Charge Fluctuations and Competing Orders in Strongly Correlated Materials

摘要：许多具有潜在重大技术意义的新材料的电子特性是由载流子之间的相互作用决定的。这些相关性引起了当前凝聚态物理学中各种各样的现象，包括物质新状态的出现。这些效应在不同相位之间的转换附近最为明显——导体到绝缘体，或超导体到正常——这些可以通过外部参数（如磁场或电场）来调节。这些跃迁的潜在量子性质有助于观察到的行为的复杂性。本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，关于若干电荷有序态的性质和动力学的基本问题。大多数实验涉及电荷传输的测量，包括各种时间相关协议，使用电场或极高的磁场来调谐二维晶体和高温超导体材料的相变。该项目的一个关键组成部分是教育和培训不同群体的年轻研究人员，为未来在学术界、国家实验室和工业界的职业生涯做好准备。它还包括各种活动，以扩大代表性不足的群体在科学、技术、工程和数学领域的参与。技术摘要：强相关材料的许多不寻常性质归因于量子临界点的邻近，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相关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波动特别感兴趣，例如澄清它们与铜酸盐中的高温超导性的关系，但与自旋相反，对电荷动力学的研究很少。该项目的目的是通过在很长时间尺度上使用时间分辨电荷输运测量来弥补这一差距，该测量已被证明是非平衡或玻璃电荷动力学、量子临界点和新型中间相的强大探针。该研究旨在回答凝聚态物理学中有关电荷相关和无序的相互作用、它们与高温超导的关系以及各种基态和量子临界点的性质的几个基本问题，例如铜酸盐中的二维金属-绝缘体转变和磁场调谐超导转变。这些知识对于发展强相关材料的凝聚态子场和不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.