Complex Behavior Near the Metal-Insulator Transition

Florida State University, Tallahassee FL

Investigators

Abstract

TECHNICAL SUMMARY This award supports theoretical and computational research and education on materials that are somewhere between metals and insulators. Material properties are easy to tune in this regime, where several possible ground states compete. Here most physical quantities display unusual behavior, and prove difficult to interpret using conventional ideas and approaches. Recent experiments reveal the significant effects of spatial inhomogeneities. In some cases, intermediate heterogeneous phases may emerge between the metal and the insulator, possibly even in absence of disorder. Such complexity emerges as a new paradigm of the metal-insulator transition region. The PI will carry out a comprehensive research program using advanced computational and theoretical techniques to advance understanding of fundamental physical processes in this regime, including: (1) the interplay of Mott and Anderson routes to localization, and the properties of electronic Griffiths phases preceding the metal-insulator transition; (2) the competition of Ruderman-Kittel-Kasuya-Yosida and Kondo singlets as a mechanism to suppress Fermi liquid coherence; (3) the role of the long-range Coulomb interaction and charge ordering, as a driving force for Wigner-Mott localization in doping-driven metal-insulator transitions. Methods based on dynamical mean-field theory and its extensions will be used to carry out the research. This project will train graduate students in theoretical and computational condensed matter physics. The PI will continue to promote and enhance scientific and technological understanding and importance of our research to the general public through outreach activities, including: presenting lectures at elementary schools in order to popularize science and technology, and to bring the most recent discoveries within reach of the youngest; acting as a Judge at annual Regional Science Fairs; and participating in the FSU Physics Department and the NHMFL Annual Open House activities. The PI will provide a leading role in developing a major new outreach initiative called the Emergent Labs which aims to take cutting-edge research discoveries in condensed matter science directly into the classrooms of middle and high school teachers. NONTECHNICAL SUMMARY This award supports theoretical and computational research and education on materials that are somewhere between metals and insulators. The PI will use advanced computational techniques to study materials which have electrons that interact strongly with each other and contain many imperfections in their structure or chemistry that are reflected in the environment of the electrons. Under certain conditions, increasing the number of defects and imperfections in a conducting material can turn it into an insulator. Recent experiments suggests that in some materials this is not a simple transformation, but rather the route from metal to insulator proceeds through complicated "bad metal" states. The PI will use advanced computational methods to investigate the nature of these states with an aim to understand the role of the strong interactions between electrons and how this transformation differs in bulk materials or in a single layer. This is fundamental research to understand the nature of metals, insulators, and new states of electronic matter that may exist between them. This research may contribute to the intellectual foundations of future device technologies and to developing new strategies to discover new materials with desired electronic properties. This project will train graduate students in theoretical and computational condensed matter physics. The PI will continue to promote and enhance scientific and technological understanding and importance of our research to the general public through outreach activities, including: presenting lectures at elementary schools in order to popularize science and technology, and to bring the most recent discoveries within reach of the youngest; acting as a Judge at annual Regional Science Fairs; and participating in the FSU Physics Department and the NHMFL Annual Open House activities. The PI will provide a leading role in developing a major new outreach initiative called the Emergent Labs which aims to take cutting-edge research discoveries in condensed matter science directly into the classrooms of middle and high school teachers.