CAREER: Tunable topological states in twisted van der Waals heterostructures

非技术摘要：电流通过材料的方式主要取决于其组成原子及其精确排列。例如，虽然石墨和金刚石都是由碳原子组成的，但前者是金属，而后者是电绝缘体。石墨的每个原子层都由称为石墨烯的碳原子的完美二维晶格组成。合成材料可以通过将少量石墨烯片以精确的晶格排列和扭曲角堆叠在彼此之上来创建，从而控制所有组成碳原子的排列。这些结构具有新的电子特性，这些特性由电子之间的强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，其中多片石墨烯以以前未探索的方式仔细堆叠和扭曲，并开发了实验技术来动态控制这些新型量子电子器件的性能和功能。该项目的成功可能会导致低功耗电子和量子信息的新量子技术的发展。该项目整合了教育，培训和指导的机会，为学生在快速增长的量子纳米技术领域，包括动手夏季拓展活动的高中生和研究生的研究机会。技术摘要：堆叠和扭曲原子薄的货车德瓦尔斯晶体在另一个可以导致出现的平面电子带与非平凡的拓扑结构。这些系统拥有新的相关拓扑状态的物质，可以动态调整在一个单一的设备。该项目的目标是在通过堆叠具有受控界面扭转角的单层、双层或三层石墨烯的混合匹配片组装的各种结构中发现新的相关拓扑状态。本研究利用低温电子输运，以探测由于轨道磁性和拓扑Chern绝缘体状态的出现而在这些结构中产生的量子异常霍尔效应。此外，该项目采用了静水压力，静电屏蔽和电场调谐的组合，以实现动态控制的陈数-量化的拓扑不变量表征系统。开发具有大且可调的陈氏数的新陈氏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，本科和研究生在量子纳米电子学的最先进的技术状态。这个奖项反映了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 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.