钙钛矿氧化物异质结中界面电子结构调制的研究

Transition metal oxides with the perovskite structure are typical correlated electron materials. In these systems, the couplings between multi-degree of freedom like charge, spin, orbital, and lattice, give rise to fasinating physical properties and promise board potential applications. To utilize correlated electron materials in devices, thin films and heterostructures of oxides are the key start points. In perovskite heterostructures, complex reconstructions of both the crystal structure and electronic structure will occur around the interfaces between two oxides. The reconstruction of crystal structure denotes the reshape of perovskite lattices driven by the strain/stress from the lattice mismatch, which will change materials' properties. Due to the electron transfer across the interfaces (like in the semiconductor PN junctions), the electron structure near interfaces, not only the charge distribution, but also the magnetic structures/couplings and orbital orders, will be rebuilt. In this project, several kinds of perovskite heterostructures will be investigated. The main goal is to reveal the underlying physical mechanisms during the interfacial reconstructions due to the lattice mismatch and electron transfer, and how to control them. The main subjects include: 1) Magnetic transitions and couplings in magnetic oxides superlattices (e.g. LaMnO3/SrMnO3, BiFeO3/LaSrMnO3 etc.), and the electrical controllable exchange bias; 2) The ferroelectric field effects and tunnel junctions based on ferroelectric/manganite heterostructures. These topics will be studied mainly from the theoretical aspect, while some related experiments will also be carried out.

钙钛矿结构过渡金属氧化物是典型的关联电子材料，其中自旋、轨道、电荷、晶格多重自由度相互耦合，展现出丰富的物理特性和广阔的应用前景。而氧化物薄膜和异质结则是关联电子材料走向实际器件应用的关键起点。在钙钛矿异质结中，两种材料界面处将发生复杂的晶格重组与电子重组。其中晶格重组指通过应力作用改变钙钛矿结构晶格畸变，从而改变材料的物性；而电子重组则是指通过界面处的电子转移（类似于半导体PN结）来调节界面处的电子结构（包括电荷分布、磁结构和耦合、轨道序）。本项目将研究多种钙钛矿结构异质结，重点关注晶格失配、电子转移等因素导致的界面重组效应以及如何人工控制异质结界面物理性质。主要研究内容包括:1)磁性氧化物超晶格(包括LaMnO3/SrMnO3,BiFeO3/LaSrMnO3等)的磁性转变和耦合、可电场控制的交换偏置；2）铁电/锰氧化物异质结的铁电场效应、铁电隧道结。本项目研究将以理论为主、实验为辅。

按照本项目既定计划，在过去四年中，我们系统开展了钙钛矿氧化物异质结及相关体系物理性质的理论研究，并且做了一些理论实验相结合的探索。.首先，我们研究了钙钛矿氧化物薄膜和异质结中的诸多物理效应，例如磁性转变，电荷转移，杂化铁电、量子限制效应，晶格重组等。.其次，我们设计了基于钙钛矿氧化物异质结的电控磁器件原型，包括锰氧化物双层以及铁酸铋双层异质结。.再次，我们还研究了钙钛矿锰氧化物块体和异质结中的拓扑相以及边缘态。.最后，我们还拓展研究了几类二维材料的超导性能、半导体材料TiO2表面的光催化、铁基超导家族中的多铁性等。.本项目的研究成果对深入理解钙钛矿氧化物异质结界面物理，推动基于钙钛矿氧化物材料的器件设计具有一定的价值和意义。.本项目资助发表论文40篇，其中SCI收录39篇，中文核心1篇，另有英文专著1章。培养博士、硕士研究生数十人，培养博士后两人。.基于我们本项目的研究成果以及前期积累，受邀为著名凝聚态物理综述期刊Advances in Physics撰写长篇综述1篇。