Ultrafast infrared nano-imaging of far-from-equilibrium carrier and vibrational dynamics

REVIEWS AND HIGHLIGHTS	QUANTUM SCIENCE	MOLECULAR AND SOFT-MATTER	ULTRAFAST NANO-OPTICS AND NANOPHOTONICS	MINERALOGY AND GEOCHEMISTRY

Jun Nishida, Samuel C. Johnson, Peter T. S. Chang, Dylan M. Wharton, Sven A. Donges, Omar Khatib, and Markus B. Raschke
Nature Communications 13, 1083 (2022).
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Ultrafast infrared nano-imaging has demonstrated access to ultrafast carrier dynamics on the nanoscale in semiconductor, correlated-electron, or polaritonic materials. However, mostly limited to short-lived transient states, the contrast obtained has remained insufficient to probe important long-lived excitations, which arise from many-body interactions induced by strong perturbation among carriers, lattice phonons, or molecular vibrations. Here, we demonstrate ultrafast infrared nano-imaging based on excitation modulation and sideband detection to characterize electron and vibration dynamics with nano- to micro-second lifetimes. As an exemplary application to quantum materials, in phase-resolved ultrafast nano-imaging of the photoinduced insulator-to-metal transition in vanadium dioxide, a distinct transient nano-domain behavior is quantified. In another application to lead halide perovskites, transient vibrational nano-FTIR spatially resolves the excited-state polaron-cation coupling underlying the photovoltaic response. These examples show how heterodyne pump-probe nano-spectroscopy with low-repetition excitation extends ultrafast infrared nano-imaging to probe elementary processes in quantum and molecular materials in space and time.

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