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Optical Control of Non-Equilibrium Phonon Dynamics

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journal contribution
posted on 24.06.2019 by Aravind Krishnamoorthy, Ming-Fu Lin, Xiang Zhang, Clemens Weninger, Ruru Ma, Alexander Britz, Chandra Sekhar Tiwary, Vidya Kochat, Amey Apte, Jie Yang, Suji Park, Renkai Li, Xiaozhe Shen, Xijie Wang, Rajiv Kalia, Aiichiro Nakano, Fuyuki Shimojo, David Fritz, Uwe Bergmann, Pulickel Ajayan, Priya Vashishta
The light-induced selective population of short-lived far-from-equilibrium vibration modes is a promising approach for controlling ultrafast and irreversible structural changes in functional nanomaterials. However, this requires a detailed understanding of the dynamics and evolution of these phonon modes and their coupling to the excited-state electronic structure. Here, we combine femtosecond mega-electronvolt electron diffraction experiments on a prototypical layered material, MoTe2, with non-adiabatic quantum molecular dynamics simulations and ab initio electronic structure calculations to show how non-radiative energy relaxation pathways for excited electrons can be tuned by controlling the optical excitation energy. We show how the dominant intravalley and intervalley scattering mechanisms for hot and band-edge electrons leads to markedly different transient phonon populations evident in electron diffraction patterns. This understanding of how tuning optical excitations affect phonon populations and atomic motion is critical for efficiently controlling light-induced structural transitions of optoelectronic devices.

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