****Technical Abstract**** Competing interactions in correlated electron materials lead to emergent phenomena, for example, phase transitions under external perturbations like temperature, chemical doping, and electric field. We will investigate metal-insulator phase transitions in oxides with strong interactions, for example, vanadium dioxide, and manganites with perovskite structure. We will primarily use infrared photons to document the evolution of the phase transformations at nanometer length scales and macroscopic length scales using broadband far-field and near-field infrared spectroscopy. The goal is to discover new paradigms that govern emergence in materials with strong interactions. Specifically, we hope to ascertain the role of size of the system on the evolution of metal-insulator phase transformations and accompanying structural instabilities. We plan to develop near-field nano-spectroscopy with broadband far-infrared photons in order to simultaneously document electronic and structural changes with about 10 nm spatial resolution. This experimental method will have wide applicability in physics, chemistry, biology, optical engineering and materials science that goes beyond the applications to correlated electron materials. This project will provide advanced scientific training for graduate and undergraduate students, and hence an excellent foundation for their future careers in academic institutions, and national and private research laboratories.
Strong interactions between a large number of electrons in solids lead to novel macroscopic behavior that is not seen in materials with weak interactions. Examples of such exotic macroscopic phenomena include metal-insulator phase transitions, superconductivity at high temperatures, and coupled magnetic, electronic and structural ordering. The principles of macroscopic organization do not follow in any simple manner from the known laws of physics that govern individual quantum entities (i.e. single electrons). The rules that regulate collective behavior and ordering phenomena in complex, interacting systems are yet to be discovered, and this is what motivates my research on such systems. We will primarily use infrared photons to investigate metal-insulator phase transitions and ordering phenomena in complex metal oxides. The photons interact with charged quantum particles and carry information about their behavior which we measure and record. Since organizational principles can vary with the size of the system, we plan to study metal-insulator phase transformations from nanometer length scales (hundreds of atoms) to macroscopic sizes (trillion trillion atoms). We plan to develop the experimental tool of near-field optical spectroscopy by coupling to a broad continuum of low energy infrared photons in order to study multi-faceted nanoscale phenomena. This project will provide advanced scientific training for graduate and undergraduate students, and hence an excellent foundation for their future careers in academic institutions, and national and private research laboratories.