EAPSI: Investigating the Electronic Properties of Topological Insulator in the Presence of Magnetic Impurities

拓扑绝缘体（TI）是量子物质的一种新相。TI是独特的，因为它们具有绝缘体以及导电边缘。这些边缘无损耗地传输能量和信息，无论其长度如何。这些特性非常强大，改变它们的唯一方法是引入磁性杂质。本计画将制作一个可由金属边缘状态转变为绝缘边缘结构的可调系统。这项研究将与韩国浦项科技大学的Woong Yeom Han教授的团队合作进行，该团队是世界上少数几个能够制造和表征二维拓扑绝缘体的团队之一。因此，这种合作提供了一个独特的环境来表征和制造可调拓扑绝缘系统。TI受时间反演对称性保护。这种对称性可以承受任何缺陷和损坏，除了破坏时间反演对称性的磁性杂质。因此，要真正控制拓扑绝缘体的电子性质，必须了解其在磁性杂质存在下的行为。虽然二维TI与磁缺陷的理论研究已经预测，时间反转打破磁缺陷打开一个间隙，否则无间隙的边缘状态，一直没有实验研究报告，以验证这一假设。本计画的主要目的是利用扫描隧道显微镜（STM）在近藤杂质存在下，在Bi2Te2Se上制作出拓扑绝缘的Bi（111）双层膜，并加以表征。这个NSF EAPSI奖是与韩国国家研究基金会合作资助的。

A topological insulator (TI) is a new phase of quantum matter. TIs are unique since they have insulating bulk as well as conducting edges. These edges transmit energy and information without loss, regardless of their length. These properties are very robust and the only way to change them is by introducing magnetic impurities. This project will fabricate a tunable system that can be changed from a metallic edge state to an insulating edge structure. The research will be conducted in collaboration with Professor Woong Yeom Han's group at Pohang University of Science and Technology in South Korea, one of the few groups in the world capable of fabricating and characterizing two-dimensional topological insulators. Hence, this collaboration provides a unique environment to characterize and fabricate a tunable topological insulating system. TIs are protected by time-reversal symmetry. This symmetry can withstand any defects and damage with the exception of magnetic impurities that break time-reversal symmetry. Therefore, to truly control the electronic properties of a topological insulator, one must understand its behavior in the presence of magnetic impurities. Although theoretical studies of two-dimensional TIs with magnetic defects have predicted that time-reversal breaking magnetic defects open a gap in the otherwise gapless edge state, there has been no experimental studies reported to verify this hypothesis. This project is focused on fabricating and characterizing a topological insulating Bi(111) bilayer on Bi2Te2Se in the presence of Kondo impurities using a scanning tunneling microscope (STM). This NSF EAPSI award is funded in collaboration with the National Research Foundation of Korea.