Disordered Critical Quantum Magnetic Systems

该奖项支持量子磁学领域的基础理论研究和教育，以及量子磁体中无序的作用。铜酸盐和重费米子材料具有磁性和非磁性相之间的相变。通常，这些相变是由化学取代驱动的，化学取代也会将无序引入系统。根据其性质和强度，无序可以导致磁系统临界行为的实质性变化。PI旨在研究无序和电子耗散对量子磁系统临界行为和集体激发的影响。与弱无序的经典问题相反，量子临界系统中的无序相关性没有既定的标准。PI将在量子系统中搜索相关标准。虽然有大量的系统，其中临界行为被无序修改，PI将集中在两个实验相关系统的研究：金属f-电子合金UCu 5-xPdx，其中所谓的“非费米液体”（NFL）行为已被观察到，和低维稀绝缘磁体La 2Cu 1-z（Zn，Mg）zO 4。这些系统具有共同的特征：（i）它们可以通过化学取代通过量子临界点（QCP）从磁有序相调谐到顺磁相;（ii）它们具有接近QCP的异常磁性行为;（iii）它们是无序合金。PI将使用现代场论方法研究这些系统，并将结果与最近的实验数据进行比较。这些比较将作为理论发展的过滤器。这项工作的成功，涉及无序量子磁体的标准和普遍行为的分类和阐明，将对量子磁学领域产生广泛而直接的影响。 这项工作对本科生和研究生教育产生了更广泛的影响。这项工作还支持努力激发属于代表性不足群体的高年级学生对凝聚态物理的兴趣，并推广到小学生，以激发下一代科学家的兴趣。该奖项支持量子磁学领域的基础理论研究和教育，以及量子磁体中无序的作用。PI将专注于化学取代和无序的影响，这通常会导致量子磁体的性质。化学取代使得能够通过量子相变进行调谐。量子相变不同于经典相变，并且具有很大的基本兴趣。它们可能为理解重费米子、高温超导体和其他强关联电子材料所表现出的不寻常性质提供了一把钥匙。这个提议涉及无序的作用，它如何改变“干净”材料的性质，以及发现一个可以表明无序何时重要的标准。这项工作的成功将对量子磁学领域和广泛的一类有趣和具有挑战性的材料产生广泛而直接的影响。这项工作对研究生和研究生教育产生更广泛的影响。这项工作还支持努力激发属于代表性不足群体的高年级学生对凝聚态物理学的兴趣，并向小学生推广，以激发下一代科学家的兴趣。

This award supports fundamental theoretical research and education in the area of quantum magnetism and the role of disorder in quantum magnets. The cuprate and heavy-fermion materials have phase transitions between magnetic and non-magnetic phases. Often, these phase transitions are driven by chemical substitution that also introduces disorder into the system. Depending on its nature and strength, disorder can lead to substantial changes in the critical behavior of magnetic systems. The PI aims to study of the effects of disorder and electronic dissipation on the critical behavior and collective excitations of quantum magnetic systems. Contrary to the classical problem with weak disorder, there is no established criteria for the relevance of disorder in quantum critical systems. The PI will search for the relevant criteria in quantum systems. Although there are an enormous number of systems in which critical behavior is modified by disorder, the PI will focus on the study of two experimentally relevant systems: the metallic f-electron alloy UCu5-xPdx where the so-called "non-Fermi liquid" (NFL) behavior has been observed, and the low-dimensional dilute insulating magnet La2Cu1-z(Zn,Mg)zO4. These systems have common features: (i) they can be tuned from a magnetically ordered phase to a paramagnetic phase through a quantum critical point (QCP) via chemical substitution; (ii) they have an anomalous magnetic behavior close to the QCP; (iii) they are disordered alloys. The PI will study these systems using modern field theoretical methods and compare the results with recent experimental data. These comparisons will serve as a filter for the development of the theory. Success of this work, involving developing criteria for disordered quantum magnets and the classification and elucidation of universal behavior, would have broad and direct impact on the area of quantum magnetism. This work has broader impacts in education at the graduate and postgraduate levels. This work also supports efforts to stimulate interest in condensed matter physics by advanced students belonging to underrepresented groups and outreach to elementary school students to stimulate the interest of the next generation of scientists.%%%This award supports fundamental theoretical research and education in the area of quantum magnetism and the role of disorder in quantum magnets. The PI will focus on chemical substitution and the effect of the disorder that often results on the properties of quantum magnets. Chemical substitution enables tuning through a quantum phase transition. Quantum phase transitions are distinct from classical phase transitions and are of great fundamental interest. They may provide a key to understanding unusual properties exhibited by heavy fermion, high temperature superconductors, and other strongly correlated electron materials. This proposal is concerned with the role of disorder, how it changes the properties of the "clean" materials, and the discovery of a criterion that can indicate when disorder is important. Success of this work would have broad and direct impact on the area of quantum magnetism and on a wide class of intriguing and challenging materials.This work has broader impacts in education at the graduate and postgraduate levels. This work also supports efforts to stimulate interest in condensed matter physics by advanced students belonging to underrepresented groups and outreach to elementary school students to stimulate the interest of the next generation of scientists.***