Physics of Proximate Metallic and Insulating Phases

*非技术摘要*本项目将继续进行实验，以制造和表征金属和绝缘体非常接近的材料。在给定的材料中，金属相和绝缘相的接近有两种方式：这两种相同时共存并相互竞争，或者一种主导相可以转变为另一种。在这两种情况下，外部参数如温度或磁场的变化都会引起金属-绝缘体的转变，并伴随着电学性质的显着变化。选择用于研究的材料包括可通过金属-绝缘体转变进行调谐的超薄无序铁磁性薄膜、由竞争铁磁金属和绝缘相组成的复合氧化物、平行/垂直于碳平面表现出高度金属/绝缘行为的掺杂石墨，以及凭借其不同寻常的电子结构具有导电边缘和表面态与绝缘内部共存的“拓扑绝缘体”。理解这些研究的结果有望揭示重要的新物理学，这些物理学将推动新型复合金属绝缘体材料的设计，这可能对造福社会的新技术具有重要意义。这项建议支持的研究和教育/推广活动将使研究生和本科生在学术、工业或政府环境中从事令人满意和富有成效的职业生涯。*技术摘要*本项目将进行实验，以制造和表征金属和绝缘相紧密接近的材料，从而产生复杂和新颖的现象学。所选择的研究材料集中在四类材料上：(1)超薄铁磁薄膜，通过改变无序强度可以通过金属-绝缘体转变进行调谐；(2)混合相锰氧化物，在绝缘体-金属渗流转变附近共存的金属和绝缘相之间存在依赖温度、应变和场的竞争；(3)石墨，其中嵌入诱导的面内“超金属”电导率同时出现平面外绝缘电导率；以及(4)拓扑绝缘体，由于其不寻常的电子能带结构，具有导电边缘和表面态，与绝缘内部共存。理解这些研究的结果有望揭示重要的新物理学，这些物理学将在近金属相和绝缘相的统一主题下，驱动纳米尺度的新型复合金属绝缘体材料的设计。这项研究的相关研究和教育/推广活动将使研究生和本科生在学术、工业或政府环境中找到令人满意和富有成效的职业生涯。

**** NON-TECHNICAL ABSTRACT ****This project will pursue experiments to fabricate and characterize materials in which metals and insulators are in close proximity. The proximity of metallic and insulating phases in a given material arises in two ways: both phases simultaneously coexist and compete with each other, or one dominant phase can be transformed to the other. In both cases the change of an external parameter such as temperature or magnetic field can induce metal-insulator transitions accompanied by pronounced changes in electrical properties. The materials chosen for study include ultra thin disordered ferromagnetic films which can be tuned through a metal-insulator transition, complex oxides which comprise competing ferromagnetic metal and insulating phases, doped graphite which exhibits highly metallic/insulating behavior parallel/perpendicular to the carbon planes, and "topological insulators", which by virtue of their unusual electronic structure have conducting edge and surface states coexisting with insulating interiors. Understanding the results of these studies promises to unveil important new physics that will drive the design of novel composite metal-insulator materials that may be important for new technologies for the benefit of society. The research and education/outreach activities supported by this proposal will lead to the placement of graduate and undergraduate students in satisfying and productive professional careers within academic, industrial or government settings.**** TECHNICAL ABSTRACT ****This project will pursue experiments to fabricate and characterize materials in which metallic and insulating phases are in close proximity, thereby giving rise to complex and novel phenomenology. The materials chosen for study focus on four classes: (1) ultra thin ferromagnetic films that can be tuned through a metal-insulator transition by varying the disorder strength; (2) mixed phase manganites in which there is a temperature, strain and field-dependent competition between coexisting metallic and insulating phases near an insulator-metal percolation transition; (3) graphite in which there is an intercalation-induced in-plane "supermetallic" conductivity simultaneously appearing with an out-of-plane insulating conductivity; and (4) topological insulators, which by virtue of their unusual electronic band structure have conducting edge and surface states coexisting with insulating interiors. Understanding the results of these studies promises to unveil important new physics that will drive the design of novel composite metal-insulator materials at nanoscale dimensions under the unifying theme of proximate metallic and insulating phases. The associated research and education/outreach activities of this research will lead to the placement of graduate and undergraduate students in satisfying and productive professional careers within academic, industrial or government settings.