Direct in situ observation of the percolation transition in VO2 thin film by peak-shift spectroscopy

When a thin film undergoes a percolative insulator-to-metal phase transition, the real part of the dielectric constant dramatically changes; it diverges close to the percolation threshold and becomes negative in the metallic phase. To date, the percolative nature of this phase transition has been monitored by near-field imaging or conventional spectroscopy. Although such methods are successful, they require laborious raster scanning or complicated theoretical fitting processes. In this study, using the strong coupling between slot antennas and a phase-transition material, a direct step-by-step investigation of the percolation transition can be demonstrated without any scanning or fitting processes. The percolation threshold can be identified in real time by monitoring the peak position, because the resonance transmission through the slot antenna array is highly affected by the dielectric environment. The work presented in this study could potentially contribute to the characterization of phase-transition materials to be used in memory devices or active metamaterials.