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The field-amplitude and frequency dependent complex ac susceptibility of a well sintered YBa2Cu3O7−δ disk has been measured at 77K, which shows that its intra- and intergranular critical-current densities are determined by the collective flux creep inside the grains and the maximum Josephson currents across the grain boundaries, respectively. While the former is widely recognized, the latter contrasts to a popular belief of a mechanism of Josephson-vortex pinning and creep.
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Chen et al. (2006) studied this question.
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