Estimation of Local Current Transport Properties in Thin Film Superconductor Based on Scanning Hall-probe Microscopy
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Estimation of Local Current Transport Properties in Thin Film Superconductor Based on Scanning Hall-probe Microscopy Kohei Higashikawa1, Kei Shiohara1, Masayoshi Inoue1, Takanobu Kiss1, Masateru Yoshizumi2 and Teruo Izumi2 1
Department of Electrical Engineering, Graduate School of ISEE, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan 2 Superconductivity Research Laboratory, International Superconductivity Technology Center, 1-10-13 Shinonome, Koto-ku, Tokyo 135-0062, Japan ABSTRACT To enhance a global critical current in a superconductor, it is indispensable to understand current limiting factors and their influence on such a critical current. From this point of view, we have investigated in-plane distribution of local critical current density and its electric field criterion in a thin-film superconductor by using scanning-Hall probe microscopy. In a remanent state, after the application of sufficiently high magnetic field to a sample, current flows at critical current density according to the critical state model. Such distribution of current density was estimated from that of measured magnetic field using the Biot-Savart law. Furthermore, the corresponding electric field criterion was evaluated from the relaxation of such remanent magnetic field by considering Faraday’s law. This means that we could estimate in-plane distribution of local critical current density as a function of electric field criterion in a nondestructive manner. This characterization method would be very helpful for finding current limiting factors in a thin-film superconductor and their influence on its global current density versus electric field properties which would usually be obtained by four-probe method. INTRODUCTION Characterization of local inhomogeneity in REBa2Cu3O7-δ (REBCO, RE: rare earth) coated conductors (CCs) will be a key technology for their further performance improvement and quality control necessary in the stage of industrial production. Magneto-optic imaging (MOI) [1, 2] is a powerful method for visualizing local inhomogeneity in CCs with a very good spatial resolution. TAPESTAR™ [3, 4] is a well-known method for estimating longitudinal distribution of critical current in CCs. On the other hand, we have been developing a characterization method based on scanning Hall-probe microscopy (SHPM) [5, 6]. The advantage of this method is the capability for estimating in-plane (two-dimensional) distribution of critical current density. This information would be very helpful for (1) quality control of an original conductor, (2) that of a narrower conductor slit from a wider one, (3) that of a multifilamentary conductor, (4) understanding of macroscopic current transport properties, and (5) investigating typical statistics correlated with the fabrication process.
However, we also found that the critical current obtained by SHPM was slightly different from that by the four-probe method. To understand the difference and to prove the validity of the method quantitatively, we discuss the electric field criterion fo
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