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

非技术描述：物质的拓扑相由于其丰富的物理学和可能的革命性技术应用，在凝聚态物理学中引起了极大的关注。三维拓扑Dirac半金属材料由于其有趣的电子能带结构引起了人们的极大兴趣，是实现量子涌现相、电子的无耗散传输、自旋电子学的高效自旋电流产生以及拓扑场效应晶体管等先进量子器件概念的理想平台。本研究项目的目的是探索由薄膜厚度、外加电场和磁场相互作用调节的三维拓扑Dirac半金属中出现的拓扑现象。首席研究人员和研究团队计划使用分子束外延技术合成高质量的Dirac半金属候选化合物Na3Bi及其带有磁性绝缘体的异质结构的外延薄膜。利用操作中纳米聚焦角度分辨光电子能谱，研究小组计划在没有假设的情况下直接探索复杂的电子能带结构，这种结构最终导致这类量子材料中的新现象。该项目计划通过培训不同的实验技术、批判性思维和解决复杂的研究问题来支持研究生的博士论文。这位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，在一家少数族裔服务机构工作多年。通过与少数族裔服务机构的现有合作，促进了本科生的招生。通过利用这一研究计划，首席研究员建议设计和实施一门新的高级实验课程，为学生提供研究级设备的动手实验体验。此外，计划为多样化人口制定教育倡议，包括针对宾夕法尼亚州西南部代表不足的少数族裔的初中生和高中生的外联计划。技术描述：主要研究人员提出了一个全面的研究项目，以研究拓扑Dirac半金属及其异质结构外延薄膜中的量子现象。这项研究是由一个独特的自制超高真空团簇系统实现的，该系统包括分子束外延、原位薄膜构图和原位低温磁传输的实验能力，使研究团队能够在原始条件下合成和测量拓扑结构的狄拉克半金属薄膜。该研究小组计划利用分子束外延获得高质量的Na3Bi及其具有磁性绝缘体的异质结薄膜。该研究小组计划使用量子输运测量来研究厚度相关的非平凡带隙绝缘体到平凡带隙绝缘体的转变、电场控制的拓扑相以及集成了顶部和底部静电门的Na3Bi薄膜中的T-破缺拓扑态。此外，研究团队计划利用最先进的纳米聚焦、低于100 nm空间分辨率的操作角分辨光电子能谱来测量Na3Bi薄膜及其器件的费米能级依赖(使用集成静电后门)拓扑能带结构。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.