Tunable factors and domain mechanisms for the negative dielectric permittivity of nanofilms in ultrafast time scale

The negative dielectric permittivity of nanofilms holds significant potential for the development of advanced devices. However, the regulatory mechanisms and microscopic origins of this phenomenon on ultrafast time scales remain inadequately understood. Therefore, we investigated the factors governing negative dielectric permittivity in ferroelectric nanofilms on ultrafast time scales and revealed the underlying microscopic mechanisms. A dynamic phase-field model was employed to simulate a BaTiO_3 nanofilm with a core-shell grain structure and analyze the effects of the damping coefficient, kinetic coefficient, and electric field amplitude. The results indicated that deviations of the damping coefficient from its optimal value weaken negative dielectric permittivity — lower values enhance positive permittivity, while higher values suppress domain evolution. The kinetic coefficient significantly affects the dielectric permittivity in the high-frequency range, and excessively large or small values tend to inhibit negative dielectric behavior. Larger electric field amplitudes shift the frequency range of negative permittivity toward higher frequencies. These results clarify the microscopic mechanisms underlying the relationship between parameter tuning and negative dielectric permittivity and provide critical insights into optimizing negative dielectric performance in ultrafast ferroelectric-based devices.