LaAlO3/SrTiO3异质界面奇异物理性质的理论研究

The prime goal of this research plan here is to investigate and control novel electronic and magnetic phases, arising from electronic and orbital reconstruction at hetero-interfaces in complex oxides. Such reconstructions provide a means to create,and ultimately to control and exploit,novel electronic and magnetic phases that intrinsically cannot exist in the bulk. Moreover,being bound to the interface, these states will be characterized by a reduced dimensionality, providing a rich basis for exciting new physics. A good system to start our research is LaAlO3/SrTiO3 heterostructure,in which two-dimensional electron gas(2DEG) has been found to emerge between two otherwise insulating materials.The concrete research plans are (i) to use first principles electronic structure calculations and thermodynamics methods to study LaAlO3/SrTiO3 heterostructures with different growth orientations,e.g.,(110) and (001) directions, understand the atomic structures and stability of complex interfaces,investigate the metal-insulator transition arising as a result of a combination of polar catastrophe,oxygen vacancy, atomic intermixing,epitaxial strain and the external electric field, and establish a theoretical basis for the identification of the most promising combination of materials and the understanding of their interface characteristics.(ii) to understand structural, electronic and orbital reconstructions at the interfaces on these strongly correlated complex oxides by developing realistic many-body model Hamiltonians.(iii) to theoretically analyze the transport behavior on the interface of heterostructures fabricated with different transition metal oxides, and develop a universal heteroepitaxial materials system.

本项目从复杂氧化物异质界面的原子结构，电子结构的层面出发，研究复杂氧化物异质界面的电输运性质，探索界面导电机制，揭示外电场的调控规律，为实现复杂氧化物在下一代量子器件中的潜在应用提供理论基础和技术路径。采用基于密度泛函的第一性原理计算和界面稳定性研究的热力学方法，来研究不同生长取向下的LaAlO3/SrTiO3异质界面结构、电子能带结构和金属-绝缘体相变。研究极化激变、氧空穴、界面原子混合、外延应力以及外电场等因素对异质界面的电输运性质的影响；构建微观模型，研究低维强关联界面的电子、轨道重构，模拟基态及激发态性质 ,探讨各种长程有序相的稳定性；最后，借鉴LaAlO3/SrTiO3异质界面的研究经验,通过筛选不同的过渡金属氧化物组装成异质结来提高界面导电性能，优化结构设计,探索复杂氧化物在纳米器件中的技术应用。

本项目研究了不同生长取向下的LaAlO3/SrTiO3异质界面结构、电子能带结构和金属-绝缘体相变。研究极化激变、氧空穴、界面原子混合、外延应力以及外电场等因素对异质界面的电输运性质的影响。在第一性原理计算和热力学模型基础上，提出了zigzag 型复杂界面结构，利用极化激变模型完美的解释了LaAlO3/SrTiO3(110)的界面导电机制，并提出了对应的临界厚度概念。借鉴LaAlO3/SrTiO3异质界面的研究经验，采用第一性原理计算和双交换模型探索分析了(LaMnO3)n/(SrMnO3)2n超晶格在应力作用下可调的丰富的磁有序和轨道有序。