EAGER: Study of Helical Spin Structure of Topologically Protected Surface States on Samarium Hexaboride

非技术摘要：人们对一种被称为拓扑绝缘体的新型材料系统越来越感兴趣，这种材料系统具有拓扑保护的导电表面状态。形成这些受拓扑保护的状态的电荷预计将具有迷人的性质，这些性质源于它们在运动时被迫旋转的方式。该项目将通过对六硼化钐进行直接自旋检测实验来探索这些独特的性质，也就是众所周知的螺旋自旋结构。六硼化钐在低温下的块体中没有电荷，并测试依赖于拓扑表面态的独特性质的新器件概念。在教育方面，该项目将为研究生和本科生提供出色的培训。首席研究人员还将利用密歇根大学现有的REU和硕士桥梁项目，从代表不足的群体中引进一名学生加入这个项目。技术摘要：人们对一种被称为拓扑绝缘体的新材料系统越来越感兴趣，这种材料系统具有拓扑保护的导电表面态。由于表面电子的螺旋自旋结构，拓扑绝缘体表面的输运性质被认为是非常独特的。尽管这种表面态已经在许多材料中看到，但在大多数情况下，这些材料实际上是块状导体，而不是真正的绝缘体，这使得对这些表面态的电学表征非常具有挑战性。在这个项目中，将研究六硼化钐的拓扑表面，它是最近被发现的一种相关的拓扑绝缘体，具有真正的绝缘体。螺旋自旋结构将使用特别设计的自旋注入设备来检测，该设备结合了磁隧道结，并在六硼化锶的不同表面进行了科尔比诺实验。科尔比诺和自旋注入器件将使用标准光刻技术在使用浮动区和铝助熔剂两种方法生长的高质量六硼化锶晶体上制造。输运实验将在低温和强磁场下进行。如果成功，这些实验将毫不含糊地揭示表面状态的拓扑性质。使用纯粹的输运测量来探测螺旋自旋结构对于推动磁场向前发展将是至关重要的。这些实验还将提供新的机会来研究强关联效应和拓扑学之间的相互作用，以寻找新的物理原理。该项目将为研究生和本科生提供良好的培训。首席调查员还将利用密歇根大学现有的REU和硕士桥项目，从代表不足的群体中引入一名学生加入这个项目。

Non-technical Abstract: There has been growing interest in a new class of material system known as topological insulators, which are known to harbor topologically protected conducting surface states. The charges forming these topologically protected states are expected to have fascinating properties arising from the way they are forced to spin as they are moving. The project will explore these unique properties, also known as the helical spin structure, by performing direct spin detection experiments on samarium hexaboride, which has no charges in its bulk at cryogenic temperatures and test new device concepts that rely on unique properties of topological surface states. On the educational side, the project will provide excellent training for graduate and undergraduate students. The principal investigator will also be leveraging University of Michigan's existing REU and Master's bridge programs to bring in a student from an underrepresented group to join this project.Technical Abstract: There has been growing interest in a new class of material system known as topological insulators, which are known to harbor topologically protected conducting surface states. The transport properties of the surface of topological insulators are expected to be quite unique, arising from the helical spin structure of surface electrons. Even though such surface states have been seen in many materials, in most cases these materials are actually bulk conductors, and not true insulators making electrical characterization of these surface states very challenging. In this project, topological surface will be studied in samarium hexaboride, which has recently been discovered to be a correlated topological insulator with a truly insulating bulk. The helical spin structure will be detected using specially designed spin injection devices incorporating magnetic tunnel junction together with Corbino experiments performed on different surfaces of samarium hexaboride. The Corbino and spin injection devices will be fabricated using standard lithographic techniques on high quality samarium hexaboride crystals grown both using floating zone and Al flux methods. The transport experiments will be performed at cryogenic temperatures and high magnetic fields. If successful, these experiments will unambiguously reveal the topological nature of surface states. Probing the helical spin structure using purely transport measurements will be critically important in moving the field forward. These experiments will also provide new opportunities to study the interplay between strong-correlation effects and topology in the search for new principles of physics. The project will provide excellent training for the graduate and undergraduate students. The principal investigator will also be leveraging University of Michigan's existing REU and Masters bridge programs to bring in a student from an underrepresented group to join this project.