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Structural imaging of nanoscale phonon transport in ferroelectrics excited by metamaterial-enhanced terahertz fields

  • Author(s): Zhu, Y;
  • Chen, F;
  • Park, J;
  • Sasikumar, K;
  • Hu, B;
  • Damodaran, AR;
  • Jung, IW;
  • Highland, MJ;
  • Cai, Z;
  • Tung, IC;
  • Walko, DA;
  • Freeland, JW;
  • Martin, LW;
  • Sankaranarayanan, SKRS;
  • Evans, PG;
  • Lindenberg, AM;
  • Wen, H
  • et al.
Abstract

Nanoscale phonon transport is a key process that governs thermal conduction in a wide range of materials and devices. Creating controlled phonon populations by resonant excitation at terahertz (THz) frequencies can drastically change the characteristics of nanoscale thermal transport and allow a direct real-space characterization of phonon mean-free paths. Using metamaterial-enhanced terahertz excitation, we tailored a phononic excitation by selectively populating low-frequency phonons within a nanoscale volume in a ferroelectric BaTiO3 thin film. Real-space time-resolved x-ray diffraction microscopy following THz excitation reveals ballistic phonon transport over a distance of hundreds of nm, two orders of magnitude longer than the averaged phonon mean-free path in BaTiO3. On longer length scales, diffusive phonon transport dominates the recovery of the transient strain response, largely due to heat conduction into the substrate. The measured real-space phonon transport can be directly compared with the phonon mean-free path as predicted by molecular dynamics modeling. This time-resolved real-space visualization of THz-matter interactions opens up opportunities to engineer and image nanoscale transient structural states with new functionalities.

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