 2010/07

 Times Cited Count:26 Percentile:24.76(Materials Science, Multidisciplinary)

Direct observation of vortices by the scanning SQUID microscopy was made on large mesoscopic disks of an amorphous MoGe thin film. Owing to the weak pinning nature of the amorphous film, vortices are able to form geometry induced (quasi-)symmetric configurations of polygons and concentric shells in the large disks. Systematic measurements made on selected disks allow us to trace not only how the vortex pattern evolves with magnetic field, but also how the vortex polygons change in size and rotate with respect to the disk center. The results are in good agreement with theoretical considerations for mesoscopic disks with sufficiently large diameter. A series of vortex images obtained in a disk with a pinning site reveals a unique line of symmetry in vortex configurations, resulting in modifications of the shell filling rule and the magic number.

Journal Articles

Shell structures of vortices in superconducting disks of an amorphous MoGe film

Kokubo, Nobuhito*; Okayasu, Satoru; Shinozaki, Bunju*

Physica C, 468(15-20), p.1316 - 1318, 2008/09

 Times Cited Count:6 Percentile:66.83(Physics, Applied)

We have investigated spatial distributions of vortices induced in small superconducting disks of amorphous MoGe. Scanning SQUID microcopy allows us to observe directly magnetic distributions near the surface of the disks. Results on disks with diameter 0.05 mm demonstrate that quasi-symmetric distributions imposed by the circle geometry appear for vorticity up to 5. Meanwhile, for vorticity more than 6, vortices form an unique shell structure, in which one vortex is located in the center and others form a circle around. The critical vorticity for this structural transition is consistent with results on Nb disks imaged by the magnetic decoration experiments.

Oral presentation

Distributions of superconducting vortices confined in mesoscopic superconductors

Kokubo, Nobuhito*; Okayasu, Satoru; Tamochi, Hirotaka*; Shinozaki, Bunju*

no journal, , 

In a mesoscopic superconductor, characteristic configurations of quantum vortices, such as polybonal structures or shell structures, can be observed. We have been investigating the votices configurations in amorphous MoGe mesoscopic diskform superconductors using a scanning SQUID microscope. In this study, we expand our research objects to 80$$mu$$m $$times$$ 80$$mu$$m square-shaped superconductors. The vortices configurations appear with the different symmetries from the circular case.

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