Successive Phase Transitions of a Hierarchical Nature in a YBa_2Cu_4O_8 Ceramic Superconductor

概要

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The superconductive ordering of a YBa_2Cu_4O_8 ceramic with a single phase and of homogeneous sub-micron size grains, is studied by systematic DC magnetic measurements under weak magnetic fields. Successive phase transitions of a hierarchical nature are identified to occur at two temperatures T_<C1>(≃ 80 K) and T_<C2>(≃ 37 K). The transition at T_<C1> is that from the normal into the intra-grain superconductive state. The transition at T_<C2> is that into the inter-grain superconductive state and results in an infinite superconductive network over the whole sample. Taking a possible Josephson junction type coupling into account, the second transition at T_<C2> is speculated to be a long range ordering among the superconductive grains and similar to that for a three-dimensional XY ferromagnet.
社団法人日本物理学会の論文
1994-09-15