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

非技术描述：物质的拓扑相因其丰富的物理性质和可能的革命性技术应用而在凝聚态物理学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了人们的极大兴趣，并且是实现新兴量子相，电子无耗散传输，自旋电子学中自旋电流的有效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。本研究项目的目标是探索三维拓扑狄拉克半金属在薄膜厚度、外电场和磁相互作用下的紧急拓扑现象。首席研究员和研究小组计划利用分子束外延技术合成具有拓扑Dirac半金属候选材料Na3Bi及其磁绝缘体异质结构的高质量外延薄膜。该研究小组计划利用运行中的纳米聚焦角分辨光谱学，在没有任何假设的情况下，直接探测导致这类量子材料新现象的复杂电子能带结构。该项目计划通过对不同实验技术、批判性思维和解决复杂研究问题的训练，支持一名研究生的博士论文。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，为期数年，来自少数民族服务机构。透过现时与少数族裔院校的合作关系，有助招收本科生。通过利用这一研究项目，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经验。此外，还计划为多元化人口制定教育举措，包括针对宾夕法尼亚州西南部少数民族中学生的外展计划。技术描述：首席研究员提出了一个综合研究项目，研究拓扑狄拉克半金属外延薄膜及其异质结构中的涌现量子现象。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、原位薄膜图图化和原位低温磁输运的实验能力，这使得研究团队能够在原始条件下合成和测量拓扑狄拉克半金属的薄膜。研究小组计划利用分子束外延获得高质量的Na3Bi外延薄膜及其磁绝缘体异质结构。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Na3Bi薄膜中厚度相关的非平凡到平凡带隙绝缘体转变、电场控制的拓扑相和t破缺拓扑态。此外，研究小组计划利用最先进的纳米聚焦操作角分辨光谱学，具有低于100纳米的空间分辨率来测量Na3Bi薄膜及其器件的费米能级依赖（使用集成静电后门）拓扑带结构。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.