Spectroscopy of Pressure- and Field-Induced Insulator-Metal Transitions: Exploring Charge- and Spin-Organization in Complex Oxides and Magnetic Semiconductors

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There is now strong evidence that some of the most scientifically interesting and technologically promising phenomena exhibited by correlated systems occur near low temperature phase boundaries. These phenomena include the spontaneous organization of mesoscale charge, spin, and orbital structures, and "colossal" sensitivities of physical properties to applied pressure and magnetic field. A better understanding of these exotic phenomena demands greater insight into how the low energy dynamical properties evolve across the low temperature phase transitions of these materials. This individual investigator award supports research that utilizes a unique method for using inelastic light scattering to spectroscopically explore - in a way not previously possible - the important evolution of the spin, charge, and lattice dynamics of correlated systems while pressure- and/or field-tuning through low temperature phase transitions. The principle focus of this study will be on two classes of phenomena: (A) Quantum phase transitions in complex oxides, to study the evolution and effects of spontaneous charge-, spin-, and orbital-organization near low temperature phase transitions. (B) Spin electronics in magnetic semiconductors, to explore the evolution and impact of magnetic cluster formation near phase transitions. Not only will this research afford critical information about the dynamics near various low temperature phase transitions of technologically important materials, but it will provide the scientific community a greater understanding of the limitations and benefits of applying low-temperature/high-pressure light scattering for studying phase transitions and extreme phase regimes in a variety of systems. Further, this project will train graduate student and postdoctoral researchers in cutting-edge pressure and spectroscopic techniques, eventually adding to the technical base of the country.Intensive recent research has uncovered a variety of functional materials exhibiting scientifically important phenomena with technologically promising properties, e.g., in magnetic storage devices, magnetic sensors, switches, etc. These exotic properties include extremely large sensitivities of the electrical properties to the application of magnetic fields ("colossal" magnetoresistance), and abrupt magnetic field- and pressure-sensitive transitions between electrically-conducting and -non-conducting phases. It is now believed that these exotic properties are likely caused by the spontaneous formation of nanometer-scale structures when these materials transition between conducting and non-conducting phases; however, the nature of this causal connection needs to be significantly elucidated before scientists can understand how best to design these materials for technological advantage. This individual investigator research project will utilize a unique method in which laser light is used to study how the magnetic-field- and pressure-dependent evolution of nanometer-scale structures give rise to the dramatic and technologically-useful properties in complex oxides and spin-electronic materials. The information that will be obtained with this project is an essential prerequisite to the effective design and utilization of these materials as devices. Further, this project will train graduate student and postdoctoral researchers in cutting-edge pressure and spectroscopic techniques, eventually adding to the important technical base of the country.