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

Michigan State University, East Lansing MI

Investigators

Abstract

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.