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首页> 外文学位 >Exotic phenomena in 4f systems: From complex magnetism to surface conduction.
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Exotic phenomena in 4f systems: From complex magnetism to surface conduction.

机译：4f系统中的外来现象：从复磁到表面传导。

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摘要

For materials synthesized with f-electron elements, the interaction between f-electrons and conduction electrons often leads to interesting physics. As the temperature is lowered, the f-electrons can hybridize with the conduction electrons in a process known as the Kondo effect. In a Kondo lattice material, the screening may become coherent at the so-called coherence temperature T*. The resulting material is often metallic, containing heavy bands with effective masses many times larger than the free electron mass. In some cases, the development of coherence leads to a filled heavy-electron band where the chemical potential lies within the hybridization gap, resulting in insulating behavior.;CeAgBi2 is an antiferromagnetic compound (TN = 6.4 K) belonging to the former (metallic) case. The close energy scales of the Kondo coherence, antiferromagnetism, and crystal field levels results in complex physical properties. Transport measurements reveal a coupling between the different magnetic phases and Hall resistivity. As the field is increased, the antiferromagnetic transition temperature is suppressed to zero Kelvin. Typically, this is expected to result in a quantum critical point. However, due to strange transport behavior in the paramagnetic regime, the usual signatures of quantum criticality are hidden.;SmB6 is a Kondo insulator due to the fact that the hybridization results in the opening of a gap. However, as the temperature is further lowered, the resistance saturates. Originally believed to be due to in-gap conduction states in the bulk, the true reason for the resistance saturation is a robust conducting surface state. Several theories predict that the surface state is a result of SmB6 belonging to a class of materials known as topological insulators. However, direct imaging of the spin-momentum locking of the surface states indicative of a topological insulator has proved elusive. Through transport and magnetic measurements, indirect evidence of the nature of the conducting surface state is presented.
机译：对于用f电子元素合成的材料，f电子与传导电子之间的相互作用通常会引起有趣的物理学。随着温度降低，f电子可以在称为近藤效应的过程中与传导电子杂交。在近藤晶格材料中，屏蔽可以在所谓的相干温度T *下变得相干。所得材料通常是金属的，包含重带，其有效质量是自由电子质量的许多倍。在某些情况下，相干的发展导致化学势位于杂交间隙内的重电子带被填充，从而导致绝缘行为。; CeAgBi2是反铁磁化合物（TN = 6.4 K），属于前者（金属）案件。近藤相干性，反铁磁性和晶体场能级的紧密能级导致复杂的物理性质。输运测量揭示了不同磁相与霍尔电阻率之间的耦合。随着磁场的增加，反铁磁转变温度被抑制为零开尔文。通常，这预计会导致量子临界点。然而，由于在顺磁性条件下的奇怪的输运行为，隐藏了通常的量子临界特征。由于杂化导致间隙的开放，SmB6是近藤绝缘子。但是，随着温度的进一步降低，电阻饱和。最初被认为是由于整体中的间隙内导电状态引起的，电阻饱和的真正原因是坚固的导电表面状态。几种理论预测，表面状态是SmB6的结果，SmB6属于一类称为拓扑绝缘体的材料。但是，证明对表示拓扑绝缘体的表面状态的自旋动量锁定进行直接成像已难以捉摸。通过传输和磁测量，可以提供有关导电表面状态性质的间接证据。

著录项

  • 作者

    Thomas, Sean Michael.;

  • 作者单位

    University of California, Irvine.;

  • 授予单位 University of California, Irvine.;
  • 学科 Condensed matter physics.
  • 学位 Ph.D.
  • 年度 2016
  • 页码 96 p.
  • 总页数 96
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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