Mesoscopic Quantum Critical Regimes and Disorder-Driven Deconfinement

介观量子临界状态和无序驱动的解禁

• 批准号: 0703992
• 负责人: Ganpathy Murthy
• 金额: $ 30万
• 依托单位: University of Kentucky Research Foundation
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-12-15 至 2011-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0703992&HistoricalAwards=false
• 关键词: Mesoscopic; Quantum; Critical; Regimes; Disorder

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.

该奖项支持材料和系统的理论研究和教育，其中无序和相互作用共同创造具有强量子涨落的新状态。在体系统中，强的量子涨落是体量子相变附近的量子临界区的特征，介观系统提供了体量子相变的零维类似物，可以在受控条件下进行研究。该研究建立在PI过去的工作基础上，重点关注基态和低激发态的性质，输运性质中量子临界性的特征，以及介观量子临界状态和体量子临界性之间的交叉。这一研究的成功完成将为强量子涨落介观系统的产生、控制和表征提供基础性的认识。最近，在二维量子反铁磁体的退禁闭相和临界点的识别方面取得了巨大的进展。这种解除限制的制度似乎很难进入现实的晶格自旋系统，可能是不稳定的淬火无序。PI发现，在无序多组分量子霍尔系统中，去禁闭是普遍可能的，并且实际上是由猝灭无序驱动的。 最根本的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了刺猬/单极子。反过来，这些拓扑对象的抑制导致解除限制。需要平滑无序来恢复量子霍尔铁磁体的对称性破缺，并将系统推入去限制态。“nu”= 1的双层系统，实验表明在最低的测量温度耗散，是一个很好的候选人，这样一个deconfined状态。这项研究的主要重点将是调查与带隙费米子和退禁闭自旋相的发生和性质。这项研究的成功完成将使我们对退禁闭相和多组分量子霍尔系统有更深入的了解。对一名博士后和一名研究生进行介观和强关联物理学最新技术的教育是这项研究计划的一个组成部分。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下发生的相变的性质，并被认为能够影响材料的性能。材料在室温或更高温度下的性能。与更熟悉的相变不同，如水到蒸汽的转变，其中热波动负责驱动系统通过转变，量子相变由海森堡的量子力学基本原理驱动，称为不确定性原理。该研究项目的主题是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，以及可能发生的新物质状态，通过研究可能特别容易受到实验和有目的控制的审查的系统。具体的介观系统，例如，涉及量子点和纳米级现象，涉及电子被困在半导体和暴露在大磁场被确定为有前途的调查途径，并持有新的发现的潜力。这项研究的一个重点是了解偏离完美秩序如何影响量子相变以及这种相变所涉及的物质状态的性质。这是一项基础研究，离直接的技术应用还很远，但它奠定了知识基础，有朝一日可能会支持先进技术，利用量子力学原理进行操作，例如量子计算机。在介观和强关联物理学的最新技术方面对博士后和研究生的教育是本提案的一个组成部分。