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

这个凝聚态物理项目的重点是使用红外和光学光谱来研究强相关电子系统的动力学。从红外反射率测量中，我们可以得到电导率作为频率和温度的函数，这与两粒子电子相关函数有关，并为新型电子系统的表征提供了基本输入。随着工业向更高的速度、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。要研究的化合物类别包括Ruddlesden-Popper系列中的氧化钌，表现出或接近电子相变的镱化合物，以及掺杂的近藤半导体。通过研究与铜和锰两种过渡金属氧化物有关的钌酸盐，人们可以研究磁性与非常规电荷输运(例如：“不良金属行为”)。在我们的研究中，Yb化合物表现出包括重费米子和混合价现象的相图，以及等结构电子相变。对这些材料的研究可以帮助建立周期Anderson模型的力矩补偿物理和Mott-Hubbard系统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使用现代设备进行仔细的测量，并为研究生院和学术、工业或政府研究工作做好有价值的准备。这个凝聚态物理项目涉及强相关电子系统的表征。在这种材料中，电子之间的相互作用是非常强大的，可以诱发目前尚不清楚的电子现象。强电子相互作用还可以诱导物质的新相，并可以引导科学家们提出电子传递的新概念。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，并寻求结合新材料的解决方案，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，光谱测量红外，光学和紫外线的反射率将被用来获得电导率作为频率的函数。这样的测量可以揭示系统中的基本电子激发，包括氧化钌，它表现出新的输运和磁相；钇化合物，其电子价由整数变为非整数；硅化铁是一种能隙小的“近藤”半导体，在低频时具有很高的介电系数。参与这项研究的学生学会批判性地思考，并在现代设备上进行仔细的测量。对于本科生来说，这种经历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、工业或政府研究方面的职业准备。在大量未被充分代表的K-12学校的推广工作中，PI使用强相关系统（例如磁性和超导性）现象的演示来修饰研究、教育和科学职业的介绍。

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.