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

这个凝聚态物理学项目的重点是使用红外和光学光谱学来研究强相关电子系统的动力学。从红外反射率测量可以获得电导率作为频率和温度的函数，这涉及到两个粒子的电子相关函数，并提供了基本的输入，以表征新的电子系统。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，强相关系统与技术的相关性也在增加。待研究的化合物类别包括Ruddlesden-Popper系列中的钌氧化物，表现出或接近电子相变的镱化合物，以及掺杂的Kondo半导体。通过研究与铜酸盐和过渡金属氧化物相关的铁酸盐，人们可以研究磁性和非常规电荷传输（例如“坏金属行为”）之间的关系。在我们的研究中的Yb化合物表现出的相图，包括重费米子和混合价现象，以及同构的电子相变。对这些材料的研究有助于建立周期性安德森模型的矩补偿物理学与Mott-Hubbard系统的相变动力学之间的联系。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，并为研究生院和学术，工业或政府研究就业做好宝贵的准备。这个凝聚态物理项目涉及强关联电子系统的表征。在这样的材料中，电子之间的相互作用非常强大，并且可以诱导尚未理解的电子现象。强电子相互作用也可以诱导物质的新相，并可以引导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：随着工业向更高的速度和更小的尺寸发展，并寻求采用新材料的解决方案，来自强相关系统研究的知识库变得越来越重要。在这项研究中，红外，光学和紫外线反射率的光谱测量将被用来获得电导率作为频率的函数。这种测量可以揭示系统中的基本电子激发，包括氧化钌，其表现出新颖的传输和磁相;镱化合物，其表现出相变，在该相变处电子价从整数值变为非整数值;以及硅化铁，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考，并对现代设备进行仔细测量。对于本科生来说，这种经验为研究生院提供了宝贵的准备;对于研究生来说，这种培训增强了他们在教学，工业或政府研究中的职业生涯的准备。 在K-12学校的推广工作中，学生人数严重不足，PI使用强相关系统（例如磁性和超导性）的现象演示来美化研究和教育以及科学职业的演示。

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.