Figure 3. Ultrafast time-resolved exciton dynamics of coherently/randomly stacked bilayers.

(a) Top panel: comparison of transient dynamics of interlayer excitons in coherently stacked and randomly stacked bilayers. Both bilayers are pumped by the same laser fluence of 24 μJ cm⁻², and measured at the same probe photon energy of 1.6 eV. Bottom panel: intralayer exciton dynamics of MoS₂ (blue, 1.87 eV) and WS₂ (red, 1.96 eV) measured in the coherently stacked bilayer with the same pump fluence of 24 μJ cm⁻². (b) The pump-fluence-dependent maximum ΔT/T₀ of the coherently stacked bilayer. (c) Spectrally resolved ΔT/T₀ at the direct interlayer exciton state of ∼1.6 eV (the dashed line) is shown. The data are measured at Δt≈0 ps with a pump fluence of 32 μJ cm⁻². (d) Schematic illustration of a pump-induced exciton transient as a function of pump–probe delay Δt (from left to right). Immediately after the 3.1-eV pump excitation (left), electrons are rapidly transferred in MoS₂ and holes are rapidly transferred in WS₂ (middle). Then the interlayer recombination is measured by setting the probe photon energy of 1.6 eV (right).