石墨烯-二维磁性半导体异质结的电学输运性质研究

Graphene is proposed to be an ideal material for ultra-high density spintronic devices, as its mobility is excellent and the spin relaxation length is extraordinary long. However, without intrinsic magnetism, graphene cannot be used to produce and detect the spin information in devices. Moreover, it prevents the investigation of some interesting edge states in graphene, such as Quantum Anomalous Hall Effect. From previous studies, we found that proximity effect can change the property of one material while keep its high quality. For example, we successfully enhanced the spin-orbit interactions in graphene through WS2 substrates. Recently our research focused on the magnetic two dimensional (2D) materials, such as CrI3 and Fe3TeGe2, and we already get deep understanding about these materials. So we propose to introduce magnetism into high quality graphene through proximity effect from 2D magnetic materials substrates. We plan to fabricate van der Waals heterostructure of graphene and 2D magnetic semiconductors, such as hBN/CrI3/graphene/hBN, then detect the introduced magnetism through electronic transport measurements, and finally explain the experimental data with the help of theoretical calculations. This project will open possible new routes in graphene spintronics and to access topological states in graphene based systems.

由于优异的高迁移率和长自旋弛豫时间等特性，石墨烯在高密度自旋电子器件等领域具有巨大的应用潜力。在保持石墨烯良好特性的同时有效引入磁性，并探索其自旋电子学机制以及应用和由此衍生的新奇拓扑态是相关新兴领域的前沿热点和难点问题。基于前期对CrI3、Fe3GeTe2等二维磁性材料和WS2诱导石墨烯自旋轨道耦合增强等科研实践的深厚积累，本项目提出采用二维磁性半导体作为衬底，通过构建hBN/CrI3/石墨烯/hBN等石墨烯-二维磁性半导体异质结，在保持石墨烯自身优异的电学特性的前提下基于近邻效应引入系统本征磁性。本项目拟应用反常霍尔效应等低温电学输运性质实验测量与第一性原理计算相结合的方式表征和深入分析石墨烯-二维磁性半导体异质结的电学输运性质，在相关领域取得一批开拓性科研成果，为石墨烯在自旋电子学应用、新奇拓扑态等前沿研究方向提供理论基础和应用指导。

二维材料由于表面无悬挂键、层间通过范德瓦尔斯力耦合，因此易于构建界面原子级平整的异质结，从而有利于通过构建异质结来改变材料性质、实现特定功能。本项目主要通过构建不同类型的石墨烯-二维磁性半导体异质结，利用电学输运性质的测量与分析研究二维磁性半导体的性质及其对石墨烯能带的影响。研究获得的主要进展如下:(1) 以不同的二维磁性半导体CrX3(X=Cl,Br,I)为衬底制备”双层石墨烯/CrX3”异质结，发现石墨烯向三卤化铬转移的电子浓度高达 10^13 cm^-2, 因此在界面处产生了非常大的内建电场，从而致使双层石墨烯打开了超过 100 meV的能隙。然而反常霍尔效应等测量并未发现石墨烯中有明显的铁磁性。系列实验数据分析与第一性原理计算完美符合，相关成果为调控石墨烯能带结构提供了新方法。(2) 成功制备了“石墨烯-CrBr3-石墨烯”异质结，实验发现其隧穿电导对磁场(H)及温度(T)的依赖完全是由磁化强度 M(H, T) 所决定。理论分析这一现象来源于铁磁半导体CrBr3中能带自旋劈裂的大小与M 成正比。这一结果为理解磁性半导体电子隧穿过程提供了新视角，也为通过电子隧穿来探测铁磁半导体的磁学性质提供了有效方案。在本项目的资助下，共发表SCI论文4篇，包括本项目为第一标注的Nature Communications一篇。