Fig. 3: Comparing THz vibrational modes with DFT simulation.

a, b Low- and high-frequency background-subtracted measured SERS spectra (lines) compared to simulated Raman peaks (dashed and bars, omitting modes < 25 cm⁻¹, dashed curves are Gaussian broadened by 32 cm⁻¹). An exponential function has been fit and subtracted in (a) as described in Supplementary Note 4 (from data in Fig. 2a). c Extremal positions of the atoms of an oscillating BPT molecule (4) for a THz vibrational mode at 45 cm⁻¹ obtained with DFT (displacement amplified for visualisation). d Strongest measured THz modes compared to extracted gap thickness, as discussed in Supplementary Note 5 (colours as in (a)). Broad yellow lines show \(1/L\) dependence from Eq.(2). e Vibrational motions are described by how molecules interact with the Au facet.