EAGER: SUPER: Experimental characterization of microscopic properties of superconducting polyhydrides; towards a realistic theoretical framework for warm superconductivity

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NON-TECHNICAL DESCRIPTION: Superconductors perfectly transmit electricity and exclude magnetic fields. The remarkable properties of superconductors allow lossless energy transmission, design of magnetically levitating devices, and are key to quantum computation technology. Superconductor-based technology relies on discovery of superconducting materials that operate at conditions close to ambient, which remains an unsolved challenge. Superconductivity at room temperature was recently discovered in hydrogen-rich materials albeit at extremely high pressures. To find room-temperature superconductors with lower critical pressure, an accurate theoretical model with predictive power is required. However, experimentally, the warm superconducting state is insufficiently characterized at microscopic level to fully constrain the theoretical models. This project aims to tackle this issue with the aid of novel spectroscopic tools that overcome inherent difficulties of characterization of materials at high pressures. By maintaining a feedback loop between experiment and theory, the project will lead to the development of a robust framework for understanding warm superconductivity and a model with predictive power for direct technological applications. The project will train students in cutting-edge science who are competent in both experiment and theory, have vision to think out of the box to explore the new frontiers and lead the next generation of scientific discoveries. TECHNICAL DESCRIPTION: Warm superconducting states in polyhydrides have been discovered under extreme pressures, reached exclusively in diamond anvil cells. The majority of characterizations of warm superconducting states, like magnetic susceptibility and electrical resistivity, are being made with the goal of detecting the onset of the superconductivity. These measurements are however insufficient to fully constrain the theoretical models and set limitations on the predictive power of the theories towards reaching an ambient-conditions superconductor. Two essential parameters for constraining the theoretical models are the superconducting gap and the electron-phonon coupling constant near the superconducting transition. Unlike ambient pressure superconductors, however, the geometry and size of a diamond anvil cell, limits the types of applicable characterization methods. In this project, spectroscopic methods including electronic Raman spectroscopy and ultrafast pump-probe measurements advanced in the PI's laboratory are used with the goal of systematic characterization of the superconducting states of polyhydride superconductors and determination of the fundamental parameters. Parallel theoretical analysis and modeling will allow approaching a realistic microscopic model for superconductivity of polyhydrides and theory-guided discovery of ambient-conditions superconducting materials. This project will advance experimental and theoretical understanding of warm superconductivity and its application in technology. Students receive training in cutting-edge experimental and theoretical techniques and participate in a research program that provides them with a rich experience in scientific method and connection between theory and observations.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.