Graphene-based all-proximity-coupled quantum spintronic devices

点击翻译按钮获取中文摘要

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.