基于范德华异质结的新型自旋操控

The effective field is an important mechanism to realize spin manipulation in spintronics. Rashba field induced by spin orbital coupling (SOC) at the interface is the most common effective field. For example, in the monolayer transition metal dichalcogenides (TMDs) system, the direction of Rashba field is in-plane and perpendicular to the direction of the electron motion. However, It’s noteworthy that the SOC in the TMDs will also split the valley, causing a out-of-plane Zeeman-type effective field, which is independent on the direction of electron motion, and hundreds of tesla. The ability of Zeeman field in spin manipulation has not been revealed yet, and its complementarity with the characteristics of Rashba field indicates new spin manipulation mechanisms. In view of this, based on previous studies involving heterojunction and magnetic tunnel junction of two-dimensional material, we plan to choose van der Waals (vdW) heterojunction of TMDs and two-dimensional ferromagnetic material. And firstly, we will realize the magnetization switching of two-dimensional ferromagnetic materials by Rashba field at room temperature. Then based on the double-gate structure, the Zeeman field and Rashba field will be simultaneously adjusted, and the mechanism of spin manipulation by Zeeman field will be studied. After understanding the spin manipulation cooperativity by the Zeeman and Rashba field, A programmable spin memory device based on vdW magnetic tunneling junction will be constructed. This work will contribute to the realization of the Spin-Orbital-Torque switching of the two-dimensional system, and reveal the new spin control mechanism beyond Rashba, which is of great significance to the research of new methods, new effects, new mechanisms and new devices in spintronics.

有效场在自旋电子学中是实现自旋操控的重要机制。自旋轨道耦合(SOC)在界面引起的Rashba(R)场是最常见的有效场。例如在单层过渡金属硫族化合物TMDs体系中，R场方向位于材料面内，且与电子运动方向垂直。然而我们注意到，TMDs体系中SOC还会使能谷发生劈裂，引起一个方向在面外的Zeeman(Z)有效场，其与电子运动方向无关，可达百特斯拉。但Z场在自旋操控方面的能力目前还未被揭示，其与R场各个特征的互补性则预示着全新的自旋操控机制。鉴于此，我们基于前期二维材料异质结及磁隧道结的研究，拟基于TMDs与二维铁磁材料的范德瓦尔兹（vdW）异质结体系，利用R场实现室温二维铁磁电流驱动磁翻转。并基于双栅结构，同时实现对Z、R场的独立调节，研究Z场对自旋的操控机制。在阐明Z、R场协同操控自旋的机制基础上，构建基于vdW磁隧道结的可编程自旋存储器件。此工作将为自旋操控给出新思路、新机制和新器件。

本项目围绕“基于范德华异质结的新型自旋操控”的主题，针对电子色散能谷 Zeeman型有效场对自旋输运的作用这一基本科学问题，利用二维 TMDs 材料和二维铁磁材料构建全二维范德华异质结，通过独辟蹊径的调控和测量手段，探索实现新型自旋操控机制：1）我们发展了“活字转移”实现了二维材料的批量化灵活转移堆垛，可以精确地控制二维材料的位置和方向，界面的高洁净度使我们实现了同类器件中最高的磁阻结果。2）我们发明了自旋输运沟道的相量检测来提取本征自旋物理过程，演示了这个方法可以用来揭示自旋输运沟通的自旋弛豫机理和门控可调谐性，通过频率调节界面阻抗，可以有效消除检测电极的自旋回流，使自旋极化率提高33%。据此，我们提出了一种灵活解决电导与相位失配的策略，可使自旋信号提高10倍。3）我们在实验上澄清二维材料自旋阀信号争议，为二维自旋电子学中模糊甚至矛盾的信号提供了明晰的分析框架，这不仅有助于理清复杂的基本特征，而且对改进二维自旋电子学的应用具有重要意义。4）我们利用垂直自旋阀的磁电阻揭示了巨valley-Zeeman场下的平面内自旋动力学，我们利用WSe2的层数、叠加相位以及栅电压等方法，证明了valley-Zeeman SOF诱导的自旋翻转的可调谐性，为有效控制自旋输运提供了新的策略，将自旋晶体管沟道长度由微米一举缩短至亚纳米，在高密度和超低功率自旋电子器件中具有广阔的应用前景。5）我们研究了VSe2二维铁磁隧道结偏压驱动的自旋输运特性。利用密度泛函理论结合非平衡态格林函数方法，发现了高达5600%的隧道磁电阻。以上成果发表应用物理旗舰期刊Applied Physics Reviews （IF=19.5）封面文章1篇；并美国物理联合会AIP撰文推荐，发表国内顶级期刊 Nanoscale（ESI高被引）1篇；以及发表领域知名期刊IEEE TED 等。