Charge Fluctuations and Competing Orders in Strongly Correlated Materials

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Non-Technical Abstract:Electronic properties of many new materials with potentially great technological importance are dominated by interactions among charge carriers. Those correlations give rise to a variety of phenomena of current interest in condensed matter physics, including the emergence of novel states of matter. These effects are most pronounced near transitions between different phases - conductor to insulator, or superconductor to normal - that can be tuned by an external parameter, like magnetic or electric field. The underlying quantum nature of those transitions contributes to the complexity of the observed behaviors. This research addresses fundamental questions about the nature and the dynamics of several charge-ordered states in the presence of other, competing phases, especially in the vicinity of quantum phase transitions. Most of the experiments involve measurements of charge transport, including various time-dependent protocols, using either electric or extremely high magnetic fields to tune through the phase transitions in two-dimensional crystals and high-temperature superconductor materials. A key component of the project is education and training of a diverse group of young researchers for future careers in academia, national laboratories, and industry. It also incorporates various activities to broaden the participation of underrepresented groups in the areas of science, technology, engineering, and mathematics.Technical Abstract:Many unusual properties of strongly correlated materials have been attributed to the proximity of quantum critical points, where different types of orders compete and coexist, and may even give rise to novel phases. The role of collective fluctuations near quantum critical points is thus increasingly recognized as one of the key questions in the physics of strongly correlated systems. Even though fluctuations of various charge-ordered states have been of particular interest, e.g. to clarify their relationship with high-temperature superconductivity in cuprates, there have been few studies of charge, as opposed to spin, dynamics. The aim of the project is to bridge this gap by using time-resolved charge transport measurements on very long time scales, proven to be powerful probes of out-of-equilibrium or glassy charge dynamics, quantum critical points, and novel, intermediate phases. The research is designed to provide answers to several fundamental questions in condensed matter physics concerning the interplay of charge correlations and disorder, their relationship to high-temperature superconductivity, and the nature of various ground states and quantum critical points, such as the two-dimensional metal-insulator transition and the magnetic-field-tuned superconducting transition in cuprates. This knowledge is essential to the development of condensed matter subfields of strongly correlated materials and out-of-equilibrium phenomena.