Disordered Critical Quantum Magnetic Systems

该奖项支持量子磁学和无序在量子磁体中的作用领域的基础理论研究和教育。铜酸盐和重费米子材料在磁相和非磁相之间有相变。通常，这些相变是由化学取代驱动的，化学取代也会给系统带来无序。根据无序的性质和强度，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。与经典的弱无序问题相反，在量子临界系统中，无序的相关性没有既定的标准。PI将在量子系统中搜索相关标准。尽管有大量系统的临界行为被无序改变，但PI将专注于两个实验相关系统的研究：金属f电子合金UCu5-xPdx，其中观察到了所谓的“非费米液体”(NFL)行为，以及低维稀磁绝缘磁体La2Cu1-z(锌，镁)氧化锌。这些系统有共同的特点：(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)它们在QCP附近具有反常的磁行为；(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。这些比较将成为该理论发展的过滤器。这项工作的成功，包括制定无序量子磁铁的标准，以及对普遍行为的分类和阐明，将对量子磁学领域产生广泛和直接的影响。这项工作对本科生和研究生的教育有更广泛的影响。这项工作还支持努力激发属于代表性不足群体的高级学生对凝聚态物理的兴趣，并向小学生推广，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，以及无序在量子磁铁中的作用。PI将专注于化学取代和经常导致量子磁铁性质的无序的影响。化学替代使调谐可以通过量子相变来实现。量子相变不同于经典相变，具有重要的基础性意义。它们可能为理解重费米子、高温超导体和其他强相关电子材料所表现出的不同寻常的性质提供了关键。这项提议涉及无序的作用，无序如何改变“干净”材料的性质，以及发现一种可以指示无序何时重要的标准。这项工作的成功将对量子磁学领域以及一大类有趣和具有挑战性的材料产生广泛和直接的影响。这项工作对研究生和研究生教育有更广泛的影响。这项工作还支持努力激发属于代表性不足群体的高级学生对凝聚态物理的兴趣，并向小学生进行宣传，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.***