Inelastic Light Scattering as a Probe of Electronic Correlations

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NON-TECHNICAL SUMMARY This award supports theoretical research and educational activities on a class of materials in which electrons interact strongly. Many of these materials become superconducting at sufficiently low temperature. The phenomenon of superconductivity is signaled by the conduction of electricity without energy loss. If materials can be discovered that exhibit superconductivity at sufficiently high temperature, then they could be used for the transmission of electrical power. This award supports research geared toward deeper understanding of the role of correlations in electron motion that arise from strong electron interaction in a family of superconducting materials which contain the element iron in their chemical composition. These materials may be stepping stones to developing new materials which exhibit superconductivity at higher temperatures, perhaps reaching up to room temperature. The PI will develop theory to understand the implications of data obtained from experiments in which light is scattered off iron-based superconductors. Strong interactions between electrons cause the state of each electron to be determined by the motion of all other electrons. The resulting electron-electron interactions cause the electrons to self-organize and cause them to respond collectively to external stimuli. The PI and his research team will study collective behavior that arises in the broad class of iron-based superconductor materials. The PI will focus on the interplay of three types of electronic self-organization: superconductivity, magnetism, and structural order. While the individual electrons in ordinary metallic conductors lose their energy through interaction with material imperfections leading to losses, the collective flow characteristic of superconductors is rigid and cannot be easily disrupted leading to loss free transmission of electricity. Magnetism appears when the microscopic elementary magnets inside the solid all point in the same direction setting the north pole of a magnet. Structural ordering is caused by the electrons preferring a specific propagation direction. The PI will carry out a comprehensive study of all these collective phenomena within a single theoretical framework.The research will have a broad impact on the scientific community and the public through conferences and journal publications, and through an existing outreach program to school children. The PI will further design university courses that incorporate modern developments in theoretical physics to train the next generation. This award will support and contribute to the training and education of graduate students seeking their PhD degrees in theoretical condensed matter physics. TECHNICAL SUMMARYThis award supports theoretical research and educational activities with the goal of advancing understanding of the collective behavior of electrons in iron-based superconductors and low-dimensional electronic materials. The PI will focus on collective phenomena in iron-based superconductors probed by light. As the collective phenomena are the fingerprints of ordering, the PI will investigate the structure and interplay of order parameters, and closely related questions of the mechanism of superconductivity and possible symbiotic relationships among magnetism, lattice deformation and superconductivity. The major objective of the proposed research is to advance understanding of collective behavior emergent at the onset of different macroscopic orders, and the interplay and the competition among ordered states. The PI aims to advance analytical techniques for describing correlation effects and collective response of layered superconductors and interacting electron liquids. A variety of standard modern methods will also be used in the research. The PI aims to contribute to the understanding of universal aspects of symmetry breaking at the onset of classical and quantum phase transitions. This project also includes a study of spin transport in low dimensional systems. The collective behavior in these systems sets in due to the interaction-induced self-organization of microscopic fields felt by individual electrons. The PI will investigate enhancement of electronic quantum coherence as shown by sharp modes in Raman spectra and the ways in which correlations affect the electron dynamics.The research will have a broad impact on the scientific community and the public through conferences and journal publications, and through an existing outreach program to school children. The PI will further design university courses that incorporate modern developments in theoretical physics to train the next generation. This award will support and contribute to the training and education of graduate students seeking their PhD degrees in theoretical condensed matter physics.