Negative Thermal Expansion Near Structural Quantum Phase Transitions

非技术摘要：从人行道裂缝到冰山，热膨胀的影响可以在物理世界的各种环境中看到。虽然所有材料都具有这种基本性质，但绝大多数材料在受热时会膨胀。然而，最近新材料的发现揭示了负热膨胀（NTE）的情况，这是一种特殊的热诱导体积收缩现象。该团队最近观察到，当多个原子晶格结构在极低温度下稳定时，某些材料中会出现强NTE。这种情况是量子相变的一个例子，在不同的环境中经常观察到异常的材料行为。这项工作是追求利用物质的量子特性来推进技术和影响社会的普遍兴趣。研究采用多种实验技术，包括x射线散射和光谱学来测量在各种条件下表现出NTE的结构量子相变周围的磁和电子响应。该研究大量涉及从事与科学和教育相关的独立项目的本科生研究人员，同时获得在大学和国家实验室环境中的研究机会。物理学入门课程的新课程改革将涉及在波动力学层面教授的基本量子概念，同时大规模的新教育改革倡议开始推出。技术摘要：本奖项的研究活动旨在探索NTE材料的基础科学，并解决NTE与结构量子相变之间的明显联系。该奖项支持在选定的NTE材料中探索这种联系和不寻常的物理效应的广泛努力。主要的实验技术包括基于激光的光学实验，以产生和测量声脉冲，高分辨率非弹性x射线散射，以及选择NTE材料的单晶和粉末样品的磁化率，并在一些实验中结合低温应变控制。该项目的其他方面包括为本科生创造参与大学和国家实验室实验凝聚态研究的机会，以及与重新设计基于微积分的物理入门课程相关的物理教育研究的额外选择。分析了大规模实施新型工作室式物理教学的指标，以告知和指导最佳实践。此外，还为学生和学生开发了与NTE相关的动手演示工具。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-technical abstract: The effect of thermal expansion can be seen throughout the physical world in varied contexts, from sidewalk cracks to icebergs. While all materials exhibit this basic property, the vast majority of materials expand when heated. However, recent new material discoveries have revealed cases of negative thermal expansion (NTE), a peculiar phenomenon of heat-induced volume contraction. This team recently observed that strong NTE occurs in some materials when more than one atomic lattice structure is stable at very low temperatures. This circumstance is an example of a quantum phase transition, where anomalous material behavior is often observed in different contexts. This work is of general interest in the pursuit of exploiting quantum properties of matter to advance technology and impact society. Research pursued uses multiple experimental techniques including X-ray scattering and optical spectroscopy to measure magnetic and electronic responses under various conditions around structural Quantum Phase Transitions which exhibit NTE. The research heavily involves undergraduate researchers who pursue independent projects related to science and education while gaining exposure to research in both university and national lab settings. New curricular reform efforts in introductory physics courses will involve elementary quantum concepts taught at the level of wave mechanics while rollout of a massive new educational reform initiative commences.Technical abstract: The research activities of this award designed to explore the basic science of NTE materials and address the apparent connection between NTE and structural quantum phase transitions. This award supports a broad effort to explore this connection and unusual physical effects in select NTE materials. Primary experimental techniques include laser-based optical experiments to generate and measure sound pulses, high resolution inelastic X-ray scattering, and magnetic susceptibility on single crystals and powder samples of select NTE materials, incorporating low-temperature strain control in some experiments. Additional aspects of the project include creating opportunities for undergraduate student participation in university- and national laboratory-based experimental condensed matter research with additional options in physics education research related to a redesign of calculus-based introductory physics courses. Metrics for a massive implementation of a new studio-style physics teaching initiative are analyzed to inform and direct best practices. In addition, hands-on demonstration tools related to NTE are developed for students and by students.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.