Tailoring and probing electronic/magnetic structure of engineered magnetic topological insulators

工程磁拓扑绝缘体的电子/磁结构的定制和探测

• 批准号: 2219610
• 负责人: Chih-Kang Shih
• 金额: $ 47.28万
• 依托单位: University of Texas at Austin
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-09-01 至 2025-08-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2219610&HistoricalAwards=false
• 关键词: Tailoring; probing; electronic; magnetic; structure

Non-technical Abstract: Remarkable properties of topological materials, such as ability to conduct electric current without dissipation, were first discovered four decades ago, but only under extreme experimental conditions of nearly absolute zero temperature and high magnetic field. It was subsequently recognized that such a remarkable transport property is derived from material “topology”. This recognition has launched the era of topological quantum materials with the potential to realize the remarkable properties at a much higher temperature without an external magnetic field. There are, however, several technical challenges that need to be overcome before bringing such technical promises to reality. This research program is set up to address some of the most important materials science issues and to lay the foundations for tailoring the new class of magnetic topological insulators using multi-layered heterostructures. Educationally, the PI will create a new course beyond the current curriculum to provide students with academic training so they can be well-prepared to enter this new exciting research field of topological quantum materials. Technical Abstract: In magnetic topological insulators (MTI), the incorporation of magnetism breaks the time reversal symmetry and creates a Dirac mass gap in the otherwise massless surface states of topological insulators (TI). In MTI remarkable transport properties such as quantum anomalous Hall effect (QAHE) have been predicted and observed in extrinsic MTI materials (i.e. TI with magnetic dopants). However, due to the dopant disorder effect, the QAHE can be observed only at a very low temperature (~ 30 mK). The newly emerged intrinsic MTI materials such as MnBi2Te4 (MBT) offers an alternative platform by incorporating a stoichiometric magnetic layer (MnTe) into the center of Bi2Te3. An ideal intrinsic MTI would be free of dopant disorder, thus offering the possibility to observe QAHE up to the magnetic transition temperature. Already several groups have reported observation of QAHE at ~ 1K, significantly higher than that in extrinsic MTI, albeit still smaller than the magnetic transition temperature (~ 20K). These earlier works have stimulated intensive worldwide research work. However, several outstanding issues remain unresolved. Meanwhile, efforts have been devoted to designing new magnetic topological quantum materials beyond simple MBT and related compounds. This project combines molecular beam epitaxy with in-situ scanning probe microscopy to study artificially engineered MTI and MTI/TI heterostructures. The object is three-fold: (a) controlling the formation of MTI and MTI/TI heterostructure layer-by-layer with ultimate control in defect density and chemical potential; (b) resolving key outstanding issues that challenge the current understanding of the connection between the topological surface states and the magnetic textures; (c) determining key designing parameters for artificial engineering of topological properties using MTI/TI superlattices. Educationally, the graduate students trained in this research program gain a broad scientific perspective. Through the design of a special course in topological quantum materials, the PI will significantly broaden graduate/undergraduate education in contemporary condensed matter physic. The program also broadens the participation of underrepresented groups.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

非技术摘要：拓扑材料的显着特性，例如在不耗散的情况下传导电流的能力，在四十年前首次被发现，但只有在几乎绝对零温度和高磁场的极端实验条件下才被发现。卓越的传输特性源自材料“拓扑”，这种认识开启了拓扑量子材料的时代，该材料有可能在没有外部磁场的情况下在更高的温度下实现卓越的特性。在带来这样的问题之前需要克服该研究计划旨在解决一些最重要的材料科学问题，并为使用多层异质结构定制新型磁性拓扑绝缘体奠定基础。在教育方面，PI 将创建一门新课程。超越当前课程，为学生提供学术培训，使他们能够为进入拓扑量子材料这一令人兴奋的新研究领域做好充分准备。 技术摘要：在磁性拓扑绝缘体（MTI）中，磁性的结合打破了时间。反转对称性并在拓扑绝缘体 (TI) 的无质量表面态中产生狄拉克质量隙。在 MTI 中，在外在 MTI 材料（即具有磁性掺杂剂的 TI）中预测并观察到了显着的输运特性，例如量子反常霍尔效应 (QAHE)。然而，由于掺杂剂无序效应，QAHE只能在非常低的温度（~30 mK）下观察到。新出现的本征MTI材料如MnBi2Te4 (MBT) 通过将化学计量磁性层 (MnTe) 合并到 Bi2Te3 的中心来提供替代平台，理想的本征 MTI 不会出现掺杂紊乱，从而提供了在高达几个磁转变温度下观察 QAHE 的可能性。研究小组报告了在〜1K下观察到的QAHE，显着高于外在MTI，但仍然小于磁转变温度（〜20K）。然而，一些悬而未决的问题仍然没有得到解决，同时，该项目致力于将分子束外延与原位扫描探针显微镜相结合来设计新的磁性拓扑量子材料。工程化MTI和MTI/TI异质结构的目标有三个：（a）逐层控制MTI和MTI/TI异质结构的形成，最终控制缺陷密度和化学势；解决挑战当前对拓扑表面态与磁性纹理之间联系的理解的关键突出问题；(c) 使用 MTI/TI 超晶格确定拓扑特性人工工程的关键设计参数。通过设计拓扑量子材料的特殊课程，该项目将显着拓宽当代凝聚态物理学的研究生/本科生教育。该项目还扩大了代表性不足的群体的参与。通过使用基金会的智力价值和更广泛的影响审查标准进行评估，NSF 的法定使命被认为值得支持。

项目成果

Visualizing the interplay of Dirac mass gap and magnetism at nanoscale in intrinsic magnetic topological insulators

可视化本征磁性拓扑绝缘体中纳米级狄拉克质量间隙和磁性的相互作用

• DOI: 10.1073/pnas.2207681119
• 发表时间: 2022-10-18
• 期刊: Proceedings of the National Academy of Sciences of the United States of America
• 影响因子: 11.1
• 作者: M. Liu;C. Lei;Hyunsue Kim;Yanxing Li;Lisa Frammolino;Jiaqiang Yan;A. Macdonald;C. Shih
• 通讯作者: C. Shih