Infrared Resonance Tailoring of Individual Split‐Ring Resonators with Phase‐Change Materials by Locally Changing the Dielectric Surrounding of the Antenna Hotspots

For miniaturized active metasurfaces, resonance tuning of nanoantennas is a key ingredient. Phase‐change materials (PCMs) have been established as prime candidates for non‐volatile resonance tuning enabled by a change in the refractive index around nanoantennas. Conventionally, this tuning is induced by annealing the entire sample equally and does not allow changes on a meta‐atom level. Recently, it is demonstrated that individual rodantenna resonances can be adjusted by addressing each meta‐atom locally with precise laser pulses and switching the PCM there. However, simultaneously controlling several different modes remains elusive. In this work, PCM‐covered aluminum split‐ring resonators (SRRs) are switched locally to tune both the electric dipole resonances as well as the magnetic dipole resonances. By selectively switching the PCM at different hotspots of the SRRs, both resonances can be tuned individually. Finally, the field enhancement in the magnetic resonance allows continuous tuning of surface‐enhanced infrared absorption of native SiO 2 . This work serves as a proof of principle for sophisticated resonance tuning via changes in the refractive index at the hotspots of the selected antennas enabling fine‐tuning functionalities on a meta‐atom level and allows for post‐fabrication adjustments of metasurfaces.