Fig. 4. Time-dependent mean-field model.

(A and B) Response function of the order parameter for the microscopic two-band model on the 1D lattice with purely excitonic behavior (A) and in the presence of electron-phonon coupling (B). The coupling is small with respect to the Coulomb interaction and explicitly breaks the continuous symmetry of the system. (C) Spatial and temporal evolution of the phonon displacement, δX, for the case of nonzero electron-phonon coupling following an excitation at the center of the system at time t = 0, calculated within the mean-field description. (D to F) Windowed FT of the results in (C) at specified lattice sites, where Δr indicates the distance from the center of the excitation area. The red and orange dashed lines indicate the bare phonon frequency used in these calculations and the size of the phase mode gap, respectively. The bandwidth of the conduction and valence bands is set to 1.6 eV and the Coulomb interaction to 0.84 eV. The corresponding bandgap is about 0.32 eV.