Graphene-based all-proximity-coupled quantum spintronic devices

由于石墨烯独特的能带结构，可能会出现两种新的量子拓扑现象：量子自旋霍尔效应(QSHE)和量子反常霍尔效应(QAHE)，这两种现象都为量子自旋电子的应用提供了诱人的潜力。这两个量子现象的一个共同前提是强的自旋-轨道耦合，无论是本征的还是拉什巴型的。在这两种现象中，QAHE需要石墨烯中额外的交换相互作用或铁磁性。尽管天然石墨烯没有相互作用，但其开放和灵活的结构允许通过与其他材料的接近耦合来改变性质。所提出的基于量子反常霍尔效应的量子现象可能被用于高密度、健壮、低功耗和可扩展的非易失性存储器，这将极大地提高现有基于磁隧道结的存储器件的性能。非易失性存储器件在现代社会中无处不在。基于量子自旋电子现象的高性能存储器件将对低功耗存储产生重大影响。PI建议通过让本科生和研究生参与研究项目并教授他们新开发的选修课来培养本科生和研究生，特别是代表不足的少数民族学生。此外，国际物理协会计划继续在一所STEM学校开展外展活动，为STEM高中生辅导科学奥林匹克竞赛项目，并在物理系主办的物理教师暑期学院期间为南加州高中的暑期物理教师讲课。Pi的团队通过与磁性绝缘体的邻近耦合，成功地证明了石墨烯中的反常霍尔效应。最近，Pi的小组还展示了通过与过渡金属二卤化物材料(例如WS2)的邻近效应来增强自旋-轨道耦合。在这项工作中，PI旨在探索全邻近耦合石墨烯器件中的诱导效应，从而在相对较高的温度下获得新的相互作用，以实现预测的量子效应。目前预测的材料很少，实验证明具有QSHE(如HgTe/CdTe量子阱)和QAHE(如磁性拓扑绝缘体)的材料更少。这些材料很难合成，或者只在极低的温度下才显示出所需的性能。所提出的基于石墨烯的设备是理想的系统，其中所需的相互作用可以通过邻近效应来诱导。这些量子现象还没有在石墨烯中被探索，但我预计它将显示许多新颖和有趣的特性，如量子化输运、稳健的霍尔电压、纯自旋电流等。这些无与伦比的特性，如果在高温下表现出来，可能会给当今的自旋电子学带来革命性的变化。在这项拟议的研究中，PI计划展示基于QAHE的量子自旋电子存储设备的原型。在基于石墨烯的设备中学到的知识将加深我们对具有可调相互作用的二维电子系统的基本理解。

Owing to graphene's unique band structure, two new topological quantum phenomena can emerge: the quantum spin Hall effect (QSHE) and the quantum anomalous Hall effect (QAHE), both offering attractive potential for quantum spintronic applications. A common prerequisite for these two quantum phenomena is strong spin-orbit coupling, either intrinsic or the Rashba type. Of the two phenomena, QAHE requires additional exchange interaction or ferromagnetism in graphene. Although native graphene has neither interaction, its open and flexible structure allows modifications of the properties by proximity coupling to other materials. The proposed quantum phenomena based on quantized anomalous Hall effect can be potentially used for dense, robust, low-power, and scalable non-volatile memory which will drastically improve the performance of the current memory devices based on magnetic tunnel junctions. The non-volatile memory devices are ubiquitous in the modern society. High-performance memory devices based on quantum spintronic phenomena will have a significant impact on low power memory. PI proposes to train the undergraduate and graduate students, especially the underrepresented minority students by engaging them with research projects and teaching them newly developed elective courses. The also PI plans to continue outreach activities to a STEM school by coaching the Science Olympiad events to STEM High school students as well as giving lectures to the summer Physics teachers from southern California high schools during Physics Teacher Summer Academy sponsored by the Physics Department. PI's group has successfully demonstrated the anomalous Hall effect in graphene via the proximity coupling with a magnetic insulator. More recently, PI's group also demonstrated a strong enhancement of spin-orbit coupling via the proximity effect with a transition metal dichalcogenide material (e.g. WS2). In this work, the PI aims to explore the induced effects in all-proximity coupled graphene devices, which acquire new interactions for realizing the predicted quantum effects at relatively high temperatures. Currently few materials are predicted and even fewer materials have been experimentally shown to exhibit QSHE (e.g. HgTe/CdTe quantum wells) and QAHE (e.g. magnetic topological insulators). These materials are extremely difficult to be synthesized or only show the desired properties at extremely low temperatures. The proposed graphene-based devices are ideal systems in which the required interactions can be induced by proximity effects. Those quantum phenomena have not yet been explored in graphene, but it I expected to show many novel and interesting properties, such as quantized transport, robust Hall voltages, pure spin current, etc. These unmatched properties, if demonstrated at high temperatures, can potentially revolutionize the present-day spin electronics. In this proposed research, the PI plans to demonstrate a prototype quantum spintronic memory device based on QAHE. The knowledge learned in the graphene-based devices will deepen our fundamental understanding of two-dimensional electron systems with tunable interactions.