Department of Applied Physics, University of Tokyo, Japan
In this talk, flux penetrations and thermomagnetic instabilities in three-dimensional nanostructured superconductors visualized using magneto-optical imaging are presented. In two-layer superconducting shifted strip arrays (S-SSA), where strips in the neighboring layers are shifted by half a period, we find a novel flux avalanche traversing strips that are not electrically connected to each other. In a series of experiments on S-SSA, we clarify the evolution of flux avalanches by increasing the layer number and introducing various types of asymmetries. We also studied flux penetrations into two layers of superconducting multiple-square washers (S-MSW) that are stacked by shifting neighboring layers as in S-SSA. Contrary to our expectations, we do not observe large scale flux avalanches in S-MSW. However, when a part of the washer is cut using FIB, we immediately recovered a situation similar to S-SSA. There appear flux avalanches and characteristic flux penetrations at the inner corners of washers. These complicated flux penetrations into disconnected S-MSW are discussed based on thermomagnetic instabilities and the current crowding effect.
Prof. Tsuyoshi Tamegai obtained Ph. D degree fromthe University of Tokyo in 1987. He got a position as a research associate at Institute for Solid State Physics, University of Tokyo in 1986. He joined IBM T. J. Watson research center as a guest researcher from 1990 to 1991 and from 1992 to 1993. He has been an associate professor at Department of Applied Physics, University of Tokyo since 1993. His main research area is on electromagnetic properties of superconductors including the pinning mechanism of vortices. Prof.Tamegai has applied local magnetometry to various kinds of superconductors such as cuprate and iron-based superconductors. He hasstudied the effect of swift-particle irradiation on iron-based superconductors and the magnetic properties of two- and three-dimensional nanostructured superconductors.