基于二维过渡金属硫属化合物的纳米结构中的磁性研究

Two dimensional (2D) transition metal dichalcogenides (TMDs) have a wide variety of chemical composition, structures and symmetries, and 2D TMDs can be semiconductors, semi-metals or metals. Then introduction of foreign atoms can make nanostructures based on 2D TMDs show rich magnetic properties. We will perform systematic investigations of: (1) the stability and magnetic properties of a single substitutional atom in or adatom on a single layer TMD as well as the coupling between two magnetic impurity atoms, through which we can predict thermodynamic stable systems with ferromagnetic order and reveal the variation of mechanism for magnetic moments of impurity atoms and the exchange interaction between them with respect to the chemical composition and electronic properties of single layer TMDs; (2) the magnetic properties of single layer TMDs adsorbed with ordered metal atoms and double layer TMDs intercalated with metal atoms in order to predict stable and magnetic hybrid nanostructures of 2D TMDs and metal-atom layers; (3) effects of magnetism and spin-orbit coupling on the electronic structure of 2D TMDs as well as the tuning of electronic and magnetic properties of the systems with external fields to explore possible applications of the predicted magnetic systems in spintronics or valleytronics devices. In these studies we will also develop theoretical methods to obtain ordered nanostructures based on 2D TMD through adsorption or intercalation of metal atoms and to include different types of external fields simultaneously for tuning the electronic and magnetic properties of the studied systems.

二维过渡金属硫属化合物（TMD）具有多样的化学组成、结构形式和对称性，呈现半导体、半金属或金属性，基于二维TMD引入外来原子得到的纳米结构可具有丰富的磁性质。我们将系统研究：（1）单层TMD中单个替代或吸附原子的稳定性与磁性质以及两磁性杂质之间的耦合形式与强度，预言热力学稳定并呈现铁磁耦合的系统，揭示杂质磁矩的产生机制及其交换相互作用随着单层TMD的化学组成和电子性质的变化规律；（2）金属原子在TMD单层上的有序吸附结构或双层中有序插层结构的磁性质，预言稳定且有磁的复合有序系统；（3）磁性与自旋轨道耦合效应对二维TMD自身电子性质的影响以及外场对系统电子和磁性质的调制，预测有磁体系应用于自旋或谷电子学器件的可能性。在研究中也将发展预言基于二维TMD的有序吸附或插层构型以及处理在多种外部因素同时作用下体系磁性质的变化的理论方法。

二维过渡金属硫属化合物(TMD)具有丰富的化学组成和结构形式，其本身和在外部调控下可展现多样的磁性质、电子和自旋特性。在本项目中，我们使用第一性原理计算方法与所发展的基于瓦尼尔函数计算自旋和反常霍尔电导率的算法程序，研究了单层1T’相MX2(M=Mo,W; X=S,Se,Te)含嵌入3d过渡金属原子时的磁性质、其本身的自旋霍尔效应以及具有铁磁序的单层和多层Fe3GeTe2的反常霍尔效应。通过对3d过渡金属替代掺杂的1T’-MX2的磁性质的系统研究，我们预言嵌入Mn的1T’-MX2最有希望实现铁磁序，其他替代原子则向1T’-MX2掺杂电子或空穴。1T’-MX2独特的结构形式和强的自旋轨道耦合使其具有拓扑非平庸的能带结构，而我们发现其本征自旋霍尔电导率(SHC) 均是非量子化的，这源于带隙附近状态的自旋是非守恒的；我们同时预言其半导体性系统具有强的SHC开关效应，垂直电场可使其SHC在拓扑相变点跃变到零，而半金属性的 1T’-MTe2的SHC随着电场强度连续的下降。单层和多层Fe3GeTe2均具有铁磁序，我们的计算表明双层系统平均每层的反常霍尔电导率远高于单层系统，也高于体结构的值，这源于双层系统在第一布里渊区边界附近存在众多的避免交叉费米线。我们还研究了1T’-MX2在应变下的拓扑相变以及其合金体系的拓扑性质。以上结果为在基于二维TMD的纳米结构中实现铁磁序与新奇的自旋特性提供了物理机制和预言。