American Chemical Society
nl3c02897_si_001.pdf (3.39 MB)

Optical Imaging of Ultrafast Phonon-Polariton Propagation through an Excitonic Sensor

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journal contribution
posted on 2023-10-18, 22:16 authored by Shan-Wen Cheng, Ding Xu, Haowen Su, James M. Baxter, Luke N. Holtzman, Kenji Watanabe, Takashi Taniguchi, James C. Hone, Katayun Barmak, Milan Delor
Hexagonal boron nitride (hBN) hosts phonon polaritons (PhP), hybrid light–matter states that facilitate electromagnetic field confinement and exhibit long-range ballistic transport. Extracting the spatiotemporal dynamics of PhPs usually requires “tour de force” experimental methods such as ultrafast near-field infrared microscopy. Here, we leverage the remarkable environmental sensitivity of excitons in two-dimensional transition metal dichalcogenides to image PhP propagation in adjacent hBN slabs. Using ultrafast optical microscopy on monolayer WSe2/hBN heterostructures, we image propagating PhPs from 3.5 K to room temperature with subpicosecond and few-nanometer precision. Excitons in WSe2 act as transducers between visible light pulses and infrared PhPs, enabling visible-light imaging of PhP transport with far-field microscopy. We also report evidence of excitons in WSe2 copropagating with hBN PhPs over several micrometers. Our results provide new avenues for imaging polar excitations over a large frequency range with extreme spatiotemporal precision and new mechanisms to realize ballistic exciton transport at room temperature.