Fig. 3. Coherent oscillations of THz reflectivity without slow rise component.

(A) Normalized ${\mid \mathrm{\Delta }r(\mathrm{\omega },\mathrm{\tau })\mid }_{\text{osc}}^{\text{norm}}$ map with slow rise component subtracted. The vertical dashed line marks the LO phonon frequency at 3.7 THz, where a π phase flip occurs and above which a subsequent frequency chirp is evident. (B) Schematic dielectric energy loss function describing inelastic optical phonon scattering and screening function describing the renormalization of dressed charges for MAPI. (C) Fourier transformation along delay time axis τ, ${\mid \mathrm{\Delta }r(\mathrm{\omega },{\mathrm{\omega }}_{\text{osc}})\mid }_{\text{osc}}^{\text{norm}}$, showing an onset of a coherent beat between charge motion at ω and ω_LO.