Thermodynamic study of mixed states of quasi-two-dimensional superconductors

准二维超导体混合态的热力学研究

• 批准号: 07650004
• 负责人: HANAGURI Tetsuo
• 金额: $ 1.54万
• 依托单位: The University of Tokyo
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 1995
• 资助国家: 日本
• 起止时间: 1995 至 1996
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-07650004/
• 关键词: High-Tc superconductor; Mixed state; Heat capacity; Magnetization; Noise; 磁束融解転移; 磁束液体; ピン止め; 磁束密度ゆらぎ; Josephsonプラズマ; 相転移; 局所磁場分布

By measuring various thermodynamic and dynamic quantities, we studied the nature of vortices in layred superconductors, especially in Bi_2Sr_2CaCu_2O_y. As for the thermodynamic measurements, we observed the magnetization jump at the first-order-vortex-melting transition. From the measurements on the samples with different oxygen contents, we revealed that the melting line is affected by the anisotropy of the system. However, we could not detect the specific heat anomalies at the transition because the entropy change at the transition was too small.As for the dynamic measurements, we performed the simultaneous measurements of the local magnetization and resistivity. We found that the resistivity in the vortex liquid phase is non-ohmic just above the melting transition. This result suggests that pining is still relevant even in the liquid phase because of the high viscosity of the liquid. Moreover, we developed a novel technique to measure the noise of the local vortex density using a miniature Hall probe and an FFT analyzer. We found a large noise when the vortices start moving. Such a noise was observed even in the vortex liquid phase, which is a further indication of the pinning in the vortex liquid. To examine the interlayr coherence of the vortices, Josephson plasma resonance was also investigated.

通过测量各种热力学和动态量，我们研究了躺置超导体中涡流的性质，尤其是在BI_2SR_2CACU_2O_Y中。至于热力学测量值，我们观察到一阶涡流熔融过渡时的磁化突变。从具有不同氧含量的样品上的测量值中，我们揭示了熔融线受系统各向异性的影响。但是，我们无法检测到过渡时的特定热异常，因为过渡时的熵变化太小。对于动态测量，我们同时进行了局部磁化和电阻率的测量。我们发现，涡流液相中的电阻率在熔融跃迁上方是非欧味的。该结果表明，由于液体的粘度很高，即使在液相中，夹紧仍然是相关的。此外，我们开发了一种新型技术，可以使用微型霍尔探针和FFT分析仪来测量局部涡流密度的噪声。当涡流开始移动时，我们发现了大噪音。即使在涡流液相中也观察到这种噪声，这进一步表明了涡流液体中的固定。为了检查涡旋的互层相干性，还研究了约瑟夫森等离子体共振。

项目成果

T.Hanaguri: "Phase transition in mixed state of Bi_2Sr_2CaCu_2O_y observed by local and macroscopic magnetometry." Czech.J.Phys.46, Suppl.S3. 1559-1560 (1996)

T.Hanaguri：“通过局部和宏观磁力测量观察到 Bi_2Sr_2CaCu_2O_y 混合态的相变。”

A.Maeda: "Josephson-plasma resonance of Bi-cuprates" Czechoslovak Journal of Physics. 46. 1635-1636 (1996)

A.Maeda：“双铜酸盐的约瑟夫森等离子体共振”捷克斯洛伐克物理学杂志。

T.Tsuboi: "Nature the vortex liquid in Bi_2Sr_2CaCu_2O_y." Phys.Rev.B. 55. R8709-R8712 (1997)

T.Tsuboi：“Bi_2Sr_2CaCu_2O_y 中的涡流液体自然。”

T.Hanaguri: "Doping level dependent magnetization anomalies and heat capacity of Bi_2Sr_2CaCu_2Ost8 in the mixed state" Physica C. (印刷中). (1996)

T. Hanaguri：“混合状态下 Bi_2Sr_2CaCu_2Ost8 的掺杂水平相关磁化异常和热容量”Physica C.（出版中）。