Graphene-based all-proximity-coupled quantum spintronic devices

由于石墨烯独特的能带结构，可以产生两种新的拓扑量子现象：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应用提供了诱人的潜力。这两种量子现象的共同先决条件是强自旋轨道耦合，要么是本征耦合，要么是Rashba型耦合。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。虽然原生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近距离耦合来修改性能。所提出的基于量子化异常霍尔效应的量子现象可用于致密、鲁棒、低功耗和可扩展的非易失性存储器，这将大大提高当前基于磁隧道结的存储器件的性能。非易失性存储设备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建议通过参与研究项目和教授新开发的选修课程来培养本科生和研究生，特别是代表性不足的少数民族学生。PI还计划继续向STEM学校开展推广活动，为STEM高中学生指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的团队已经通过与磁性绝缘体的近距离耦合成功地证明了石墨烯中的异常霍尔效应。最近，PI的团队还通过与过渡金属二硫系材料（例如WS2）的接近效应，证明了自旋-轨道耦合的强增强。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，该器件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，很少有材料被预测到，甚至更少的材料已经被实验证明具有QSHE（例如HgTe/CdTe量子阱）和qhe（例如磁性拓扑绝缘体）。这些材料极难合成，或者只能在极低的温度下表现出所需的性能。所提出的基于石墨烯的器件是理想的系统，其中所需的相互作用可以通过邻近效应诱导。这些量子现象还没有在石墨烯中被探索过，但我希望它能显示出许多新奇有趣的特性，比如量子化输运、鲁棒霍尔电压、纯自旋电流等。如果在高温下证明这些无与伦比的特性，可能会彻底改变当今的自旋电子学。在这项研究中，PI计划展示一个基于QAHE的量子自旋电子存储设备原型。在石墨烯基器件中所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.