CAREER: Tunable topological states in twisted van der Waals heterostructures

非技术摘要：电流在材料中流动的方式主要取决于其组成原子及其精确排列。例如，虽然石墨和钻石都是纯碳原子组成的，但前者是金属，而后者是电绝缘体。石墨的每一层原子层都由一种叫做石墨烯的完美的二维碳原子晶格组成。合成材料可以通过将少量具有精确晶格排列和扭曲角度的石墨烯片层堆叠在一起来创建，从而控制所有组成碳原子的排列。这些结构具有新颖的电子性质，这些性质由电子之间的强烈相互作用和其他量子力学效应主导。该项目研究了新的器件架构，其中多张石墨烯以以前未被探索的方式小心地堆叠和扭曲，并另外开发了实验技术来动态控制这些新型量子电子器件的性质和功能。该项目的成功可能会导致用于低功率电子和量子信息的新量子技术的发展。该项目整合了在快速发展的量子纳米技术领域为学生提供的教育、培训和指导机会，包括为高中生提供的暑期实践推广活动，以及为本科生和研究生提供的研究机会。技术摘要：将原子薄的范德华晶体堆叠和扭曲在彼此之上可以导致具有不平凡拓扑结构的扁平电子频带的出现。这些系统拥有新的相关物质拓扑状态，可以在单个设备内动态调整。这个项目的目标是在一类结构中发现新的相关拓扑状态，这些结构是通过堆叠混合和匹配的单层、双层或三层石墨烯薄片并控制界面扭曲角而组装的。本研究利用低温电子输运来探索这些结构中由于轨道磁性和拓扑陈绝缘态的出现而产生的量子反常霍尔效应。此外，该方案采用了静压、静电屏蔽和电场调节相结合的方法，以实现对表征系统的量化拓扑不变量-陈数的动态控制。开发具有大的可调陈数的新型陈绝缘体，为创造具有无耗散电荷传输的未来节能设备以及潜在的量子计算应用提供了机会。该研究项目和相关的推广活动培训了广泛的高中生、本科生和研究生，了解量子纳米电子的最新技术。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 Abstract:The way in which electricity flows through a material depends critically on its constituent atoms and their precise arrangement. For example, although graphite and diamond are both composed purely of carbon atoms, the former is a metal whereas the latter is an electrical insulator. Each atomic layer of graphite consists of a perfect two-dimensional lattice of carbon atoms called graphene. Synthetic materials can be created by stacking a small number of graphene sheets atop one another with precise lattice alignments and twist angles, thereby controlling the arrangement of all of the constituent carbon atoms. These structures host novel electronic properties that are dominated by strong interactions amongst the electrons and other quantum mechanical effects. This project investigates new device architectures in which multiple sheets of graphene are carefully stacked and twisted in previously unexplored ways, and additionally develops experimental techniques to dynamically control the properties and functionality of these novel quantum electronic devices. The success of this project may lead to the development of new quantum technologies for low-power electronics and quantum information. The project integrates educational, training, and mentoring opportunities for students in the rapidly growing field of quantum nanotechnology, including a hands-on summer outreach activity for high school students and research opportunities for undergraduate and graduate students.Technical Abstract:Stacking and twisting atomically thin van der Waals crystals atop one another can lead to the emergence of flat electronic bands with nontrivial topology. These systems host novel correlated topological states of matter that can be dynamically tuned within a single device. The objective of this project is to discover new correlated topological states in an assortment of structures assembled by stacking mixed-and-matched sheets of monolayer, bilayer, or trilayer graphene with controlled interfacial twist angles. This research utilizes low-temperature electronic transport in order to probe the quantum anomalous Hall effect that arises in these structures owing to the emergence of orbital magnetism and topological Chern insulator states. Furthermore, this project employs a combination of hydrostatic pressure, electrostatic screening, and electric field tuning in order to achieve dynamic control of the Chern number – the quantized topological invariant characterizing the system. Developing new Chern insulators with large and tunable Chern number presents opportunities for creating future energy-efficient devices with dissipationless charge transport, as well as for potential quantum computing applications. The research project and associated outreach activities train a broad range of high school, undergraduate, and graduate students in state of the art techniques in quantum nanoelectronics.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.