Mesoscopic Quantum Critical Regimes and Disorder-Driven Deconfinement

技术摘要：该奖项支持材料和系统的理论研究和教育，在这些材料和系统中，无序和相互作用共同创造出具有强烈量子涨落的新状态。在大块系统中，强量子涨落是大块量子相变附近的量子临界区的特征。介观系统提供了大块量子相变的零维模拟，可以在可控条件下进行研究。这项研究建立在PI过去工作的基础上，主要集中在基态和低激发态的性质，输运性质中量子临界性的特征，以及介观量子临界区和体量子临界性之间的交叉。这项研究的成功完成将为建立、控制和表征具有强量子涨落的介观系统提供基础认识。最近，在识别二维量子反铁磁体中的解禁制相和临界点方面取得了巨大的进展。在现实的晶格自旋系统中，这样的解禁制态似乎很难获得，而且可能是不稳定的，甚至可能是猝灭的无序。PI发现，在无序多组分量子霍尔系统中，退禁闭通常是可能的，并且实际上是由猝灭的无序驱动的。根本原因是最低朗道能级的自旋-电荷关系，它通过局域电荷守恒禁止刺激性/单极子。反过来，对这些拓扑对象的抑制导致去受限。需要光滑无序来恢复量子霍尔铁磁体的破缺对称性，并将系统推入解禁闭状态。“nu”=1双层系统在实验上显示了在最低测量温度下的耗散，是这种去禁闭状态的一个很好的候选者。这项研究的主要重点将是研究有缝隙的费米子和解禁闭自旋的相的出现和性质。这项研究的成功完成将导致对解禁闭相和多组分量子霍尔系统的更深入的理解。对博士后和研究生的介观和强关联物理最新技术的教育是这项提议的组成部分。非技术概述：该奖项支持材料和系统的理论研究和教育，这些材料和系统将研究在绝对零度发生的相变的性质，据信能够在室温以下甚至更高的温度下影响材料的性质。与更常见的相变，如水到水蒸气的转变，其中热涨落负责推动系统通过转变，量子相变是由量子力学的基本原理驱动的，因为海森伯格被称为测不准原理。这项研究项目的一个主题是通过对可能特别容易受到实验和有目的控制的系统的研究，更好地了解这些不寻常的相变及其对材料和材料系统的性质，特别是电子性质的影响，以及可能出现的新的物质状态。例如，涉及量子点的特定介观系统和涉及捕获在半导体中并暴露在大磁场中的电子的纳米级现象被确定为有希望的探索途径，并具有新发现的潜力。这项研究的主旨是了解偏离完美秩序如何影响量子相变以及转变所涉及的物质状态的性质。这是一项基础性研究，距离直接的技术应用还很远，但它奠定了智力基础，有朝一日可能会用利用量子力学原理进行操作的设备来支持先进技术，例如量子计算机。对博士后和研究生进行介观和强关联物理最新技术的教育是这项提议的组成部分。

TECHNICAL SUMMARY:This award supports theoretical research and education on materials and systems in which disorder and interactions conspire to create novel states with strong quantum fluctuations. In bulk systems strong quantum fluctuations are characteristic of the quantum critical regime near the bulk quantum phase transition.Mesoscopic systems offer zero-dimensional analogs of bulk quantum phase transitions which can be studied under controlled conditions. The research builds on the PI's past work and is focused on the nature of the ground and low-lying excited states, the signatures of quantum criticality in transport properties, and on the crossover between mesoscopic quantum critical regimes and bulk quantum criticality. The successful completion of this research will provide the fundamental understanding to enable the creation, control, and characterization of mesoscopic systems with strong quantum fluctuations.Recently, tremendous progress has been made in identifying deconfined phases and critical points in two-dimensional quantum antiferromagnets. Such deconfined regimes appear difficult to access in realistic lattice spin systems, and are probably unstable to quenched disorder. The PI finds that deconfinement is generically possible in disordered multicomponent quantum Hall systems, and is in fact driven by quenched disorder. The fundamental reason is the spin-charge relation of the lowest Landau level, which forbids hedgehogs/monopoles by local charge conservation. In turn, the suppression of these topological objects leads to deconfinement. Smooth disorder is needed to restore the broken symmetry of the quantum Hall ferromagnet and push the system into a deconfined state. The "nu" = 1 bilayer system, which experimentally shows dissipation at the lowest measured temperatures, is a good candidate for such a deconfined state. The primary focus of this research thrust will be to investigate the occurrence and properties of phases with gapped fermions and deconfined spinons. The successful completion of this research will result in a deeper understanding of both deconfined phases and multicomponent quantum Hall systems.The education of a postdoc and a graduate student in the latest techniques of mesoscopic and strongly correlated physics is an integral part of this proposal.NON-TECHNICAL SUMMARY:This award supports theoretical research and education on materials and systems that will study the nature of phase transitions which occur at the absolute zero of temperature and are believed to be able to affect the properties of materials at temperatures up to room temperature and possibly beyond. Unlike more familiar phase transitions, like the transformation of water to steam, in which thermal fluctuations are responsible for driving the system through the transformation, quantum phase transitions are driven by a fundamental principle of quantum mechanics due to Heisenberg known as the uncertainty principle. A theme of this research project is to better understand these unusual phase transitions and the affect that they have on the properties, particularly electronic properties, of materials and material systems, and the new states of matter that may occur, through the study of systems that may be particularly susceptible to the scrutiny of experiment and purposeful control. Specific mesoscopic systems involving, for example, quantum dots and nanoscale phenomena involving electrons trapped in semiconductors and exposed to large magnetic fields are identified as promising avenues of inquiry and hold potential for new discoveries. A thrust of the research is to understand how deviations from perfect order affect quantum phase transitions and the nature of the states of matter involved in the transformation.This is fundamental research that is distant from immediate technological application, but it lays the intellectual foundations that may someday support advanced technologies with devices that exploit quantum mechanical principles for their operation, for example quantum computers.The education of a postdoc and a graduate student in the latest techniques of mesoscopic and strongly correlated physics is an integral part of this proposal.