Investigation of optically-driven supercondcutors using pump-probe Raman scattering

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Non-Technical Abstract Superconductivity is characterized by a complete loss of electrical resistance. It is a quantum state that arises out of strong interactions of electronic charges and orbitals, magnetism, and vibrations of atoms. The specific mechanisms in many materials are puzzling to scientists. This project takes advantage of a recently developed experimental technique, pump-probe Raman spectroscopy, to investigate superconductivity in so-called transient states. These occur right after a very short laser pulse hits the material and either kicks some electrons out of their orbits or induces large amplitude vibrations of the atoms. The material can briefly go into a different transient state, e.g., a superconductor will lose superconductivity, or the opposite can happen – superconductivity may arise in a material that does not exhibit it under normal circumstances. Time-resolved Raman scattering creates a movie of how these states develop and how they come back to the original state. The main idea behind this project is to make such movies of superconductors to reveal otherwise hidden quantum processes. This knowledge is used to test ideas about mechanisms of superconductivity and helps to harness superconductors for practical applications. The work is carried out at the ultrafast laser spectroscopy laboratory at the University of Colorado-Boulder built with the funds provided earlier by the National Science Foundation. The project contributes to the education and training of graduate and undergraduate students.Technical AbstractThis project focuses on groundbreaking measurements of superconductors shortly after absorption of an ultrashort laser pulse. The purpose is to experimentally investigate still enigmatic mechanisms of equilibrium superconductivity in copper oxides as well as the general phenomenon of light-induced nonequilibrium superconductivity. In the experiments, the investigated sample is driven out of equilibrium by a short laser pulse, and Raman scattering from another time-delayed pulse will probe its relaxation. These experiments track time-evolution of phonons, electronic temperature, and the superconducting gap as the system thermalizes. This novel approach elucidates energy flows, transient timescales, and heating in optically-driven superconductivity recently reported in intercalated C60 and some copper oxides. Nonlinear phononics and Josephson current-based mechanisms suggested as explanations of this phenomenon are tested. Advances in this area will ultimately underlie development of new materials and devices involving optical control of superconductivity. The work is carried out at the ultrafast laser spectroscopy laboratory at the University of Colorado-Boulder built with the funds provided previously by National Science Foundation. The project contributes to the education and training of graduate and undergraduate students.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.