Visualizing Novel Electronic Orders in Bilayer Graphene Systems

摘要：量子材料在建立技术的未来中起着关键作用。基于单原子厚度材料（如石墨烯）及其堆叠的发现和研究进展为探索电子现象创造了一个新的舞台，在这个舞台上，电子之间的相互作用可以用扫描隧道显微镜（STM）等现代技术来控制和分析。本研究项目的重点是可视化材料中的量子现象，这些材料的电子密度由磁场的应用或层间相对扭曲控制。通过将成像电子态的力量引入研究这些令人兴奋的材料，该项目揭示了这些量子态形成的微观机制及其性质。该项目培养的研究生和本科生将构成未来学术界和工业界量子科学与技术的劳动力。这项研究还补充了一项教育议程，即普林斯顿大学的本科课程“未来领导者的物理学”的持续改进，该课程向有兴趣在政府和政策领域担任领导角色的非科学专业学生介绍物理学（从基础知识到量子现象）。技术摘要：本项目主要研究新型二维材料中的电子相，其中电子相关是由占据平坦带的电子引起的。研究小组利用扫描隧道显微镜（STM）的原子尺度成像和光谱学，以独特的方式探索了平面带中电子的广泛量子现象。从这些实验中获得的信息几乎是不可能从其他类型的宏观平均方法中获得的，因此将为电子相互作用相的研究增加一个重要的新视角。在超干净的设备中，具有复杂破缺对称性和有序的新量子相正在被创造出来，它们形成背后的复杂相关性正在被探索。具有分馏电荷的奇异电子相可能承载非阿贝尔任意子，是研究的焦点。特别是，该项目支持检测双层石墨烯中的分数量子霍尔相（FQH），并检测用STM局部探测这些态的方法。该系统还提供了一个独特的设置，可以可视化场致Wigner晶体、电子的气泡和条纹相以及它们与FQH相的竞争。另一个正在探索的平带系统是魔角扭曲双层石墨烯，其中STM测量用于了解在该系统中产生相关绝缘体和拓扑绝缘体的破缺对称性状态的性质。局部STM成像及其分析被用来表征破缺对称性，并研究应变、扭转角和减法氮化硼对其的影响。几个基于扫描隧道显微镜的新实验技术也在这个项目中开发。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。

Non-technical Abstract: Quantum materials play a key role in establishing the future of technology. The discovery of and research advances based on single-atom-thick materials, such as graphene, and their stacks is creating a new arena for exploration of electronic phenomena in which interaction between electrons can be controlled and analyzed with modern techniques such as the scanning tunneling microscopy (STM). This research project is focused on visualization of quantum phenomena in materials with density of electrons controlled by application of a magnetic field or twisting of layers relative to each other. By bringing the power of imaging electronic states to study these exciting materials, this project reveals the microscopic mechanism by which these quantum states are formed and their properties. The graduate and undergraduate students trained in this project will constitute the future workforce for quantum science and technology in academia and industry. This research is supplemented with an educational agenda, the continued improvement of a Princeton undergraduate course “Physics for Future Leaders”, that introduces physics (from basics to quantum phenomena) to non-science majors who are interested in pursuing leadership roles in government and policy arenas.Technical Abstract: This project is focused on electronic phases in novel two dimensional materials in which electronic correlation is induced by electrons occupying a flat band. The research team explores a wide range of quantum phenomena for electrons in flat bands in unique ways using atomic scale imaging and spectroscopy with the scanning tunneling microscope (STM). The information obtained from these experiments is nearly impossible to obtain from other types of macroscopically averaged methods and hence will add an important new perspective to the study of interacting phases of electrons. New quantum phases with complex broken symmetry and ordering are being created in ultra clean devices and the complex correlations underlying their formation is being explored. Exotic electronic phases with fractionalized charges that may host non-abelian anyons are the focus of investigation. In particular, the project supports examination of fractional quantum Hall phases (FQH) in bilayer graphene, examining ways in which such states can be probed locally with the STM. This system also provides a unique setting to visualize field-induced Wigner crystals, bubble and stripe phases of electrons and their competition with FQH phases. Another flat band system being explored is that of magic-angle twisted bilayer graphene in which STM measurements are used to understand the nature of broken symmetry states that give rise to correlated and topological insulators found in this system. Local STM imaging and its analysis are being used to characterize broken symmetries and to study the influence of strain, twist angle, and alignment with subtracted boron-nitride. Several new experimental techniques based on scanning tunneling microscopy is also being developed in this program.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.