基于人工二维晶格的铁磁金属量子输运性质研究

Due to unique symmetry and the reduced dimensionality, low-dimensional materials possess many novel and peculiar properties, especially the spin related quantum transport, which has aroused wide concern among the people. Focus on these pioneer fields, the quantum transport properties of ferromagnetic metal on two-dimensional Au lattices would be researched in this project. First, the first-principle simulations based on the density-functional theory will be employed to calculate the the stable atomic structure and spin electronic structures of ferromagnetic metal (Fe, Co, Ni) quantum dot. Which enable us to understand the interaction between the quantum dot and two-dimensional Au lattices. In experiments, large-scale two-dimensional Au lattices were fabricated by MBE technology, the ferromagnetic metal atoms will then be deposited onto the two-dimensional Au lattices. The quantum dot/quantum dots array of ferromagnetic metal would be fabricated at the corner hole sites（relative to Si(111)-7x7 substrate）of two-dimensional Au lattices by optimization the growth and anneal conditions. The topography of quantum dot and the structures of spintronic electronic states, as well as the spatial distribution will be characterized in an atomic resolution by the spin polarized scanning tunneling microscopy under certain temperature and magnetic fields condition. And the quantum state coupling and spin-orbit coupling effects of the system would be explored. By further employing of the unique double-probe STM/STS technique, the quantum transport properties of the system，which is angle-dependent and distance-dependent, will be detected under the modulation of periodic potentials induced by two-dimensional Au lattices. And the microphysical mechanism of novel quantum transport properties would be explores in great depth， which would enable us to the achievements of the effective control of the quantum transport behaviors.

低维结构材料因其独特的对称性和缺失的维度具有诸多新奇的物理性质，尤其与自旋相关的量子输运已引起人们的广泛关注。本项目围绕这一前沿热点，开展铁磁金属量子输运性质研究。首先拟从第一性原理入手，计算零维铁磁金属（Fe、Co、Ni）量子点的稳定构型和自旋电子结构。实验上，采用MBE技术，制备大尺度二维Au晶格，并通过优化生长及退火条件，在二维Au晶格角洞位置（相对于Si（111）-7x7衬底）构筑铁磁金属量子点/量子点阵列。利用自旋极化扫描隧道显微技术，表征不同温度、磁场条件下量子点的表面形貌、自旋电子态及其空间分布，探索体系的量子态耦合以及自旋轨道耦合效应。进一步采用独特的双探针扫描隧道显微技术，实现二维Au晶格周期势场调控下体系角度分辨、路径分辨的量子输运性质表征，深入探索量子输运特性的微观物理机制，进而实现对其量子输运行为的人为有效调控。

二维材料因其独特的对称性和缺失的维度具有诸多新奇的物理性质，尤其与输运、自旋等相关的课题已成为科学研究的前沿热点。本项目采用理论模拟结合实验的方法对本课题作深入的探讨。首先，通过第一性原理密度泛函理论,系统地研究了单层GaSe表面Fe原子吸附体系的几何结构及自旋电子特性。计算发现，Fe单原子吸附的Fe/GaSe体系中Fe原子与最近邻Ga,Se原子之间存在很强的反铁磁耦合效应,使体系呈现100%自旋极化的半金属性。对于Fe双原子吸附体系,两Fe原子之间的强相互作用导致费米能级附近的单自旋通道随之转变为双自旋通道。其次，通过控制生长条件，在石墨烯片层及具有Moire Patterm的HOPG表面构建Fe、Co量子点及量子线结构，利用扫描隧道显微技术表征铁磁材料表面形貌及电子态结构，认识其电子态耦合特性。接着，结合传统CVD方法，引入热蒸镀CVD生长技术，实现了大面积单层TMDCs晶体的生长，并在此基础上构筑了平面与垂直异质结构，进而实现了超晶格结构的可控生长。最后，基于此前对人工二维Au晶格的相关研究，进一步利用低温MBE生长技术与独特的双探针STM技术对人工二维Au晶格的全新构筑与电学输运性质进行探索。研究发现，人工二维Au晶格中存在宽输运带隙、传播各向异性、电子与空穴输运的不对称性等独特特征。其独特的输运特性可归结为角洞密集排列引起的“电子运动混沌性”与由角洞排列方式决定的“结构对称性”两种因素的共同作用。此外，通过针尖填注技术与结构修饰实现局域超原子以及耦合超原子的构建，最终实现了以超原子共振态作为输运调控“开关”、所修饰Au岛尺寸作为调控“旋钮”的可调共振输运。以上研究结果为二维晶格的生长、超晶格的构筑、二维材料体系量子输运操控以及自旋结构材料的特性研究提供了一定的依据，对下一代二维电子器件的发展也具有重要的参考意义。