Transport and Carrier Dynamics Near the Metal-Insulator Transition in VO2

非技术描述：二氧化钒是一种材料，在室温(约68摄氏度)以上经历从电绝缘体到电导体的转变。这种行为允许它充当电气开关，这是计算机中晶体管所需的基本功能。然而，对这种转变的完整微观理解仍然缺乏，阻碍了这种材料的未来应用。该项目结合了该团队的理论和实验专业知识，以深入了解过渡的微观机制，并发现控制过渡的新方法。实验表征为理论模型的进一步发展提供了反馈，这些模型也做出了进一步的理论预测，以指导实验工作。各种外展和教育活动包括：(1)为学生提供高度专题研究领域的理论和实验实践研究经验；(2)参加国际实习计划，在学年引入本科生；(3)通过长期的行业合作向行业传播研究成果；以及(4)特别通过与历史上有代表性的黑人学院和大学的现有合作，扩大代表不足的群体的参与。技术说明：二氧化钒从低温绝缘相转变为高温金属相，在此过程中，电阻率可变化高达10万倍，同时伴随着红外反射率的大幅变化。体相二氧化钒(VO2)在341K的温度驱动金属绝缘体转变的基本机制在其发现50多年后仍在争论中。具体地说，有必要了解导致异常输运性质的微观物理，特别是绝缘态中金属团簇的存在。混合相不能用简单的相分离模型来解释，也不能用简单的半导体或渗流模型来解释输运。这个项目结合了实验和理论工作，每一项都为另一项提供了关键的反馈。该方法在微观层面上解决了涉及的相关物理过程，即与离子位移相关的电子运动。对混合相的详细实验输运研究是该项目的关键部分，特别是电噪声和隧道光谱。该团队还在研究新型晶体管类结构和压电致应变效应，目标是实现电子控制的转变。通过将VO2视为一个强相互作用的电子-离子系统，该理论模型包含了VO2的基本物理。非微扰多体技术被用来研究如何发生转变和金属团簇的出现，超出了密度泛函理论的范围，

Non-technical Description: Vanadium dioxide is a material that undergoes a transition from an electrical insulator to an electrical conductor just above room temperature (about 68 degree C). This behavior allows it to act as an electrical switch, which is an essential functionality required for transistors in computers. However, a complete microscopic understanding of this transition is still lacking, hindering future applications of this material. This project combines theoretical and experimental expertise of the team to develop an in-depth understanding of the microscopic mechanisms for the transition and discover new approaches to control it. Experimental characterization acts as a feedback for the further development of theoretical models, and these models also make further theory predictions to guide experimental efforts. Various outreach and education activities include: (1) providing the theoretical and experimental hands-on research experience in highly topical research areas for students; (2) participating in an international internship program to bring in undergraduates during the academic year; (3) disseminating research findings to industry through long-standing industrial collaborations; and (4) broadening the participation of under-represented groups specifically through an existing collaboration with Historically Black Colleges and Universities. Technical Description: Vanadium dioxide transforms from a low-temperature insulating phase to a high-temperature metallic phase, during which the electrical resistivity can change by a factor of as much as 100,000, accompanied by a large change in infrared reflectivity. The fundamental mechanism of the temperature-driven metal-insulator transition of bulk vanadium dioxide (VO2) at 341 K is still under debate, over fifty years after its discovery. Specifically, there is a need to understand the microscopic physics responsible for the anomalous transport properties, in particular the presence of metallic clusters in the insulating state. The mixed phase cannot be explained in terms of a simple phase separation model; nor can a simple semiconductor or percolation model explain the transport. This project combines experimental and theoretical efforts, with each providing a crucial feedback for the other. The approach addresses the relevant physical processes involved, namely electron motion correlated with ionic displacements, at a microscopic level. Detailed experimental transport studies of the mixed phase are a key part of the project, particularly electrical noise and tunneling spectroscopy. The team is also investigating novel transistor-like structures and piezoelectric-induced strain effects with a goal of an electrically controlled transition. The theoretical model contains the essential physics of VO2, by treating it as a strongly interacting electron-ion system. Non-perturbative many-body techniques are applied to study how the transition can occur and metallic clusters appear, beyond the reach of density functional theory,