基于石墨烯的量子反常霍尔效应探索

The quantum anomalous Hall effect (QAHE) predicted recently by theoretical studies originates from the internal magnetization and strong spin-orbital coupling. QAHE can be regarded as quantum Hall effect without applied magnetic field, i.e., there exist dissipationless current at the edges, whose direction is topologically protected without disorder-induced backscattering. Nevertheless, the experimental realization of QAHE is still a big challenge. In this project, we will prepare graphene samples by various methods, and further enhance the spin-orbital coupling and break the time-reversal symmetry by decoration with 3d/5d atoms or putting the graphene on ferromagnetic insulators (such as EuO). Then we will study the adsorption configuration of the adsorbed atoms, magnetism, induced bulk bandgap, as well as edge states by scanning tunneling microscopy. We will measure the longitudinal resistance and Hall effect by transport, to determine some parameters of such electronic systems. We will explore to manipulate the bandgap and the anomalous Hall effect by tuning the doping concentration and gate voltage. Based on these studies, we will try to optimize the growth parameters to enhance the anomalous Hall effect to approach the QAHE. The QAHE realization will not only deepen our understanding of the topological quantum theory in condensed matter physics, but also will help to develop the novel quantum devices and quantum computing with low energy consumption.

最近理论预言的量子反常霍尔效应源于内在的磁化强度以及强自旋轨道耦合，可看作无需外磁场的量子霍尔效应，即在零磁场下具有边缘电荷流，其行进方向受拓扑保护，不存在杂质势场引起的背散射。但迄今为止量子反常霍尔效应的实验实现还有很大挑战。本项目拟通过各种方法制备石墨烯，然后在石墨烯上进行3d和5d重金属原子掺杂或者将石墨烯置于EuO磁性绝缘衬底上，以增强其自旋轨道耦合以及破坏其时间反演对称性。利用扫描隧道显微术对吸附结构、磁性、诱导体能隙以及边缘态进行研究；利用低温强磁场输运手段对其纵向电阻和霍尔效应进行表征，确定此电子体系的一些参数。探索掺杂浓度、栅压等因素对诱导体能隙以及反常霍尔效应的调控。进一步优化制备条件，增强反常霍尔效应，力争实现量子反常霍尔效应。量子反常霍尔效应的实验实现不仅将深化人们对凝聚态拓扑量子理论的理解，还将极大推动低能耗的新型量子器件和量子计算的发展。

探索和调控石墨烯的量子效应（例如量子反常霍尔效应、量子相干、量子等离激元等）对设计基于石墨烯的新型量子器件具有重要意义。我们在相关领域取得了若干进展：（1）观察到石墨烯在反铁磁绝缘衬底LaMnO3近邻下的非线性霍尔效应，以及在铁磁绝缘薄膜EuS近邻下迁移率的极大提高，为实现石墨烯的量子反常霍尔效应提供了重要线索。（2）实现了石墨烯等离激元激发和传播的量子调控，发现电子-等离激元耦合对石墨烯电子的量子相干性的极大增强效应。（3）利用分子一维受限反应制备最窄石墨烯条带并预言其自旋开关效应。（4）利用光栅压实现了石墨烯的可控双极性掺杂并构筑了石墨烯电子超晶格，观察到石墨烯在LaAlO3/SrTiO3近邻下的巨大光电导并设计新概念深紫外探测器。在该项目执行期间，共发表SCI论文19篇，包括3篇Phys. Rev. Lett.，1篇Adv. Mater.，1篇Nat. Commun.和3篇Nano Lett.。培养6名博士生毕业，2名硕士生毕业，1名博士后出站。