2003 Fiscal Year Annual Research Report

乱れた超伝導体の極低温ボルテックス状態と量子ゆらぎ

Research Project

Project/Area Number	15340115
Research Institution	Tokyo Institute of Technology
Principal Investigator	大熊哲東京工業大学, 極低温物性研究センター, 助教授 (50194105)
Keywords	第2種超伝導体 / 混合状態 / ボルテックスグラス / 量子ゆらぎ / ノイズ / ゆらぎ / 交流インピーダンス / アモルファス膜
Research Abstract	一様な構造と強い乱れをもつ厚い(100nm)アモルファスMo_xSi_<1-x>膜の極低温・高磁場域におけるボルテックス状態を調べた。絶対零度(T=0)近傍までボルテックス液体相(量子ボルテックス液体[QVL]相)が存在すること,QVL相に相当する高磁場中で温度を減少させると,ある温度T_Qで抵抗の温度依存性の曲率が上凸から下凸へ変化し,T=0に向かって電気抵抗率が残るような振舞いをすることがわかった。このT_Qは熱的液体相から量子的液体相へのクロスオーバーを表す特徴的温度と解釈される。複素交流インピーダンス測定から求めたボルテックスグラス転移の動的臨界指数zはT_Qよりやや高いある温度以下で上昇するという異常が見られた。さらにQVL相の広さは,ほぼ常伝導抵抗率ρ_nに比例して磁場軸・温度軸方向に増大することもわかった。この結果は,ρ_nが量子ゆらぎを強めることを通してQVL領域の拡大をもたらすという描像と一致する。つぎに熱的液体相からQVL相への移り変わりに伴うボルテックスダイナミクスの変化を調べることを目指し,液体相においてボルテックスフロー電圧のノイズスペクトラムと電圧の時間依存性[時系列V(t)]測定を行った。極低温域のQVL相でのみ,ボルテックスフローによる(平均電圧のまわりの)電圧ゆらぎδV(t)が観測され,その分布にボルテックスの進行方向に向かって長い裾野をもつ異常な非対称性が現れることがわかった。これは,QVL相ではボルテックスの速度あるいは数が時間tの関数として断続的に増大することを示している。またここでは,大きなブロードバンドノイズが発生した。このような異常が見え始める温度は,上記のT_Qあるいはzが増大する温度と近い極低温(〜0.1K)であった。これらの実験結果から,QVL相において,熱的液体相では見られない異常なボルテックスダイナミクスが存在していることが明らかになった。

Research Products
(21 results)

All Other

All Publications (21 results)

[Publications] S.Okuma, M.Kamada, M.Kobayashi: "Crossover from thermal to quantum liquid regime in a thick amorphous film"Physica C. (印刷中).
[Publications] M.Kamada, Y.Watanabe, S.Okuma: "Unusual vortex dynamics in the Meissner phase in the Corbino disk"Physica C. (印刷中).
[Publications] S.Okuma, F.Saito, K.Amemori, M.Kobayashi: "Critical Dynamics of Vortices near the second-order transition and quantum fluctuations"Physica C. (印刷中).
[Publications] S.Okuma, K.Amemori, S.Togo: "Vorltex-Glass Transition and Vortex Phase Diagram in Thick Amorphous MG_xB_<1-x> Films"Physica C. (印刷中).
[Publications] M.Kamada, S.Okuma: "Dynamics of the Vortex Glass in the Corbino Disk Geometry"Physica C. (印刷中).
[Publications] M.Kamada, S.Okuma: "Plastic Motion of Current Driven Vortex Glass in the Corbino Disk"J.Phys.Soc.Jpn.. 73・No.3. 526-529 (2004)
[Publications] S.Okuma, S.Togo, M.Morita: "Enhancement of the Quantum-Liquid Phase by Increased Resistivity in Thick Amorphous Mo_xSi_<1-x> Films"Phys.Rev.Lett.. 91. 067001(1)-067001(4) (2003)
[Publications] S.Okuma, S.Togo, K.Amemori: "Observation of Superconductivity in Thick Amorphous Mg_xB_<1-x> Films"Phys.Rev.B. 67. 172508(1)-172508(4) (2003)
[Publications] S.Okuma, S.Togo, M.Morita, F.Saito, K.Amemori: "Quantum Fluctuations and Vortex Phase Diagram in Uniformly Disordered Amorphous Films"Int.J.Mod.Phys.B. 17. 3396-3400 (2003)
[Publications] S.Okuma, S.Togo, K.Amemori: "Superconducting Properties and Possible Vortex Phase Diagram in Thick Amorphous Mg_xB_<1-x> Films"Int.J.Mod.Phys.B. 17. 3688-3693 (2003)
[Publications] M.Morita, S.Okuma: "Magnetoresistance and Current-Induced Vortex Motion at T→O in Two-Dimensional Vortex Glass"Int.J.Mod.Phys.B. 17. 3445-3448 (2003)
[Publications] S.Okuma, S.Togo, K.Amemori: "Superconductivity and Vortex States in Thick Amorphous Mg_xB_<1-x> Films"Physica C. 392. 336-340 (2003)
[Publications] S.Okuma, F.Saito, S.Togo, M.Morita, K.Amemori: "Effects of Disorder and Dimensionality on the Vortex Phase Diagram at Low Temperature in Amorphous Films"Physica C. 392. 410-413 (2003)
[Publications] M.Morita, S.Okuma: "Magnetoresistance and Vortex States below the 2D Superconductor-Insulator Transition near T=0"Physica C. 392. 406-409 (2003)
[Publications] M.Kamada, Y.Arakawa, S.Okuma: "I-V Characteristics of Thick a-Mo_xSi_<1-x> Films in the Corbino Disk Geometry"Physica C. 392. 424-427 (2003)
[Publications] S.Okuma, M.Kamada: "Dynamics of Current-Driven Vortex Glass Probed by voltage Noise"Proc.17th International Conference on Noise and Fluctuations ICNF03, Prague, Czech Republic. 179-182 (2003)
[Publications] S.Okuma, F.Saito, M.Morita: "Suppression of the Vortex-Glass Phase in Quasi-2D a-Mo_xSi_<1-x> Films"J.Low Temp.Phys.. 131. 1019-1023 (2003)
[Publications] S.Okuma, S.Togo, D.Sanno, K.Amemori, M.Morita: "Superconducting Properties in Amorphous Mg_xB_<1-x> Films"J.Low Temp.Phys.. 131. 1111-1115 (2003)
[Publications] S.Okuma, S.Togo, M.Morita: "Vortex States at Low Temperature and Disorder in Thick a-Mo_xSi_<1-x> Films"Physica B. 329-333. 1389-1390 (2003)
[Publications] M.Morita, S.Okuma: "Anomalous Magnetoresistance below the 2D superconductor-Insulator Transition"Physica B. 329-333. 1393-1394 (2003)
[Publications] M.Kamada, S.Okuma: "Vortex States just below the Vortex-Glass Phase Probed by Voltage Noise"Physica C. 388-389. 783-784 (2003)

2003 Fiscal Year Annual Research Report

乱れた超伝導体の極低温ボルテックス状態と量子ゆらぎ

Principal Investigator

大熊 哲 東京工業大学, 極低温物性研究センター, 助教授 (50194105)

Research Products

[Publications] S.Okuma, M.Kamada, M.Kobayashi: "Crossover from thermal to quantum liquid regime in a thick amorphous film"Physica C. (印刷中).

[Publications] M.Kamada, Y.Watanabe, S.Okuma: "Unusual vortex dynamics in the Meissner phase in the Corbino disk"Physica C. (印刷中).

[Publications] S.Okuma, F.Saito, K.Amemori, M.Kobayashi: "Critical Dynamics of Vortices near the second-order transition and quantum fluctuations"Physica C. (印刷中).

[Publications] S.Okuma, K.Amemori, S.Togo: "Vorltex-Glass Transition and Vortex Phase Diagram in Thick Amorphous MG_xB_<1-x> Films"Physica C. (印刷中).

[Publications] M.Kamada, S.Okuma: "Dynamics of the Vortex Glass in the Corbino Disk Geometry"Physica C. (印刷中).

[Publications] M.Kamada, S.Okuma: "Plastic Motion of Current Driven Vortex Glass in the Corbino Disk"J.Phys.Soc.Jpn.. 73・No.3. 526-529 (2004)

[Publications] S.Okuma, S.Togo, M.Morita: "Enhancement of the Quantum-Liquid Phase by Increased Resistivity in Thick Amorphous Mo_xSi_<1-x> Films"Phys.Rev.Lett.. 91. 067001(1)-067001(4) (2003)

[Publications] S.Okuma, S.Togo, K.Amemori: "Observation of Superconductivity in Thick Amorphous Mg_xB_<1-x> Films"Phys.Rev.B. 67. 172508(1)-172508(4) (2003)

[Publications] S.Okuma, S.Togo, M.Morita, F.Saito, K.Amemori: "Quantum Fluctuations and Vortex Phase Diagram in Uniformly Disordered Amorphous Films"Int.J.Mod.Phys.B. 17. 3396-3400 (2003)

[Publications] S.Okuma, S.Togo, K.Amemori: "Superconducting Properties and Possible Vortex Phase Diagram in Thick Amorphous Mg_xB_<1-x> Films"Int.J.Mod.Phys.B. 17. 3688-3693 (2003)

[Publications] M.Morita, S.Okuma: "Magnetoresistance and Current-Induced Vortex Motion at T→O in Two-Dimensional Vortex Glass"Int.J.Mod.Phys.B. 17. 3445-3448 (2003)

[Publications] S.Okuma, S.Togo, K.Amemori: "Superconductivity and Vortex States in Thick Amorphous Mg_xB_<1-x> Films"Physica C. 392. 336-340 (2003)

[Publications] S.Okuma, F.Saito, S.Togo, M.Morita, K.Amemori: "Effects of Disorder and Dimensionality on the Vortex Phase Diagram at Low Temperature in Amorphous Films"Physica C. 392. 410-413 (2003)

[Publications] M.Morita, S.Okuma: "Magnetoresistance and Vortex States below the 2D Superconductor-Insulator Transition near T=0"Physica C. 392. 406-409 (2003)

[Publications] M.Kamada, Y.Arakawa, S.Okuma: "I-V Characteristics of Thick a-Mo_xSi_<1-x> Films in the Corbino Disk Geometry"Physica C. 392. 424-427 (2003)

[Publications] S.Okuma, M.Kamada: "Dynamics of Current-Driven Vortex Glass Probed by voltage Noise"Proc.17th International Conference on Noise and Fluctuations ICNF03, Prague, Czech Republic. 179-182 (2003)

[Publications] S.Okuma, F.Saito, M.Morita: "Suppression of the Vortex-Glass Phase in Quasi-2D a-Mo_xSi_<1-x> Films"J.Low Temp.Phys.. 131. 1019-1023 (2003)

[Publications] S.Okuma, S.Togo, D.Sanno, K.Amemori, M.Morita: "Superconducting Properties in Amorphous Mg_xB_<1-x> Films"J.Low Temp.Phys.. 131. 1111-1115 (2003)

[Publications] S.Okuma, S.Togo, M.Morita: "Vortex States at Low Temperature and Disorder in Thick a-Mo_xSi_<1-x> Films"Physica B. 329-333. 1389-1390 (2003)

[Publications] M.Morita, S.Okuma: "Anomalous Magnetoresistance below the 2D superconductor-Insulator Transition"Physica B. 329-333. 1393-1394 (2003)

[Publications] M.Kamada, S.Okuma: "Vortex States just below the Vortex-Glass Phase Probed by Voltage Noise"Physica C. 388-389. 783-784 (2003)

大熊哲東京工業大学, 極低温物性研究センター, 助教授 (50194105)