Ultrafast Polar Topology Reversal via THz-Driven Inertial Switching

Topological polar structures in ferroelectric heterostructures offer functional states beyond ordinary domains. As polarization reversal underpins ferroelectric devices, switching between degenerate topological variants, which we refer to as topology reversal, would greatly expand the ways to control polar textures. However, polar topology reversal is challenging because it requires coordinated flipping of oppositely oriented local polarizations, a process not naturally driven by a uniform electric field. Using a multiscale modeling approach, we show that polar topology can be stabilized and reversed in a simple Pt/PbTiO$_3$/Pt nanocapacitor. Electrode-controlled boundary conditions drive tetragonal PbTiO$_3$ into competing orthorhombic- and rhombohedral-like polarization states, which form building blocks for diverse topological structures, including vortex arrays, skyrmion lattices, dipole spirals, and dipole waves. We further show that the same out-of-plane THz pulse can reversibly switch a double-$\mathbf q$ dipole wave between degenerate topological variants within a few picoseconds, while preserving its spatial modulation. This process is enabled by damping-assisted inertial switching, in which the THz pulse injects energy to drive large-angle polarization rotation across shallow barriers, while dissipation removes excess energy and traps the system in the reversed state. These results establish ferroelectric nanocapacitors as a simple platform for programmable polar topology and low-power, THz-speed control through dissipative dynamics.