Probing the Electronic State of Novel Materials using the Local Atomic Structure

这个凝聚态物理项目专注于使用红外和光学光谱来研究强关联电子系统的动力学。从红外反射率测量可以得到电导率作为频率和温度的函数，它与两粒子电子关联函数有关，并为新型电子系统的表征提供了基本输入。随着工业朝着更高的速度、更小的尺寸和采用新材料的解决方案发展，强关联系统与技术的相关性越来越大。将要研究的化合物类别包括Ruddlesden-Popper系列中的Ru氧化物，呈现或接近电子相变的Yb化合物，以及掺杂的近藤半导体。通过研究与铜酸盐和锰酸盐过渡金属氧化物有关的Ruthenate，可以研究磁性与非常规电荷传输(例如，“不良金属行为”)之间的关系。我们研究的Yb化合物的相图包括重费米子现象和混合价现象，以及等结构的电子相变。对这些材料的研究有助于在周期Anderson模型的力矩补偿物理和Mott-Hubbard系统的相变动力学之间建立联系。参与这项工作的本科生和研究生学习利用现代设备进行仔细的测量，并为研究生学习和在学术、工业或政府研究中就业做有价值的准备。%这个凝聚态物理项目涉及强关联电子系统的表征。在这种材料中，电子之间的相互作用非常强大，可以诱导出尚未被理解的电子现象。强烈的电子相互作用也可以诱导新的物质相，并可能导致科学家对电子传输的新概念。这些材料将在新兴技术中发挥越来越重要的作用：随着工业向更快的速度和更小的尺寸发展，并寻求包含新材料的解决方案，来自强关联系统研究的知识库变得越来越重要。在这项研究中，将使用红外、光学和紫外线反射率的光谱测量来获得作为频率函数的电导率。这种测量可以揭示系统中的基本电子激发，其中包括显示出新的输运和磁相的Ru氧化物；表现出电子价态从整数值到非整数值的相变的Yb化合物；以及硅化铁，这是一种小能隙“近藤”半导体，在低频下具有非常高的介电系数。参与这项研究的学生学习批判性思维，并在现代设备上进行仔细的测量。对于本科生来说，这一经历为研究生提供了宝贵的准备；对于研究生来说，这种培训增强了他们在教学、工业或政府研究领域的职业准备。在人口比例严重偏低的K-12学校的外联工作中，国际学生联合会利用强相关系统(例如磁学和超导)现象的演示来美化关于研究和教育以及科学职业的陈述。

This condensed matter physics project focuses on the use of infrared and optical spectroscopy to study the dynamics of strongly correlated electron systems. From infrared reflectivity measurements one can obtain conductivity as a function of frequency and temperature, which relates to the two-particle electronic correlation function and provides fundamental input to the characterization of novel electronic systems. As industry moves toward higher speeds, smaller sizes and solutions incorporating novel materials, the relevance of strongly correlated systems to technology increases. Compound classes to be studied include ruthenium oxides in the Ruddlesden-Popper series, ytterbium compounds that exhibit or are close to an electronic phase transition, and doped Kondo semiconductors. By studying ruthenates, which are related to both cuprate and manganate transition-metal oxides, one can investigate the relationship between magnetism and unconventional charge transport (e.g. "bad metal behavior"). The Yb compounds in our research exhibit a phase diagram that includes heavy-fermion and mixed-valence phenomena, as well as an isostructural electronic phase transition. Research on these materials can help forge a link between the moment compensation physics of the periodic Anderson model and the phase transition dynamics of Mott-Hubbard systems. Undergraduate and graduate students involved in this work learn to carry out careful measurements utilizing modern equipment and receive valuable preparation for graduate school and employment in academic, industrial or government research.%%%This condensed matter physics project involves the characterization of strongly correlated electron systems. In such materials, interactions between electrons are very powerful and can induce electronic phenomena which are not yet understood. Strong electronic interactions can also induce new phases of matter and can lead scientists to new concepts of electron transport. These materials will play an increasingly significant role in emerging technologies: as industry moves toward higher speeds and smaller sizes and seeks solutions incorporating novel materials, the knowledge base from studies of strongly correlated systems becomes increasingly relevant. In this research, spectroscopic measurements of infrared, optical and ultra-violet reflectivity will be used to obtain conductivity as a function of frequency. Such measurements can reveal the fundamental electronic excitations in systems, including ruthenium oxides, which exhibit novel transport and magnetic phases; Ytterbium compounds, which manifest a phase transition at which the electronic valence changes from integer to non-integer values; and iron silicide, a small energy gap "Kondo" semiconductor with a very high dielectric coefficient at low frequency. Students involved in this research learn to think critically and to carry out careful measurements on modern equipment. For undergraduates this experience provides valuable preparation for graduate school; for graduate students, this training enhances their preparation for a career in teaching, industry or government research. In outreach efforts at K-12 schools with substantial underrepresented populations, the PI uses demonstrations of the phenomena of strongly correlated systems (e.g. magnetism and superconductivity) to embellish presentations on research and education and careers in science.