Resonant Ultrasound Studies of Complex Materials: Clathrates and Transition Metal Oxides

现代凝聚态物理学最令人兴奋的主题之一是在日益复杂的材料系统中发现和研究新现象和新形式的秩序。该计划的目标之一是研究新型复杂材料的弹性特性（即材料如何响应应变）。将研究两种复杂材料：过渡金属氧化物和所谓的包合化合物（具有笼状结构的化合物）。后者有望开发出更好的热电装置，这种装置不需要移动部件或含氯氟烃（CFC）的制冷剂就能将热转化为电（反之亦然）。这些复杂材料的弹性行为可能相当奇特，本研究计划将探索在多大程度上可以用最近发展的理论来理解这种行为。高年级本科生和研究生将在弹性性能和低温物理领域获得深入的经验，并掌握材料科学的各种技术技能。这一建议包括向系里的本科生开展外展活动。将特别努力帮助女学生。***技术摘要***本研究项目旨在系统研究复杂材料的弹性响应，包括过渡金属氧化物（TMOs）和包合物。将研究的材料处于凝聚态物理的前沿，包括层状钙钛矿钌酸盐Ca_(2-x)Sr_(x)RuO_(4)，三角形晶格化合物Na_(x)CoO_(2)，包合化合物YbFe_(4)Sb_（12）和ii型包合物Rb_(8)Na_(16)Si_（136）。共振超声光谱学将在2-400 K范围内常规使用，以获得弹性模量。在he3低温恒温器中进行脉冲回波和衰减测量。从科学上讲，有许多问题需要解决。其中一个问题涉及到包合物和结构玻璃之间的关系。具体来说，隧道状态是包合物所固有的吗？如果可以，可以识别隧道实体吗？另一个问题涉及结构-属性关系。各种结构特征在多大程度上可以用来预测材料的性能？TMOs的弹性性质是否可以用最近发展的涉及几何和其他类型挫折、纳米级相分离和量子临界性的思想来理解？高年级本科生和研究生将在弹性性能和低温物理领域获得深入的经验，并掌握材料科学的各种技术技能。这一建议包括向系里的本科生开展外展活动。将特别努力帮助女学生。

*** NON-TECHNICAL ABSTRACT ***One of the most exciting themes of modern condensed matter physics is the discovery and investigation of novel phenomena and new forms of order in materials systems of ever increasing complexity. It is one of the goals of the proposed program to study the elastic properties (i.e., how a material responds to strain) of novel, complex materials. Two kinds of complex materials will be studied: transition metal oxides and so-called inclusion compounds (compounds with a cage-like structure). The latter are promising for the development of better thermoelectric devices, which convert heat to electricity (and vice-versa) without moving parts or chloroflurocarbon (CFC)-containing refrigerants. The elastic behavior of these complex materials can be quite exotic, and this research program will explore to what extent the behavior can be understood with recently developed theories. Both senior undergraduate and graduate students will gain in-depth experience in the field of elastic properties and low temperature physics, and will acquire skills in various techniques in materials science. This proposal includes the development of outreach activities to undergraduate students in the department. Special efforts will be made to reach female students.*** TECHNICAL ABSTRACT ***This research program is designed to systematically study the elastic response of complex materials, including transition metal oxides (TMOs) and inclusion compounds. The materials that will be investigated are at the forefront of condensed matter physics and include the layered perovskite ruthenates Ca_(2-x)Sr_(x)RuO_(4), the triangular lattice compound Na_(x)CoO_(2), and inclusion compounds such as YbFe_(4)Sb_(12) and type-II clathrates such as Rb_(8)Na_(16)Si_(136). Resonant Ultrasound Spectroscopy will be routinely used from 2-400 K to obtain the elastic moduli. Pulse-echo and attenuation measurements in a He3-cryostat will be performed as appropriate. Scientifically, there are a number of issues that need to be resolved. One issue involves the relationship between inclusion compounds and structural glasses. Specifically, are tunneling states intrinsic to inclusion compounds? If so, can the tunneling entities be identified? Another issue involves structure-property relationships. To what extent can various structural features be used to predict the properties of the material? Can the elastic properties of TMOs be understood with recently developed ideas involving geometric and other types of frustration, nano-scale phase separation, and quantum-criticality? Both senior undergraduate and graduate students will gain in-depth experience in the field of elastic properties and low temperature physics, and will acquire skills in various techniques in materials science. This proposal includes the development of outreach activities to undergraduate students in the department. Special efforts will be made to reach female students.