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Investigation of half-quantized fluxoid states in strontium ruthenate mesoscopic superconducting rings.

机译：钌酸锶介观超导环中半定量磁通态的研究。

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摘要

Spin-triplet superconductors can support exotic objects, such as chiral edge currents and half-quantum vortices (HQVs) characterized by the nontrivial winding of the spin structure. In this dissertation, we present cantilever magnetometry measurements performed on mesoscopic samples of Sr2RuO 4, a spin-triplet superconductor.;Satisfying the total anti-symmetric property of the Cooper pair wave function, Sr2RuO4 is theoretically suggested to have angular momentum L = 1 and form domain structure with px ± ipy order parameter that corresponds to Lz = ±1. For micron-size samples, only a few number of domains would exist and signatures of domain walls and edge currents are expected to be measurable with current sensitivity. From the measurements of fluctuations of magnetic signal and the signatures of vortex entries, we found no evidence to support broken time-reversal symmetry (TRS) in these crystals. We argue that various scenarios exist to explain the negative result while still assuming the TRS breaking chiral order parameter.;Also, micron-size annular-shaped Sr2RuO4 crystals were used to observe transitions between fluxoid states. Our observation of half-integer transitions is consistent with the existence of HQVs in a spin-triplet superconductor. Stability of the half states with an in-plane magnetic field is explained by the spin polarization in consequence of a differential phase winding of up and down spin components. These spin and charge dynamics can also be revealed in the current response to phase winding across a weak-link junction. The junctions were fabricated within ring geometry. The phase is varied by the external magnetic field and the current is calculated by measuring the magnetic moments of the ring. The current response shows second harmonics when the in-plane magnetic field is applied, and the data are successfully fitted when Gibbs free energy is expressed with additional spin degree of freedom.;Our observations are consistent with spin-triplet pairing of the Sr 2RuO4, while requiring more investigations to confirm px ± ipy order parameter in the crystal.
机译：自旋三重态超导体可以支持奇异的物体，例如以自旋结构的平凡绕组为特征的手性边缘电流和半量子涡旋（HQV）。在本文中，我们提出了对自旋三重超导体Sr2RuO 4的介观样品进行的悬臂磁强测量。满足Cooper对波函数的全部反对称特性，理论上建议Sr2RuO4具有角动量L = 1且形成具有px±ipy顺序参数的域结构，该参数对应于Lz =±1。对于微米大小的样品，将仅存在几个畴，并且预期通过电流灵敏度可以测量畴壁和边缘电流的信号。通过测量磁信号的波动和涡旋进入的特征，我们发现没有证据支持这些晶体中破碎的时间反转对称性（TRS）。我们认为存在各种情况来解释负结果，同时仍然假设TRS打破了手征阶参数。此外，微米级环形Sr2RuO4晶体被用来观察磁通态之间的跃迁。我们对半整数跃迁的观察与自旋三重态超导体中HQV的存在是一致的。平面内磁场对半态的稳定性由自旋极化来解释，这是由于上下自旋分量的差分相位绕组的结果。这些自旋和电荷动力学特性还可以在对弱连接结上的相绕组的电流响应中得到揭示。在环形几何形状内制造结。通过外部磁场改变相位，并通过测量环的磁矩来计算电流。当施加面内磁场时，电流响应显示二次谐波;当吉布斯自由能表示为具有额外的自旋自由度时，数据成功拟合;我们的观察结果与Sr 2RuO4的自旋三重态配对一致，同时需要进行更多研究以确认晶体中的px±ipy阶参数。

著录项

  • 作者

    Jang, Joonho.;

  • 作者单位

    University of Illinois at Urbana-Champaign.;

  • 授予单位 University of Illinois at Urbana-Champaign.;
  • 学科 Physics Quantum.;Physics Condensed Matter.
  • 学位 Ph.D.
  • 年度 2012
  • 页码 109 p.
  • 总页数 109
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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