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，例如在四十年前发现无耗散电流的能力，但仅在几乎绝对的零温度和高磁场的极端实验条件下发现。随后，人们认识到这种出色的运输特性源自物质“拓扑”。这种识别已经推出了拓扑量子材料的时代，有可能在没有外部磁场的情况下在更高的温度下实现出色的特性。但是，在将这种技术承诺带入现实之前，需要克服一些技术挑战。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的磁性拓扑绝缘子的基础。在教育上，PI将创建一个新课程，而不是当前目前的学术培训，以便为学生提供充分的准备，以便进入这个新的令人兴奋的拓扑量子材料研究领域。技术摘要：在磁性拓扑绝缘子（MTI）中，磁性的编码破坏了时间逆转对称性，并在原本无质量的拓扑绝缘子（TI）的无质量表面状态下产生了狄拉克质量间隙。在MTI出色的转运特性中，如量子异常效应（QAHE）的预测并在外部MTI材料（即带有磁性掺杂剂的Ti）中观察到。但是，由于掺杂症的效果，只能在非常低的温度（〜30 mk）下观察到QAHE。新出现的内在MTI材料（例如MNBI2TE4（MBT））通过将化学计量磁性层（MNTE）纳入BI2TE3中心，提供了替代平台。理想的内在MTI将没有掺杂症，这提供了观察到Qahe到磁过渡温度的可能性。已经有几个小组报告了〜1k的Qahe的观察，显着高于外部MTI，尽管仍然小于磁过渡温度（〜20K）。这些早期的作品刺激了全球研究工作。但是，几个未解决的问题仍未解决。同时，努力已致力于设计新的磁性拓扑量子材料，而不是简单的MBT和相关化合物。该项目将分子束外延与原位扫描探针显微镜结合在一起，以研究人工设计的MTI和MTI/Ti异质结构一层层次，并在缺陷密度和化学潜力方面具有最终的控制； （b）解决关键问题，以挑战当前对拓扑表面状态与磁纹理之间联系的理解； （c）确定使用MTI/Ti超晶格的拓扑特性的人工工程的关键设计参数。在教育上，接受了该研究计划的培训的研究生获得了广泛的科学观点。通过设计拓扑量子材料的特殊课程，PI将显着扩大当代冷凝物质物理学的研究生/本科教育。该计划还扩大了代表性不足的小组的参与。该奖项反映了NSF的法定使命，并通过使用基金会的知识分子优点和更广泛的影响评估标准来评估诚实的支持。