パルス管冷凍機と可変磁場永久磁石によるBi-2212固有ジョセフソン接合の磁束フロー特性

抄録

A cryogen-free measurement system has been developed to examine the flux-flow phenomena in Bi₂Sr₂CaCu₂O_8+y (Bi-2212) intrinsic Josephson junctions. The system consists of a pulse-tube cryocooler and a variable-field permanent magnet. Flux-flow measurements were carried out at 44 K at which the Bi-2212 intrinsic Josephson junction exhibited 90% of the critical current at 4.2 K. Field direction could be set parallel to the superconducting CuO₂ layers of the intrinsic junctions accurately, free from pancake vortices. The current-voltage characteristics measured under magnetic fields up to 1 T revealed a broad velocity-matching step corresponding to the strongly coupled Josephson junction stack.