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首页> 外文学位 >Scanning tunneling spectroscopy on superconducting yttrium barium copper oxide thin-films: Effects of calcium-doping, quasiparticle spin-injection, applied current, and magnetic field.
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Scanning tunneling spectroscopy on superconducting yttrium barium copper oxide thin-films: Effects of calcium-doping, quasiparticle spin-injection, applied current, and magnetic field.

机译：超导钇钡氧化铜薄膜上的扫描隧道光谱：钙掺杂，准粒子自旋注入，施加电流和磁场的影响。

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摘要

Low temperature scanning tunneling spectroscopy was performed on YBa2Cu3O 7-delta thin films as a function of Ca-doping, quasiparticle spin-injection, applied currents and magnetic fields. The purpose of these separate investigations was to gain insight on the microscopic pairing mechanism by examining how the superconducting order parameter (OP) evolves under these perturbations.;Applied current experiments were performed on optimally doped (110)- and (001)-oriented YBa2Cu3O7-delta films using a pulsed technique. The current suppresses the phase-sensitive Andreev states, while leaving the pairing-dependent features largely unaffected. These results indicate that applied currents can weaken the phase of the superconducting order parameter, suggesting that phase-fluctuations can be easily induced in the cuprates.;A doping dependent study was performed on (001)-oriented Y1- xCaxBa2Cu3O 7-delta thin films at x = 0, 0.05, 0.15 and 0.20 Ca levels, which enabled access to the overdoped regime. The measured spectra exhibited main-gap, subgap and satellite features which scale similarly in energy as a function of Ca-doping, suggesting that they are associated with a common pairing energy. The spectral data was analyzed using a multiband model which attributes the subgap features to the chain band and the main-gap and satellite features to the plane band for dx2--y 2 + s pairing symmetry. These results suggest that the superconductivity in YBa2Cu3O 7-delta involves multiple bands.;Lastly, the evolution of the Andreev states in applied magnetic field was examined in Ca-doped (110)-oriented Y1-xCa xBa2Cu3O7-delta thin films. A splitting of the zero-bias conductance peak is observed in both zero and non-zero applied fields, indicating a lifting of the degeneracy of the Andreev states, consistent with the presence of a subdominant complex is/id' OP component near the (110) surface. However, local signatures of time-reversal symmetry breaking associated with the presence of a subdominant, complex OP component have yet to be observed. These results will be discussed within the theoretical framework of complex subdominant order parameter components in the high-Tc cuprates.;Quasiparticle spin-injection experiments were performed on thin film heterostructures comprised of optimally doped YBa2Cu3O7-delta and ferromagnetic La0.66Ca0.33MnO3, using a technique which combines scanning tunneling spectroscopy and pulsed spin-injection. A spectral redistribution of the low-energy Andreev states was observed, consistent with an elevated effective quasiparticle temperature induced by spin-injection. Our results also indicate that spin-injection at moderate densities does not induce pair breaking or variation in the predominant d-wave pairing symmetry.
机译：根据Ca掺杂，准粒子自旋注入，施加的电流和磁场，对YBa2Cu3O 7-delta薄膜进行了低温扫描隧道光谱。这些单独研究的目的是通过检查在这些扰动下超导阶数参数（OP）的演化来了解微观配对机制。;对最佳掺杂（110）和（001）取向的YBa2Cu3O7进行了应用电流实验-使用脉冲技术的胶片。电流抑制了对相位敏感的安德列夫状态，而​​与配对相关的特征却基本上不受影响。这些结果表明施加的电流可以削弱超导阶数参数的相位，表明在铜酸盐中很容易引起相位波动。;对（001）取向的Y1-xCaxBa2Cu3O 7-delta薄膜进行了掺杂依赖性研究。在x = 0、0.05、0.15和0.20 Ca水平时，可以进入过量掺杂状态。测得的光谱显示出主能隙，次能隙和卫星特征，它们的能量随Ca掺杂的变化而按比例缩放，表明它们与共同的配对能量相关。使用多频带模型分析光谱数据，该模型将子间隙特征归因于链带，将主间隙特征和卫星特征归因于平面带，以实现dx2--y 2 + s的配对对称性。这些结果表明，YBa2Cu3O7-δ中的超导性涉及多个带。最后，在Ca掺杂（110）取向的Y1-xCaxBa2Cu3O7-δ薄膜中研究了施加磁场中Andreev态的演化。在零和非零施加场中都观察到零偏导率峰的分裂，表明安德列夫状态的简并性提升，这与在（110）附近存在主要复合物is / id'OP分量一致）表面。然而，与次要的，复杂的OP成分的存在相关的时间反转对称性破坏的局部特征尚未观察到。这些结果将在高Tc铜酸盐中复杂的次要参数组分的理论框架内进行讨论。;使用由最佳掺杂的YBa2Cu3O7-δ和铁磁La0.66Ca0.33MnO3组成的薄膜异质结构进行了准粒子自旋注入实验，使用一种结合了扫描隧道光谱和脉冲自旋注入的技术。观察到低能安德列夫态的光谱重新分布，这与自旋注入引起的有效准粒子温度升高一致。我们的结果还表明，以中等密度自旋注入不会引起成对断裂或主要d波对对称性的变化。

著录项

  • 作者

    Ngai, Joseph Ho Yeen.;

  • 作者单位

    University of Toronto (Canada).;

  • 授予单位 University of Toronto (Canada).;
  • 学科 Physics Condensed Matter.
  • 学位 Ph.D.
  • 年度 2007
  • 页码 125 p.
  • 总页数 125
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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