CAREER: Emergent quantum phenomena in epitaxial thin films of topological Dirac semimetal and its heterostructures

非技术性描述：物质的拓扑相由于其丰富的物理和可能的革命性技术应用而在凝聚态物理中引起了极大的关注。三维拓扑狄拉克半金属由于其有趣的电子能带结构而引起人们极大的兴趣，并且是实现涌现量子相位、电子的无耗散传输、自旋电子学的自旋电流的有效产生以及诸如拓扑场效应晶体管的先进量子器件概念的理想平台。本研究计划的目的是探讨三维拓扑狄拉克半金属中的新兴拓扑现象，这些拓扑现象由膜厚度、外部电场和磁相互作用所调谐。主要研究者和研究团队计划使用分子束外延合成拓扑狄拉克半金属候选物Na 3Bi及其具有磁性绝缘体的异质结构的高质量外延薄膜。采用在操作纳米聚焦角分辨光电子能谱，研究小组计划直接探测，没有假设，复杂的电子能带结构，最终负责这类量子材料中的新现象。该项目计划通过不同的实验技术，批判性思维和解决复杂研究问题的培训来支持研究生的博士论文。首席研究员还计划每年夏天在她的实验室为本科生提供研究经验，从少数民族服务机构多年。通过与少数民族服务机构的现有联系，促进了本科生的招聘。通过利用这个研究项目，主要研究者建议设计和实施一个新的先进的实验室课程，为学生提供动手实验室的经验，研究级设备。此外，计划为多样化的人口制定教育举措，包括针对宾夕法尼亚州西南部代表性不足的少数民族的初中和高中学生的外展方案。 技术简介：主要研究者提出了一个全面的研究项目，研究拓扑狄拉克半金属及其异质结构的外延薄膜中出现的量子现象。这项研究是由一个独特的自制的真空簇系统，包括分子束外延，原位薄膜图案化和原位低温磁输运的实验能力，使研究小组能够合成和测量拓扑狄拉克半金属薄膜在原始条件下。研究小组计划利用分子束外延获得高质量的Na 3Bi外延薄膜及其具有磁性绝缘体的异质结构。研究小组计划采用量子输运测量来研究具有集成顶部和底部静电门的Na 3Bi薄膜中的厚度依赖的非平凡到平凡的带隙绝缘体转变，电场控制的拓扑相和T-破缺拓扑态。此外，本发明还提供了一种方法，该研究小组计划利用最先进的纳米聚焦的角度分辨光电子能谱技术，以低于100纳米的空间分辨率来测量费米能级依赖的（使用集成静电背栅）该奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的知识产权评估的支持。优点和更广泛的影响审查标准。

Nontechnical description:Topological phases of matter have attracted great attention in condensed matter physics due to their rich physics and possible revolutionary technological applications. Three-dimensional topological Dirac semimetals are of great interest due to their intriguing electronic band structure and are an ideal platform to realize emergent quantum phases, dissipationless transmission of electrons, efficient generation of spin current for spintronics, and advanced quantum device concepts such as the topological field effect transistor. The goal of this research project is to explore emergent topological phenomena in a three-dimensional topological Dirac semimetal as tuned by film thickness, external electric field, and magnetic interactions. The principal investigator and research team plans to synthesize high quality epitaxial thin films of a topological Dirac semimetal candidate, Na3Bi, and its heterostructures with magnetic insulators using molecular beam epitaxy. Employing in-operando nano-focused angle-resolved photoemission spectroscopy, the research team plans to directly probe, with no assumptions, the complex electronic band structure that is ultimately responsible for novel phenomena in this class of quantum materials. This project plans to support the doctorate dissertation of a graduate student, through training on different experimental techniques, critical thinking and solving complex research problems. The principal investigator also plans to provide research experience for undergraduate students in her lab every summer, for multiple years from a minority serving institution. The recruitment of the undergraduate students is facilitated through the existing tie-ups with the minority serving institutions. By taking advantage of this research program, the principal investigator proposes to design and implement a new advanced lab course to provide hands-on lab experience to students on research-grade equipment. Also, the plans to develop educational initiatives for a diverse population including an outreach program targeted towards middle and high school students belonging to underrepresented minorities in southwestern Pennsylvania. Technical description:The principal investigator proposes a comprehensive research project to study emergent quantum phenomena in epitaxial thin films of a topological Dirac semimetal and its heterostructures. This research is enabled by a unique home-built ultrahigh vacuum cluster system comprising of experimental capabilities of molecular beam epitaxy, in-situ thin film patterning, and in-situ cryogenic magnetotransport, which allows the research team to synthesize and measure thin films of a topological Dirac semimetal in pristine conditions. The research team plans to utilize molecular beam epitaxy to obtain high quality epitaxial thin films of Na3Bi and its heterostructures with magnetic insulators. The research team plans to employ quantum transport measurements to study thickness dependent non-trivial to trivial band gap insulator transitions, electric field controlled topological phases, and T-broken topological states in thin films of Na3Bi with integrated top and bottom electrostatic gates. In addition, the research team plans to utilize a state-of-the-art nano-focused in-operando angle-resolved photoemission spectroscopy with sub-100 nm spatial resolution to measure the Fermi level dependent (using integrated electrostatic back gate) topological band structure of Na3Bi thin films and their devices.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.