Fig. 3.

Strong vibrational coupling for stacked Au nanoplates. a Transient absorption traces for stacked Au nanoplates probing on each single nanoplate and the overlapping area. The color lines are the fitting curves to the experimental data. The inset shows an optical image of the stacked Au nanoplates on carbon film. b Fast Fourier transform (FFT) spectra of the mechanical vibrations of the first plate f₁, second plate f₂, and the overlapping area. Mechanical coupling between the plates creates new frequencies f₊ and f₋. The vibration at ~20 GHz was ascribed to a mode that corresponds to motion of the two nanoplates relative to each other