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

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。形成这些拓扑保护态的电荷有望具有迷人的特性，这些特性来自于它们在运动时被迫自旋的方式。该项目将通过在六硼化钐上进行直接自旋检测实验来探索这些独特的性质，也被称为螺旋自旋结构，六硼化钐在低温下没有电荷，并测试依赖于拓扑表面态独特性质的新设备概念。在教育方面，该项目将为研究生和本科生提供优秀的培训。首席研究员还将利用密歇根大学现有的REU和硕士桥梁项目，从一个代表性不足的群体中招募一名学生加入该项目。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。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。尽管这种表面状态已经在许多材料中被发现，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，这使得这些表面状态的电学表征非常具有挑战性。在这个项目中，拓扑表面将研究六硼化钐，它最近被发现是一种具有真正绝缘体的相关拓扑绝缘体。螺旋自旋结构将使用特殊设计的自旋注入装置，结合磁隧道结和Corbino实验在六硼化钐的不同表面进行检测。Corbino和自旋注入装置将使用标准光刻技术在高质量的六硼化钐晶体上制造，这些晶体采用浮动区和Al通量法生长。输运实验将在低温和强磁场条件下进行。如果成功，这些实验将明确地揭示表面态的拓扑性质。利用纯输运测量来探测螺旋自旋结构对于推动该领域的发展至关重要。这些实验也将为研究强相关效应和拓扑学之间的相互作用提供新的机会，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。首席研究员还将利用密歇根大学现有的REU和硕士桥梁项目，从一个代表性不足的群体中招募一名学生加入该项目。

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.