Emergent Quantum Phenomena in Topological Kondo Insulators

非技术摘要该奖项来自材料研究部的凝聚态物理计划，支持对一类称为拓扑绝缘体的新材料的电子特性的研究。拓扑绝缘体是一种不寻常的量子态，其中材料的大部分是电绝缘体，而表面是一种导体，可以稳定地抵抗各种外部扰动。拓扑绝缘体在过去的几年里产生了巨大的科学兴奋，因为新颖的电性能和它们作为先进电子器件在量子计算和自旋输运等领域的潜在应用。然而，由于材料中不可避免的缺陷，迄今为止发现的所有材料都具有非绝缘体输运行为;因此，它们没有表现出理想或有用的拓扑性质。最近的一个理论表明，一类特殊的材料，称为近藤绝缘体，将是一种具有真正体绝缘状态的拓扑绝缘体。马里兰州大学的研究人员对已知近藤绝缘体的电子特性进行测量，以研究其可能的拓扑行为，并测试其对新的和新颖的电子应用的适用性。该研究项目涉及对本科生和研究生进行先进测量技术和材料物理学前沿科学知识的培训。技术摘要马里兰州大学的研究人员正在进行不同近藤绝缘体系统中电子输运现象的实验研究，这些绝缘体系统在理论上被认为具有拓扑表面状态。了解拓扑绝缘体的新性质以及强电子关联对拓扑性质的作用是凝聚态物理中的一个重要基础科学问题。 最近在近藤绝缘体SmB 6中发现的表面金属态表明可能存在强相关的TI。然而，尽管最近在SmB 6中发现了许多非常规的传输现象，但非平凡拓扑表面状态的“确凿证据”尚未建立。 这项研究强调了薄膜和单晶在低温（低至20 mK）下的输运性质，其中新的量子涌现现象预计将是突出的。 该项目使用点接触光谱，静电场效应研究，高磁场传输测量和微波和光学测量有前途的KI材料。该项目的一个重要推动力是邻近效应的研究，因为它已经预测，将拓扑绝缘体与铁磁绝缘体和/或传统超导体结合可能会导致奇异的性质，如马约拉纳费米子激发。这些测量所需的所有材料都在内部合成和表征。该研究项目涉及对本科生和研究生进行先进测量技术和材料物理学前沿科学知识的培训。

Non-Technical AbstractThis award from the Condensed Matter Physics program of the Division of Materials Research supports research on the electronic properties of a new class of material known as Topological Insulators. A topological insulator is an unusual quantum state in which the bulk of the material is an electrical insulator, while the surface is a conductor that is stable against various external perturbations. Topological insulators have generated great scientific excitement over the past few years because of the novel electrical properties and their potential application as advanced electronic devices in areas such as quantum computation and spin transport. However, all of the materials discovered to date have a non-insulating bulk transport behavior because of unavoidable defects in the material; therefore, they do not exhibit ideal or useful topological properties. A recent theory has suggested that a special class of material, known as a Kondo insulator, would be a topological insulator with a true bulk insulating state. Researchers at the University of Maryland conduct measurements of the electronic properties of known Kondo insulators to investigate their possible topological behavior and to test their suitability for new and novel electronic applications. This research project involves the training of undergraduate and graduate students in advanced measurement techniques and in cutting edge scientific knowledge of materials physics.Technical AbstractResearchers at the University of Maryland are undertaking experimental studies of electronic transport phenomena in different Kondo insulator systems that are theoretically suggested to harbor topological surface states. Understanding the novel properties of topological insulators and the role of strong electron correlations on topological properties is a major basic science problem in condensed matter physics. The recent discovery of a surface metallic state in the Kondo insulator SmB6 suggests that strongly correlated TIs may exist. However, despite many unconventional transport phenomena recently found in SmB6, the "smoking gun" evidence for a nontrivial topological surface state has yet to been established. This study emphasizes the transport properties of thin films and single crystals at low temperatures (down to 20 mK), where novel emergent quantum phenomena are expected to be prominent. The project uses point contact spectroscopy, static electric field effect studies, and high magnetic field transport measurements and microwave and optical measurements on promising KI materials. An important thrust of this project is the study of the proximity effect, since it has been predicted that incorporating topological insulators with ferromagnetic insulators and/or conventional superconductors may lead to exotic properties such as Majorana fermion excitations. All the materials required for these measurements are being synthesized and characterized in-house. This research project involves the training of undergraduate and graduate students in advanced measurement techniques and in cutting edge scientific knowledge of materials physics.