Bartenev, Alexander

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    Ultrafast optical spectroscopy of iron-based superconductors
    (2024-05-10) Bartenev, Alexander; Lysenko, Sergiy; College of Arts and Sciences - Sciences; Jiménez González, Héctor J.; Santana Colón, Samuel; Department of Physics; Arzuaga, Emmanuel
    This work is focused on the investigation of excited states dynamics of iron-based superconductors: FeSe0.8Te0.2 (type-11) and Ba(Fe0.92Co0.08)2As2 (type-122). We studied fluence-dependent non-equilibrium dynamics of thin superconducting films, unveiling transient response signal attributed to electron-electron, electron-phonon, and phonon-phonon interactions. The Two-Temperature Model (TTM) allowed us to quantify the constants of these processes, revealing a fluence-independent electron-phonon coupling constant for FeSe0.8Te0.2, in contrast to a fluence-dependent increase in Ba(Fe0.92Co0.08)2As2, suggesting light-induced stress as a potential underlying mechanism. Our findings indicate that the films undergo up to 1.3 GPa of light-induced stress within the surface layers of the thin films. During the initial 500 fs post-photoexcitation, stress is caused predominantly by the electron subsystem. Additionally, we observed coherent acoustic phonon generation and decay, determining the sound velocities for both materials. During the work we developed a femtosecond time-resolved pump-probe setup to study light-induced dynamics of iron-based superconductors. The system's automation was achieved through originally developed software, enabling autonomous data collection across various fluences and temperatures below 300 K. We employed a sophisticated analytical approach, combining the Two-Temperature Model (TTM) with a Runge-Kutta numerical solution and a grid search algorithm, to interpret the experimental data.