Ultrafast nano-imagining of the photoinduced phase transition dynamics in VO$_{\mathrm{2}}$

ORAL

Abstract

Many quantum phase transitions in correlated matter exhibit spatial inhomogeneities with expected yet unexplored effects on the associated ultrafast dynamics. Here we demonstrate the combination of ultrafast non-degenerate pump-probe spectroscopy with scattering scanning near-field optical microscopy ($s$-SNOM) for ultrafast nano-imaging. In a femtosecond near-field non-degenerate near-IR (NIR) pump and mid-IR (MIR) probe experiment, we study the photoinduced insulator-to-metal (IMT) transition in nominally homogeneous VO$_{\mathrm{2}}$ micro-crystals using far-from equilibrium excitation. We observe spatial heterogeneity on 50-100 nm length scales in the fluence dependent IMT dynamics, ranging from sub-100 fs to 1 ps. With pump fluences as high as nominally 10 mJ/cm$^{\mathrm{2}}$ we can reach distinct excitation and saturation regimes. These results suggest a large sensitivity of the IMT with respect to local variations in strain, doping, or defects difficult to discern microscopically.

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Authors

  • Sven A. Doenges

    • Department of Physics, Department of Chemistry, and JILA, University of Colorado, Boulder, CO 80309

  • Omar Khatib

    • Department of Physics, Department of Chemistry, and JILA, University of Colorado, Boulder, CO 80309

  • Brian T. O'Callahan

    • Department of Physics, Department of Chemistry, and JILA, University of Colorado, Boulder, CO 80309

  • Joanna M. Atkin

    • Department of Chemistry, University of North Carolina, Chapel Hill, NC 27514

  • Jae Hyung Park

    • Department of Physics, University of Washington, Seattle, WA 98195

  • David H. Cobden

    • Department of Physics, University of Washington, Seattle, WA 98195

  • Markus B. Raschke

    • Department of Physics, Department of Chemistry, and JILA, University of Colorado, Boulder, CO 80309