Plasmon Damping Induced by Ferroelectric Phase Transition in a Single Plasmonic Nanocavity

Plasmon damping, the spectral line width of the plasmonic resonance, can be influenced by the charge transfer states at the metal-dielectric interface, known as chemical interface damping (CID). Construction of a metal-ferroelectric interface involving two-dimensional van der Waals ferroelectrics with a phase transition at the Curie temperature ( T C ), such as CuInP 2 S 6 (CIPS), is promising for the development of reconfigurable plasmonic devices. However, the effects of the ferroelectric phase transition on the plasmonic resonance at the interface, i.e., plasmon damping, remain elusive. Herein, we demonstrate the construction of an Au/CIPS/Au nanodisk-on-mirror (NDoM) nanocavity by embedding a ferroelectric CIPS flake in between a gold nanodisk and a gold nanoplate, with the plasmonic nanocavity dramatically strengthening light-matter interactions. The optical response of the Au/CIPS/Au nanocavity was enhanced by 37-fold in scattering in comparison with the corresponding Au/CIPS structure, which can be attributed to vertical plasmonic coupling in the nanocavity, boosting the intensity of the effective dipole moment of the radiation system. Variation of the plasmonic damping was observed during the CIPS ferroelectric phase transition, albeit with thermal hysteresis. Whereas a constant baseline of the damping was contributed by surface scattering, the damping induced by polarization was found to be proportional to the polarization intensity. When the temperature crossed T C, a steep increase of damping was observed, due to a variation of the CID induced by the CIPS phase transition. Optical sensitivity was evaluated to quantify the performance of NDoM nanocavities in a plasmonic device. This work provides a physical perspective toward understanding plasmon damping at metal/ferroelectric interfaces, as a pathway for the development of highly sensitive reconfigurable plasmonic devices.