磁性掺杂拓扑绝缘体的第一性原理研究

Topological insulator, as a new quantum state of matter, is attracted by its insulating and conductive double characteristics. Combined with ferromagnetic order, topological insulator will trigger more novel quantum phenomena, and thus has broad potential application in the field of quantum computers and spintronics. In this proposal, we will employ first-principles calculations combining Monte Carlo simulation to study magnetically doped topological insulator, including three research parts as follows: First, from the perspective of material growth, we will focus on the formation and stability of the magnetic topological insulator materials in the presence of microstructures containing magnetic impurity and defect states. We aim to assess and predict the likelihood of establishing ferromagnetic order in topological insulator via magnetic atoms doping, and provide theoretical reference and guidance for the experimental preparation. Second, based on the comparison of microcosmic magnetic interactions with macroscopic magnetic properties, we will try to charify the effect of microstructures on the topological, electronic and magnetic properties in magnetic topological insulator, and finally find out a law to achieve ferromagnetic topological insulators. Third, we will introduce external field (electronic field, magnetic field and stress) to modulate the topological character, electronic structure and magnetic properties as well as their relationship, from which we devote to explore the magnetic coupling mechanism of ferromagnetic topological insulator. Through these studies, we will offer an guidance for the experimental preparation of ferromagnetic topological insulators and provide a preparation for the discovery of novel quantum phenomena, so as to lay a foundation for the industrial applications of magnetic topological insulator.

作为一类全新的量子物质，拓扑绝缘体具有迷人的绝缘和导电双重特性，结合铁磁序又能够导致更多新奇的量子效应，在量子计算机和自旋电子学等领域具有广阔的应用前景。本项目将利用第一性原理计算结合蒙特卡罗模拟方法研究磁性掺杂拓扑绝缘体材料，集中开展以下几个工作：1.从材料生长的角度研究磁性拓扑绝缘体材料中磁性杂质及缺陷态等微结构的存在及形成条件，从原理上评估和预测磁性掺杂拓扑绝缘体形成铁磁序的可能性，为实验制备提供理论参考和指导。2.在微观磁相互作用与宏观磁特性比较的基础上，阐明微结构对磁性拓扑绝缘体的拓扑特性、电学性质、磁性的影响，揭示拓扑绝缘体中实现铁磁序的规律。3.结合外场（电场、磁场、应力）调控分析磁性拓扑绝缘体中拓扑性、电子结构和铁磁性之间的关联，进一步探索铁磁拓扑绝缘的磁性耦合机理。通过项目研究指导铁磁绝缘体的实验获取，为新奇量子现象的发现提供准备，并为磁性拓扑绝缘体的工业应用奠定基础。

拓扑绝缘体与磁性的结合会产生一些重要且有趣的物理现象。研究人员发现在磁性掺杂的拓扑绝缘体中会出现磁电效应、量子化的反常霍尔效应等新奇量子现象，因而在量子计算机和自旋电子学等领域具有广阔的应用前景。.本项目主要通过第一性原理计算结合蒙特卡罗模拟方法研究磁性掺杂拓扑绝缘体材料。取得的主要成果包括：（1）找到了纯Bi2Se3拓扑绝缘体薄膜外电场作用下系统能带演化的规律。发现体系带隙大小由电荷转移和自旋轨道耦合的竞争决定。（2）通过外加电场作用可以有效调控Cr掺杂Bi2Se3薄膜的能带结构，这对于拓扑绝缘体材料的拓扑相变研究及实验改性提供了有力的参考。（3）获得了外加应力作用下拓扑绝缘体Bi2Se3能带的演化规律。（4）找到了Bi2(Te1-xSex)3薄膜能带调控机制，获得了合适的合金成分比例，为实验制备真正拓扑绝缘体提供指导，该结果为拓扑绝缘体合金材料设计及实验制备提供了重要的理论参考。（5）发现Cr掺杂Bi2Se3体系中磁性原子间最近邻的交换耦合及温度对系统磁性具有重要影响，并给出了对应的变化关系。.系列研究成果表明外加电场、外加应力及替代掺杂能够有效的调控拓扑绝缘体的物性，相关结果为人们加深对磁性拓扑绝缘体相变、耦合机制等研究提供了重要的帮助，也为实验调控提供了重要依据，并为磁性拓扑绝缘体的工业应用奠定基础。.我们还研究了（1）自旋零带隙半导体PbPdO2薄膜的生长机理和外加电场调控并在实验上成功制备了不同择优取向的薄膜样品。（2）利用第一性原理研究方法系统研究了缺陷、替代、掺杂等对Ni/HfO2界面有效功函数的影响，并提出了多种有效的外场调控方案。