All-Optical Control of Interfacial Polarization in MoS2/WSe2 Heterobilayers.

All-optical tuning of van der Waals (vdW) heterostructures with coherent radiation offers a powerful strategy for manipulating interfacial electronic properties on femtosecond time scales. Using real-time time-dependent density functional theory, we predict a transient out-of-plane polarization in MoS2/WSe2 heterobilayers driven by intense ultrafast pulses. In the weak-field regime, the system preserves its intrinsic type-II band alignment, whereas at intermediate intensities, the field triggers a nonlinear enhancement of interlayer charge transfer. High-harmonic generation spectra undergo a crossover from the perturbative to the strong-field regime accompanied by the pronounced enhancement of a photoinduced interfacial dipole. At the highest intensities, interlayer polarization enhancement is sustained by massive field-driven spatial delocalization of electronic density into the vdW gap, promoted by localized charge saturation due to Pauli blocking. Lattice strain modifies the resonance conditions while preserving this strong-field polarization enhancement, establishing a microscopic mechanism for all-optical manipulation of interfacial dipoles at the ultrafast timescale.