ABSTRACT
Tailoring light-matter interaction is essential to realize nanophotonic components. It can be achieved with surface phonon polaritons (SPhPs), an excitation of photons coupled with phonons of polar crystals, which also occur in 2d materials such as hexagonal boron nitride or anisotropic crystals. Ultra-confined resonances are observed by restricting the SPhPs to cavities. Phase-change materials (PCMs) enable non-volatile programming of these cavities based on a change in the refractive index. Recently, the plasmonic PCM In3SbTe2 (IST) was introduced which can be reversibly switched from an amorphous dielectric state to a crystalline metallic one in the entire infrared to realize numerous nanoantenna geometries. However, reconfiguring SPhP resonators to modify the confined polaritons modes remains elusive. Here, we demonstrate direct programming of confined SPhP resonators by phase-switching IST on top of a polar silicon carbide crystal and investigate the strongly confined resonance modes with scanning near-field optical microscopy. Reconfiguring the size of the resonators themselves result in enhanced mode confinements up to a value of λ / 35 . Finally, unconventional cavity shapes with complex field patterns are explored as well. This study is a first step towards rapid prototyping of reconfigurable SPhP resonators that can be easily transferred to hyperbolic and anisotropic 2d materials.
ABSTRACT
Phase-change materials (PCMs) have been established as prime candidates for nonvolatile resonance tuning of nanophotonic components based on a large optical contrast between their amorphous and crystalline states. Recently, the plasmonic PCM In3SbTe2 was introduced, which can be switched from an amorphous dielectric state to a crystalline metallic one over the entire infrared spectral range. While locally switching the PCM around metallic nanorod antennas has already been demonstrated, similar tuning of inverse antenna structures (nanoslits) has not yet been investigated. Here, we demonstrate optical resonance tuning of nanoslit antennas with dielectric and plasmonic PCMs. We compare two geometries with fundamentally different resonance tuning mechanisms: tuning the resonance of aluminum slit antennas by change of the refractive index (dielectric PCM Ge3Sb2Te6), and creating slit-like volumes of amorphous In3SbTe2 and modifying the slit geometry directly (plasmonic PCM In3SbTe2). While the tuning range with the plasmonic PCM is about 3.4 µm and only limited by fabrication, the resonances with the dielectric PCM feature a three times larger quality factor compared to resonances obtained with the plasmonic PCM.
ABSTRACT
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.
