Ultrafast dynamics of a Moire-like Flux Closure phase of PbTiO₃/SrTiO₃ superlattices under terahertz excitation

Complex structural, electronic, and ferroelectric properties can emerge in PbTiO₃/SrTiO₃ superlattices on ultrafast timescale due to the coupling interaction of strain, polarization, and lattice distortion between the interacting layers. In this superlattice, we have observed a long-lived mesoscale ferroelectric order through photocarrier injection under low optical fluence. Here, we report the ultrafast time-domain dynamics of that emergent mesoscale Moire Flux Closure (MFC) phase under the excitation of terahertz pulses to delineate phononic and polarization dynamics coupling. This pump-probe experiment helps us identify the lattice interactions in the picosecond time scales and the interplay between collective and soft modes of the lattice. We have further identified the dispersive nature of both mesoscale and nanoscale orders within the MFC phase. We also investigated the coupling between mesoscale and collective modes.