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Optical studies of ultrafast carrier dynamics in high temperature superconductors.

机译：高温超导体中超快载流子动力学的光学研究。

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摘要

In this thesis, I present time-resolved femtosecond optical pump-probe spectroscopy experiments and ultrafast photoresponse experiments for carrier dynamics studies in high temperature superconductors. After demonstrating experimental setup and general review of carrier dynamics in superconductors, the main experimental results are presented.; In pump-probe measurements, the optical excitation from the pump pulse perturbs the electron distribution near the Fermi surface and induces changes of optical properties. Consequently, by measuring the optical properties using probe pulses, tune-resolved carrier dynamics can be directly measured. I present pump-probe studies in superconducting HgBa2Ca2Cu 3O8 + delta thin films and MgB2 thin films. The measured optical signals are strongly related to the presence of a superconducting energy gap in the electronic energy spectrum. Carrier dynamics is studied at different temperatures and different excitation levels. Signatures of superconducting phase transition at the critical temperature (Tc) are observed in both materials. In HgBa2Ca2Cu3 O8 + delta, measured signals in superconducting state are only related to the Cooper pair breaking and recombination dynamics under weak excitation. In MgB2 however, the measured signals are always composed of several different processes and it is necessary to separate and study each process individually, in order to elucidate the dynamics in the superconducting state.; In ultrafast photoresponse measurements of YBCO microbridges, voltage transients of a current-biased YBCO structure are measured using an electro-optic sampling system. At temperatures much lower than Tc, the nonequilibrium kinetic inductive response due to the change of the superfluid is observed. A new model based on second quantization is proposed to account for damped oscillations observed in experimentally measured voltage transients. The model shows excellent agreement with the experimental data. The high excitation situation is also discussed, and a combination of a nonequilibrium kinetic inductive response and a resistive response is used to account for the measured voltage transients.
机译：在这篇论文中，我提出了时间分辨的飞秒光泵浦探针光谱实验和超快光响应实验，用于高温超导体中的载流子动力学研究。在演示了实验装置并对超导体中的载流子动力学进行了一般回顾之后，提出了主要的实验结果。在泵浦探针测量中，来自泵浦脉冲的光激发会扰乱费米表面附近的电子分布，并引起光学性质的变化。因此，通过使用探测脉冲测量光学特性，可以直接测量调谐分辨的载流子动力学。我介绍了超导HgBa2Ca2Cu 3O8 +δ薄膜和MgB2薄膜的泵浦探针研究。测得的光信号与电子能谱中超导能隙的存在密切相关。研究了在不同温度和不同激发水平下的载流子动力学。在两种材料中均观察到临界温度（Tc）下超导相变的特征。在HgBa2Ca2Cu3 O8 +δ中，处于超导状态的测量信号仅与弱激励下的库珀对断裂和重组动力学有关。然而，在MgB2中，被测信号总是由几个不同的过程组成，因此有必要对每个过程进行单独的研究，以阐明超导状态下的动力学。在YBCO微桥的超快速光响应测量中，使用电光采样系统测量了电流偏置YBCO结构的电压瞬变。在远低于Tc的温度下，观察到由于超流体的变化引起的非平衡动力学感应响应。提出了一种基于第二量化的新模型，以解决在实验测量的电压瞬变中观察到的阻尼振荡。该模型与实验数据显示出极好的一致性。还讨论了高励磁情况，并使用非平衡动态感应响应和电阻响应的组合来说明所测得的电压瞬变。

著录项

  • 作者

    Xu, Ying.;

  • 作者单位

    The University of Rochester.;

  • 授予单位 The University of Rochester.;
  • 学科 Physics Condensed Matter.; Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2004
  • 页码 98 p.
  • 总页数 98
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 工程材料学;
  • 关键词

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