Fig. 4: Ultrafast dynamics and density-dependent energy renormalization of hybridized excitons.

a Pump-induced change of the mid-infrared electric field ΔE as a function of the pump-probe delay time t_pp recorded at fixed electro-optic sampling time t_eos = 0 fs for different twist angles θ (spheres). Curves are vertically offset for clarity. The dashed lines represent fits to the data with an exponential decay. b Exciton decay time τ as a function of the twist angle θ, determined by the decay constant of the fit in a. The error bars indicate one standard deviation. c 1s–2p resonance energy ħω_res for different pump fluences Φ at a pump-probe delay time t_pp = 5.1 ps recorded for twist angles θ = 0°, 5°, and 60°, respectively (spheres). The resonance energies were extracted from the dielectric response by fits to a phenomenological model (see Supplementary Fig. 5). The blue circle marks the resonance energy derived from the microscopic theory shown in Fig. 2c. The sample was kept at a temperature of 5 K. The error bars represent the 95% confidence interval of the fitting procedure. d Calculated probability density of the electron within the two layers for a hybrid exciton for twist angles θ = 60°, 50°, and 0°, where the hole is chosen to remain at a fixed position in the top layer.