Ultrafast nano-imaging of electronic coherence of monolayer WSe₂

Transition metal dichalcogenides (TMDs) have demonstrated a wide range of novel photonic, optoelectronic, and correlated electron phenomena for more than a decade. However, the effect of spatial heterogeneities on their exciton coherence dynamics with possibly long dephasing times is still poorly understood. Here, we image the coherent electron dynamics in monolayer WSe₂ using correlative adiabatic plasmonic nanofocused four-wave mixing (FWM) measurements. We resolve nanoscale heterogeneity on time scales ranging from less than 10 to greater than 45 fs at room temperature. We find a counterintuitive spatial anti-correlation between FWM and dephasing time which we interpret as a result of the impact of heterogeneous disorder on the spatial coherence of the nonlinear FWM polarization. These findings highlight the fundamental challenges caused by heterogeneities in TMDs and the resulting limits on photophysical properties.