CAREER: Study of Electronic and Magnetic Topological Phenomena in Two Dimensional Quantum Materials with Scanning Probe Microscopy

非技术性说明：拓扑学的数学概念研究形状的整体几何性质，如物体平滑变形时保持不变的孔或表面的数量，已被用于理解和发现固态材料中新的电子和磁性。该项目研究两种类型的这种现象在二维材料，只有几个原子层厚。第一种是承载拓扑边传导的2D材质。在这些材料中，样品的内部是绝缘的，而电流只能沿着边缘流动。这种边缘导电可以大大减少电流流动过程中的能量损失，因此，它有可能用于开发下一代节能电子设备。第二种类型的现象发生在2D磁性材料中，其中局部磁极以涡旋模式缠绕。缠绕方向可以用于信息存储，因为它们的拓扑性质使它们对外部扰动具有鲁棒性，从而能够更长时间地保留信息。该项目进一步整合了教育部分，使本科生和高中生参与量子材料和纳米技术领域的多学科研究。PI将开发适合各个级别学生的研究模块，例如构建涉及硬件设计和电子开发的演示纳米表征工具。示范项目为学生参与拟议的研究活动提供了一个桥梁。技术描述：原子层状材料为二维拓扑物理的研究提供了一个丰富的平台。该项目研究了几种新型二维材料及其异质结构，以表征其拓扑状态，并探索操纵和设计其拓扑特性的新方法。第一个材料系统是最近发现的拓扑磁体MnBi 2 Te 4，它将磁性和拓扑有序结合在一种材料中，并且在几层样品中是陈氏绝缘体。拟议的研究旨在表征几层样品中对拓扑顺序很重要的关键属性，包括拓扑间隙和磁各向异性。第二材料系统是基于石墨烯的莫尔异质结构，包括在hBN上排列的扭曲双层石墨烯和与过渡金属二硫属化物的莫尔异质结构接合的石墨烯。具有大周期性的莫尔超晶格的形成有望调制石墨烯中的朗道能级结构，这可能潜在地用于调谐石墨烯中的拓扑状态。第三种材料系统是2D磁体的异质结构。拟议的研究探索了不同的材料组合，以在界面处引入强自旋轨道耦合并打破反转对称性，这可能会诱导Dzyaloshinskiii-Moriya相互作用并在磁性材料中创建skyrmions。本计画利用微波阻抗显微镜、静电力显微镜、磁力显微镜等扫描探针显微镜技术，来探测局域的电磁性质，并在真实的空间中对拓扑态进行成像。局域探测为传统的输运技术提供了补充信息，可以从不同的角度为二维拓扑物理学带来新的见解。这项研究的结果将为理论家提供重要的反馈，以完善模型参数，并为材料科学家，以优化和提高样品quality.This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智力价值和更广泛的影响审查标准进行评估的支持。

Non-technical description:The mathematical concept of topology, which studies global geometrical properties of shapes, such as the number of holes or surfaces, that remain unchanged when the objects are smoothly deformed, has been applied to understand and discover novel electronic and magnetic properties in solid state materials. This project studies two types of such phenomena in two-dimensional materials that are only a few atomic layers thick. The first is 2D materials that host topological edge conduction. In these materials, the interior of sample is insulating while electrical current can only flow along the edges. This kind of edge conduction can greatly reduce the energy loss during the current flow, therefore, it can potentially be used to develop next generation of energy efficient electronic devices. The second type of phenomena occurs in 2D magnetic materials where the local magnetic poles wind around in a swirling pattern. The winding directions can be used for information storage as their topological properties make them robust against external perturbation thus capable of retaining information for longer time. This project further integrates an education component to engage both undergraduate and high school students in multidisciplinary research in the field of quantum materials and nanotechnology. The PI will develop research modules that are suitable for students at all levels such as building demo nano characterization tools that involve both hardware design and electronics development. The demo projects provide a bridge for the students to participate in the proposed research activities. Under-represented groups will be particularly encouraged and recruited in the education programs.Technical description:Atomic layered materials provide a rich platform to study topological physics in two dimensions. This project investigates several families of novel 2D materials and their heterostructures to characterize their topological states and explore new methods to manipulate and engineer their topological properties. The first material system is the recently discovered topological magnet, MnBi2Te4, which combines magnetism and topological order in one material and is a Chern insulator in few-layer samples. The proposed research aims to characterize key properties in few-layer samples that are important for the topological order, including the topological gap and the magnetic anisotropy. The second material system is graphene based moiré heterostructures, including twisted bilayer graphene aligned on hBN and graphene interfaced with moiré heterostructures of transition metal dichalcogenides. The formation of moiré superlattice with a large periodicity is expected to modulate the Landau level structures in graphene, which could potentially be used to tune the topological states in graphene. The third material system is heterostructures of 2D magnets. The proposed research explores different material combinations to introduce strong spin orbit coupling and break inversion symmetry at the interface which could induce the Dzyaloshinskii–Moriya interaction and create skyrmions in the magnetic materials. This project employs several scanning probe microscopy techniques, including microwave impedance microscopy (MIM), electrostatic force microscopy (EFM), and magnetic force microscopy (MFM), to probe the local electronic and magnetic properties and image the topological states in real space. The local probes provide complementary information to conventional transport techniques, which can bring in new insights on topological physics in two dimensions from a different perspective. Results from this research will provide important feedback for theorists to refine model parameters and for material scientist to optimize and improve sample qualities.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.