Far-Field and Near-Field Manipulation via Multipole Coupling Phenomenon in Van der Waals Metasurfaces

The advent of a new era of flat optics is due to the optical metasurfaces, whose large number of degrees of freedom allowed one to fabricate various optical elements on a single technological platform. The use of van der Waals (vdW) layered materials, which have a remarkable combination of a high refractive index, record optical anisotropy and bright exciton resonances, can lead to operating regimes of metasurfaces that are unattainable for their dielectric counterparts. In this work, the degree of freedom related to the optical anisotropy is used for control of the balance and competition of modes of vdW resonators, leading to the observation of both the well-known hybrid anapole effect and recently predicted octupole quasi-trapped mode (OQTM) regime in the same metasurface. Using far-field and near-field analysis of the metasurface composed of ${\mathrm{MoS}}_2$ disks, both the common and significantly different features of these two effects are demonstrated and it is found that the remarkable combination of narrow spectral features and strong energy localization makes OQTM-supported vdW metasurfaces a much more attractive alternative for creating flat nanophotonic devices, including narrowband converters, light concentrators, as well as surface-emitting lasers and nonlinear light converters.