For miniaturized active nanophotonic components like adjustable lenses, resonance tuning of nanoantennas is essential. Phase-change materials (PCMs) have been established as prime candidates for nonvolatile resonance tuning based on a change in the refractive index. Currently, a novel material class of switchable infrared plasmonic PCMs, like In 3 SbTe 2 (IST), is emerging. Because IST can be locally optically switched between dielectric (amorphous) and metallic (crystalline) states, it becomes possible to directly change the geometry and shape of nanoantennas to tune their infrared resonances. Here, crystalline IST split-ring resonators (SRRs) are directly optically written and reconfigured to continuously tune their magnetic dipole resonance wavelengths from 10.6 to 8.2 μm without changing their electric dipole (ED) resonances. The SRRs are further modified into crescents and J-antennas, displaying electric quadrupole and rotated ED modes, respectively. Our concepts may be well suited for rapid prototyping, speeding up workflows for engineering ultrathin, tunable, plasmonic devices for infrared nanophotonics.

In tetralayer graphene, three inequivalent layer stackings should exist; however, only rhombohedral (ABCA) and Bernal (ABAB) stacking have so far been observed. The three stacking sequences differ in their electronic structure, with the elusive third stacking (ABCB) being unique as it is predicted to exhibit an intrinsic bandgap as well as locally flat bands around the K points. Here, we use scattering-type scanning near-field optical microscopy and confocal Raman microscopy to identify and characterize domains of ABCB stacked tetralayer graphene. We differentiate between the three stacking sequences by addressing characteristic interband contributions in the optical conductivity between 0.28 and 0.56 eV with amplitude and phase-resolved near-field nanospectroscopy. By normalizing adjacent flakes to each other, we achieve good agreement between theory and experiment, allowing for the unambiguous assignment of ABCB domains in tetralayer graphene. These results establish near-field spectroscopy at the interband transitions as a semiquantitative tool, enabling the recognition of ABCB domains in tetralayer graphene flakes and, therefore, providing a basis to study correlation physics of this exciting phase.

Metasurfaces with perfect infrared absorption promise integrated filters and compact detector elements with narrowband thermal emission. Phase‐change materials (PCMs) are prime candidates for active, non‐volatile absorption tuning. Commonly, the response of the entire metasurface is tuned, while local adaptions remain elusive. In this work, flexible encoding of different absorption/emission properties within a metasurface is shown. The plasmonic PCM In3SbTe2 (IST) is employed to obtain control over the emissivity by patterning an adaptable grating absorber metasurface. Using a commercial direct laser writing setup, the IST is locally switched from an amorphous dielectric into a crystalline metallic state, and cm‐sized stripe gratings are written above a reflecting mirror. Modification of already written patterns is demonstrated by changing the laser power and thus the IST stripe width to encode different polarization‐sensitive patterns with nearly perfect absorption into the same metasurface. Finally, an apparent local temperature pattern due to the large‐area emissivity shaping metasurface is measured with a conventional thermal camera. The results pave the way towards low‐cost, large‐area, and adaptable patterning of metasurfaces with wavelength and polarization‐selective perfect absorption, enabling applications like enhanced thermal detection, infrared camouflage, or encoding anti‐counterfeiting symbols.

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 SiO2. 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.

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