Ultrafast Nanoimaging of Electronic Coherence of Monolayer WSe<sub>2</sub>.
basic_science · Level V
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- Record sourced from PubMed, PMID 36827496.
- Also identified by DOI 10.1021/acs.nanolett.2c04536.
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Abstract
Transition-metal dichalcogenides (TMDs) have demonstrated a wide range of novel photonic, optoelectronic, and correlated electron phenomena for more than a decade. However, the coherent dynamics of their excitons, including possibly long dephasing times and their sensitivity to spatial heterogeneities, are still poorly understood. Here we implement adiabatic plasmonic nanofocused four-wave mixing (FWM) to image the coherent electron dynamics in monolayer WSe<sub>2</sub>. We observe nanoscale heterogeneities at room temperature with dephasing ranging from <i>T</i><sub>2</sub> ≲ 5 to <i>T</i><sub>2</sub> ≳ 60 fs on length scales of 50-100 nm. We further observe a counterintuitive anticorrelation between FWM intensity and <i>T</i><sub>2</sub>, with the weakest FWM emission at locations of longest coherence. We interpret this behavior as a nonlocal nano-optical interplay between spatial coherence of the nonlinear polarization and disorder-induced scattering. The results highlight the challenges associated with heterogeneities in TMDs limiting their photophysical properties, yet also the potential of their novel nonlinear optical phenomena.