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Critical current densities and vortex dynamics in Ba(Fe$$_{1-x}$$Co$$_{x}$$)$$_{2}$$As$$_{2}$$ single crystals

Ba(Fe$$_{1-x}$$Co$$_{x}$$)$$_{2}$$As$$_{2}$$単結晶の臨界電流密度と磁束ダイナミクス

為ヶ井 強*; 田縁 俊光*; 土屋 雄司*; 仲島 康行*; 岡安 悟  ; 笹瀬 雅人*

Tamegai, Tsuyoshi*; Taen, Toshihiro*; Tsuchiya, Yuji*; Nakajima, Yasuyuki*; Okayasu, Satoru; Sasase, Masato*

高品質の単結晶Ba(Fe$$_{1-x}$$Co$$_{x}$$)$$_{2}$$As$$_{2}$$の超伝導特性を幅広いキャリアドープ範囲に渡って調べた。適正ドープ単結晶(Tc$$sim$$24K)の臨界電流密度$$J$$$$_{rm c}$$は5テスラ10K以下で10$$^{5}$$A/cm$$^{2}$$を超える値を示し、フィッシュテール効果が現れた。結晶中には多くの不純物を含んでいるにもかかわらず、結晶中を均一の超伝導電流が流れていることが磁気光学イメージ法で明らかになった。重イオン照射試料では円柱状欠陥による$$J$$$$_{rm c}$$の増大を示し、低温では未照射試料の5倍にも達し、ゼロ磁場2Kで6$$times$$10$$^{6}$$A/cm$$^{2}$$の値を示した。重イオン照射試料ではJcの増大に伴って磁束クリープ緩和率が減少した。

Superconducting properties are evaluated for high-quality single crystals of Ba(Fe$$_{1-x}$$Co$$_{x}$$)$$_{2}$$As$$_{2}$$ in a wide range of doping levels. The critical current density, $$J$$$$_{rm c}$$, in an optimally-doped crystal (Tc $$sim$$ 24 K) shows a fishtail effect with its value over 10$$^{5}$$ A/cm$$^{2}$$ even at 5 T below 10 K. Magneto-optical imaging has clarified rather homogeneous supercurrent flow in the crystal, in spite of a large amount of impurities. In the heavy-ion irradiated sample, the presence of columnar defects are confirmed and $$J$$$$_{rm c}$$ has been enhanced by a factor of five at low temperatures, reaching 6 $$times$$ 10$$^{6}$$ A/cm$$^{2}$$ at 2 K under zero field. Flux creep rate in the heavy-ion irradiated sample has been reduced in accordance with the enhancement of $$J$$$$_{rm c}$$.

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分野:Physics, Applied

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