Meta-to-Insulator Transition at Correlated Electron Interfaces: In-Situ Growth and Characterization of Thin Oxide Films

****非技术摘要****该奖项支持实验凝聚态物理研究，研究薄膜和多层复杂氧化物化合物界面附近的不寻常物理性质。这些人工结构的材料，表现出奇特的功能，与未来先进的电子设备和能源应用有关。特别是这些材料的界面普遍表现出不同于相应体化合物的新性能。另一方面，几乎所有的电子设备都是从对界面势垒形成、电子/磁性结构和控制的理解开始的：界面就是设备。将复杂氧化物的多种物理性质结合到器件中需要从一个基本的理解开始。令人兴奋的是，现代氧化物薄膜生长和探针技术提供了必要的原子尺度精度来构建界面结构，并显示其电子特性，如金属到绝缘体的转变，这正是本项目所研究的。这项研究的目标是了解并最终学习如何操纵氧化物材料界面上的输运性质，从而为下一代电子设备设计新的功能。此外，这一努力的一个重要成果将是将材料制造、表征、分析和设计整合到一个独特的研究和教育计划中，以基本了解复杂的氧化物界面和培训未来的科学和技术（S&amp；T）劳动力。研究生和本科生都将参与材料制造和表征工作，他们将培养“化学”和“物理”思考的基本能力。****技术摘要****本研究项目旨在研究如何利用表面或界面上的对称性破坏和空间限制来操纵过渡金属氧化物（TMO）材料薄膜中的紧急性质，特别是金属-绝缘体过渡（MIT）。该目标将通过利用一套全面的原位材料生长和自动分辨表征能力来实现。越来越清楚的是，TMOs的表面、界面和薄膜显示出丰富多样的迷人特性，这些特性与体现象相关，但不完全相同。麻省理工学院就是其中之一。虽然这些现象的机制仍然存在激烈的争论。对这些现象的可能解释包括掺杂电子和氧空位、相互扩散和晶格畸变。本项目将利用原子表征结合原位生长能力，探索应变、缺陷和氧空位、化学成分和界面结构畸变在界面和薄膜上出现MIT的作用。具体来说，它将专注于（Sr,Ca）RuO3和（Sr,Ca）VO3这两种众所周知的伪立方金属钙钛矿的薄膜，但处于MIT的边缘。通过改变基底、薄膜厚度、阳离子位点组成引起的应变，该项目旨在深入了解驱动MIT的扬-泰勒扭曲和电子-电子相关的相互作用。

****NONTECHNICAL ABSTRACT****This award supports experimental condensed-matter physics research on the unusual physical properties near the interface of films and multilayers of complex oxide compounds. These artificially structured materials, which exhibit exotic functionalities, are relevant to future advanced electronic devices and energy applications. Especially, the interfaces of these materials generally show new properties different from the corresponding bulk compounds. On the other hand, almost all electronic devices began with an understanding of interface barrier formation, electronic/magnetic structure, and control: the interface is the device. Incorporating the diversity of physical properties of complex oxides into devices needs to begin with a basic understanding. What is very exciting is that modern oxide thin-film growth and probe techniques give the requisite atomic-scale precision to construct interface structure and manifest its electronic properties such as metal to insulator transition, which is exactly the research in this project. The goal of this research is to understand and ultimately learn how to manipulate the transport properties at the interfaces of oxide materials and thus to design new functionalities for next generation of electronic devices. Moreover, a significant product of this endeavor will be to integrate materials fabrication, characterization, analysis and design into a unique research and educational program for the basic understanding of complex oxide interfaces and the training of the future science and technology (S&T) workforce. Both graduate and undergraduate students will be involved in both material fabrication and characterization efforts and they will develop the essential ability to think "chemically" and "physically". ****TECHNICAL ABSTRACT****This research project is designed to study how the broken symmetry at a surface or interface and spatial confinements can be used to manipulate the emergent properties in a thin film of transition metal oxide (TMO) materials, especially the metal-insulator transition (MIT). The objective will be achieved by utilizing a comprehensive set of in-situ materials growth and atomically-resolved characterization capabilities. It is becoming increasingly clear that surfaces, interfaces, and thin films of TMOs display a rich diversity of fascinating properties that are related to, but not identical to, the bulk phenomena. MIT is one of these emerging properties. While the mechanisms for these phenomena are still hotly contested. Possible explanations for these phenomena include doping with electrons and oxygen vacancies, interdiffusion and lattice distortion. This project is going to take advantage of atomic characterization combined with in-situ growth capability to explore the role of strain, defects and oxygen vacancies, chemical composition and interface structural distortion in MIT emerging at interfaces and thin films. Specifically, it will focus on thin films of (Sr,Ca)RuO3 and (Sr,Ca)VO3, two well-known pseudo-cubic metallic perovskites, but at the verge of MIT. By varying strain induced by substrate, film thickness, cation-site composition, the project aims to gain insight into the interplay of Jahn-Teller distortion and electron-electron correlation driving the MIT.