Charge Fluctuations and Competing Orders in Strongly Correlated Materials

非技术摘要：许多具有潜在重大技术意义的新材料的电子性质是由载流子之间的相互作用决定的。这些关联引发了当前凝聚态物理学中的各种感兴趣的现象，包括出现新的物质状态。这些效应在不同相之间的转变附近最为明显--导体到绝缘体，或者超导体到正常状态--这些转变可以通过外部参数来调节，比如磁场或电场。这些转变的潜在量子性质导致了观察到的行为的复杂性。这项研究解决了在存在其他竞争相的情况下，特别是在量子相变附近，几个电荷有序态的性质和动力学的基本问题。大多数实验涉及测量电荷传输，包括各种与时间相关的方案，使用电场或极高磁场来调节二维晶体和高温超导材料的相变。该项目的一个关键组成部分是对一批不同的年轻研究人员进行教育和培训，为未来在学术界、国家实验室和工业领域的职业生涯做准备。它还包括各种活动，以扩大科学、技术、工程和数学领域中未被充分代表的群体的参与。技术摘要：强关联材料的许多不寻常性质被归因于接近量子临界点，在那里不同类型的有序竞争和共存，甚至可能产生新的相。因此，量子临界点附近的集体涨落的作用越来越被认为是强关联系统物理学中的关键问题之一。尽管人们对各种电荷有序态的涨落特别感兴趣，例如为了阐明它们与铜酸盐高温超导电性的关系，但很少有人研究电荷动力学，而不是自旋动力学。该项目的目的是通过在很长的时间尺度上使用时间分辨电荷传输测量来弥合这一差距，这些测量被证明是对非平衡或玻璃态电荷动力学、量子临界点和新颖的中间相的强大探测器。这项研究旨在为凝聚态物理中的几个基本问题提供答案，这些问题涉及电荷关联和无序的相互作用，它们与高温超导电性的关系，以及各种基态和量子临界点的性质，如二维金属-绝缘体相变和铜酸盐中的磁场调谐超导相变。这一知识对于发展强关联物质的凝聚子场和非平衡现象是必不可少的。

Non-Technical Abstract:Electronic properties of many new materials with potentially great technological importance are dominated by interactions among charge carriers. Those correlations give rise to a variety of phenomena of current interest in condensed matter physics, including the emergence of novel states of matter. These effects are most pronounced near transitions between different phases - conductor to insulator, or superconductor to normal - that can be tuned by an external parameter, like magnetic or electric field. The underlying quantum nature of those transitions contributes to the complexity of the observed behaviors. This research addresses fundamental questions about the nature and the dynamics of several charge-ordered states in the presence of other, competing phases, especially in the vicinity of quantum phase transitions. Most of the experiments involve measurements of charge transport, including various time-dependent protocols, using either electric or extremely high magnetic fields to tune through the phase transitions in two-dimensional crystals and high-temperature superconductor materials. A key component of the project is education and training of a diverse group of young researchers for future careers in academia, national laboratories, and industry. It also incorporates various activities to broaden the participation of underrepresented groups in the areas of science, technology, engineering, and mathematics.Technical Abstract:Many unusual properties of strongly correlated materials have been attributed to the proximity of quantum critical points, where different types of orders compete and coexist, and may even give rise to novel phases. The role of collective fluctuations near quantum critical points is thus increasingly recognized as one of the key questions in the physics of strongly correlated systems. Even though fluctuations of various charge-ordered states have been of particular interest, e.g. to clarify their relationship with high-temperature superconductivity in cuprates, there have been few studies of charge, as opposed to spin, dynamics. The aim of the project is to bridge this gap by using time-resolved charge transport measurements on very long time scales, proven to be powerful probes of out-of-equilibrium or glassy charge dynamics, quantum critical points, and novel, intermediate phases. The research is designed to provide answers to several fundamental questions in condensed matter physics concerning the interplay of charge correlations and disorder, their relationship to high-temperature superconductivity, and the nature of various ground states and quantum critical points, such as the two-dimensional metal-insulator transition and the magnetic-field-tuned superconducting transition in cuprates. This knowledge is essential to the development of condensed matter subfields of strongly correlated materials and out-of-equilibrium phenomena.