Visualizing Novel Electronic Orders in Bilayer Graphene Systems

非技术摘要：量子材料在确定技术的未来方面发挥着关键作用。单原子厚度材料(如石墨烯)及其堆栈的发现和研究进展为探索电子现象创造了一个新的平台，其中电子之间的相互作用可以通过扫描隧道显微镜(STM)等现代技术进行控制和分析。这项研究项目集中在通过施加磁场或相互扭曲的层来控制电子密度的材料中的量子现象的可视化。通过将成像电子态的能力引入到对这些激发材料的研究中，这个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成为未来学术界和工业界量子科学和技术的劳动力。这项研究还补充了一项教育议程，这是普林斯顿大学本科课程“未来领导者的物理学”的继续改进，该课程向有兴趣在政府和政策领域担任领导角色的非理科专业的学生介绍物理学(从基础到量子现象)。技术摘要：该项目专注于新型二维材料中的电子相，其中电子相关是由占据平带的电子引起的。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带电子的一系列量子现象。从这些实验中获得的信息几乎不可能从其他类型的宏观平均方法中获得，因此将为电子相互作用相的研究增加一个重要的新视角。具有复杂破坏对称性和有序性的新量子相正在超清洁设备中被创造出来，其形成背后的复杂关联正在被探索中。可能含有非阿贝尔任意子的带有分馏电荷的奇异电子相是研究的重点。特别是，该项目支持对双层石墨烯中的分数量子霍尔相(FQH)的检查，检查可以使用STM局部探测此类状态的方法。该系统还提供了一个独特的设置来可视化场诱导的维格纳晶体，电子的泡状和条状相以及它们与FQH相的竞争。另一个正在探索的平带系统是魔角扭曲的双层石墨烯系统，其中STM测量被用来了解在该系统中发现的关联和拓扑绝缘体的破坏对称态的性质。局部扫描隧道显微镜成像及其分析被用来表征破坏的对称性，并研究应变、扭角和与减去的氮化硼对齐的影响。该计划还开发了几项基于扫描隧道显微镜的新实验技术。这一奖项反映了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。

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.