CAREER: Investigation of Spatial and Temporal Scales of Cooperative Spin Clusters in Doped and Undoped Geometrically Frustrated Magnets

* 技术摘要 * 该提案是使用磁和空间和时间分辨光学技术相结合的几何阻挫磁系统的基本方面的调查。挫折的一个重要后果是形成自旋“保护体”的能力-与系统其余部分解耦的自旋集群。将研究的具体问题是：（a）化学无序的影响：孤立的自旋保护剂的形成归因于晶体结构中与空位相关的缺陷周围的成核。由化学无序（掺杂）引起的有意晶格畸变对阻挫的影响将被研究。（B）动力学：阻挫磁体中的自旋团簇在很宽的时间尺度上表现出波动，随温度和无序而变化。它们的系综动力学将被研究到皮秒以下的挫折行为的发生和发展，和（c）相关长度：集群大小的保护基的挫折改变了能源景观和自旋相关长度的变化。这些保护国的形成和演变将被研究。这项研究将结合联合收割机在不同领域（光学，磁学和低温物理学）的流行技术，其结果将导致理解新的自旋相关现象，以及影响它们的因素，在复杂的合作磁体。* 非技术性摘要 * 挫折是一个系统无法达到一个独特的基态。它在各种各样的系统中起着重要的作用，从蛋白质折叠到纳米簇的形成。一组有趣的系统是具有独特晶格对称性的磁性化合物，其中磁自旋在几何上受到挫折。这一建议将带来一个新的视角，通过调查的基本方面，使用磁和高分辨率的光学技术相结合的几何挫折磁系统的研究。将特别强调与挫折感的发生和发展有关的空间和时间尺度的测量。光学探针的使用将允许第一次直接测量受挫系统中的自旋动力学，并将能够访问任何其他现有技术无法达到的时间和长度尺度。这些结果将导致对受挫系统中观察到的复杂集体行为的一般性见解，这些系统应该适用于各种领域，如量子计算和信息处理。由于加州大学默塞德位于中央谷的中心，为吸引和留住代表性不足的学生提供了一种手段，这项建议将通过组建一个专注于科学和工程的妇女小组，加强少数群体，特别是妇女对尖端研究的参与。它还将导致一个“发现为导向”的实验室课程，特别强调凝聚态和纳米科学的本科和研究生物理课程的主题的发展。

*** Technical Abstract ***This proposal is an investigation of the fundamental aspects of geometrically frustrated magnetic systems using a combination of magnetic and spatially and temporally-resolved optical techniques. An important consequence of frustration is the ability to form spin 'protectorates'-spin clusters that are decoupled from the rest of the system. The specific issues that will be investigated are: (a) Effect of chemical disorder: The formation of isolated spin protectorates is attributed to nucleation around vacancy-related defects in the crystal structure. The effects of intentional lattice distortion induced by chemical disorder (doping) on frustration will be investigated, (b) Dynamics: Spin clusters in frustrated magnets exhibit fluctuations over a broad range of time scales, varying with temperature and disorder. Their ensemble dynamics will be investigated down to picoseconds to follow the onset and development of frustrated behavior, and (c) Correlation length: The cluster size of the protectorates changes substantially as frustration alters the energy landscape and the spin correlation lengths. The formation and evolution of these protectorates will be studied. This research will combine techniques prevalent in distinct fields (optics, magnetism, and low temperature physics) and the results will lead to the understanding of novel spin related phenomena, and the factors that influence them, in complicated cooperative magnets. *** Non-technical Abstract ***Frustration is the inability of a system to reach a unique ground state. It plays an important role in a wide variety of systems, ranging from protein folding to the formation of nanoclusters. An intriguing set of such systems is magnetic compounds with unique lattice symmetries where the magnetic spins are geometrically frustrated. This proposal will bring a new perspective to the study of geometrically frustrated magnetic systems via the investigation of their fundamental aspects using a combination of magnetic and high-resolution optical techniques. Particular emphasis will be given to the measurement of spatial and temporal scales relevant to the onset and development of frustration. The use of optical probes will allow the first direct measurement of spin dynamics in frustrated systems, and will be able to access time and length scales unattainable by any other existing techniques. The results will lead to general insights into the complicated collective behavior observed in frustrated systems that should be applicable to a variety of fields, such as quantum computing and information processing. Since the location of UC Merced at the heart of the Central Valley offers a means to attract and retain underrepresented students to science and technology, this proposal will enhance participation of minority groups, particularly women, in cutting-edge research through the formation of a focused Women in Science and Engineering group. It will also lead to the development of a 'discovery-oriented' laboratory course with special emphasis on topics of condensed matter and nanoscience for both undergraduate and graduate physics curriculum.