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A combined near-field scanning microwave microscope and transport measurement system for characterizing dissipation in conducting and high-temperature superconducting films at variable temperatures.

机译：一种组合的近场扫描微波显微镜和传输测量系统，用于表征可变温度下导电和高温超导薄膜的耗散。

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摘要

Identifying defects and non-superconducting regions in high-temperature superconductors (HTS) is of great importance because they limit the material's capability to carry higher current densities and serve as nucleation spots for "hot spots" that can evolve over time and drive a HTS from superconducting (SC) to normal state. A technique that combines near-field scanning microwave microscopy (NSMM) with transport measurement was developed to image defects and non-uniformities at room temperature and detect low-level dissipation at low temperatures. At room temperature, macroscopic and microscopic defects in both conducting and HTS films were clearly identified and imaged with adequate sensitivity and resolution. At low temperatures, low-level dissipation was detected by observing the NSMM's response during the HTS' transition from SC to normal state. Measuring the time-dependent self-heating effect due to a bias current at a fixed temperature provided insight into the dynamics of thermal instability due to hot-spot nucleation. When the HTS is far from the transition state, a bi-modal evolution of the thermal quench was observed beginning with a nucleation of a local hot spot followed by a spreading/coalescence of them via self-heating. When the HTS is brought closer to transition by increasing either temperature or bias current, this effect is diminished due to faster hot spot growth and continuous spread by self-heating. Observations were obtained for both the bulk and grain boundary regions of a HTS.
机译：识别高温超导体（HTS）中的缺陷和非超导区域非常重要，因为它们会限制材料承载更高电流密度的能力，并充当“热点”的成核斑，这些“热点”会随时间演变并驱动HTS从超导（SC）到正常状态。开发了一种将近场扫描微波显微镜（NSMM）与传输测量相结合的技术，以在室温下成像缺陷和不均匀性，并在低温下检测低电平耗散。在室温下，可以清楚地识别导电膜和高温超导膜中的宏观和微观缺陷，并以足够的灵敏度和分辨率成像。在低温下，通过观察HTS从SC过渡到正常状态期间NSMM的响应，可以检测到低水平的耗散。测量在固定温度下由于偏置电流引起的随时间变化的自热效应，可以深入了解由于热点成核而引起的热不稳定性。当HTS远离过渡态时，观察到热猝灭的双峰演变，首先是局部热点的形核，然后通过自热使它们散布/聚结。当通过增加温度或偏置电流使HTS接近转变时，由于热点增长更快以及自热持续扩散，这种影响会减弱。观察到了高温超导的体积和晶界区域。

著录项

  • 作者

    Dizon, Jonathan Reyes.;

  • 作者单位

    University of Kansas.;

  • 授予单位 University of Kansas.;
  • 学科 Physics Condensed Matter.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 127 p.
  • 总页数 127
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 O49;
  • 关键词

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