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

非技术描述：拓扑学的数学概念研究形状的全局几何属性，例如当物体平滑变形时保持不变的空穴或表面的数量，已被应用于理解和发现固态材料中的新的电磁属性。这个项目研究了只有几个原子层厚的二维材料中的两种类型的这种现象。第一种是作为拓扑边传导主体的二维材质。在这些材料中，样品内部是绝缘的，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，它有可能被用来开发下一代节能电子器件。第二种现象发生在2D磁性材料中，其中局部磁极以旋转的方式缠绕。绕组方向可以用于信息存储，因为它们的拓扑性质使其对外部扰动具有健壮性，从而能够更长时间地保留信息。该项目进一步整合了一个教育部分，让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将开发适合所有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。演示项目为学生参与拟议的研究活动提供了一座桥梁。在教育计划中将特别鼓励和招募代表不足的群体。技术描述：原子层状材料为研究二维拓扑物理提供了丰富的平台。本项目研究了几类新的二维材料及其异质结构，以表征它们的拓扑状态，并探索操纵和设计它们的拓扑性质的新方法。第一个材料体系是最近发现的拓扑磁体MnBi2Te4，它在一种材料中结合了磁性和拓扑秩序，是几层样品中的陈氏绝缘体。这项研究的目的是表征几层样品中对拓扑有序很重要的关键性质，包括拓扑带隙和磁各向异性。第二种材料体系是基于石墨烯的莫尔异质结构，包括位于hBN上的扭曲双层石墨烯和与过渡金属二卤化物的莫尔异质结构界面的石墨烯。大周期莫尔超晶格的形成有望调制石墨烯中的朗道能级结构，这可能被用来调节石墨烯中的拓扑态。第三种材料体系是2D磁体的异质结构。这项研究探索了不同的材料组合，在界面引入强的自旋轨道耦合和破坏反转对称性，从而在磁性材料中诱导Dzyaloshinskii-Moriya相互作用并产生Skyrmions。该项目使用了几种扫描探针显微镜技术，包括微波阻抗显微镜(MIM)、静电力显微镜(EFM)和磁力显微镜(MFM)，来探测局部的电磁性质和成像真实空间中的拓扑态。本地探测器提供了传统传输技术的补充信息，可以从不同的角度对二维拓扑物理带来新的见解。这项研究的结果将为理论家改进模型参数以及材料科学家优化和改进样本质量提供重要反馈。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。

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.